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• What is a good way to simulate O_NOFOLLOW on systems without this flag?

  - by Daniel Trebbien

  I would like to safely be able to simulate open with O_CREAT | O_WRONLY | O_TRUNC | O_NOFOLLOW and O_CREAT | O_WRONLY | O_APPEND | O_NOFOLLOW on systems that do not support O_NOFOLLOW. I can somewhat achieve what I am asking for with: struct stat lst; if (lstat(filename, &lst) != -1 && S_ISLNK(lst.st_mode)) { errno = ELOOP; return -1; } mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; int fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC | O_NOFOLLOW, mode); but then I introduce a race condition and possibly a security problem. I thought about maybe creating a dummy file with only the user being able to write, kind of like touching filename, doing the lstat check, and then using chmod after I finish writing (to correct the file mode bits), but I could be overlooking something major (e.g. if the file at filename exists, is not a regular file, or is already a symbolic link). What do you think?

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• SOA Suite 11g Native Format Builder Complex Format Example

  - by bob.webster

  This rather long posting details the steps required to process a grouping of fixed length records using Format Builder.   If it’s 10 pm and you’re feeling beat you might want to leave this until tomorrow.  But if it’s 10 pm and you need to get a Format Builder Complex template done, read on… The goal is to process individual orders from a file using the 11g File Adapter and Format Builder Sample Data =========== 001Square Widget            0245.98 102Triagular Widget         1120.00 403Circular Widget           0099.45 ORD8898302/01/2011 301Hexagon Widget         1150.98 ORD6735502/01/2011 The records are fixed length records representing a number of logical Order records. Each order record consists of a number of item records starting with a 3 digit number, followed by a single Summary Record which starts with the constant ORD. How can this file be processed so that the first poll returns the first order? 001Square Widget            0245.98 102Triagular Widget         1120.00 403Circular Widget           0099.45 ORD8898302/01/2011 And the second poll returns the second order? 301Hexagon Widget           1150.98 ORD6735502/01/2011 Note: if you need more than one order per poll, that’s also possible, see the “Multiple Messages” field in the “File Adapter Step 6 of 9” snapshot further down.   To follow along with this example you will need - Studio Edition Version 11.1.1.4.0    with the   - SOA Extension for JDeveloper 11.1.1.4.0 installed Both can be downloaded from here:  http://www.oracle.com/technetwork/middleware/soasuite/downloads/index.html You will not need a running WebLogic Server domain to complete the steps and Format Builder tests in this article.     Start with a SOA Composite containing a File Adapter The Format Builder is part of the File Adapter so start by creating a new SOA Project and Composite. Here is a quick summary for those not familiar with these steps - Start JDeveloper - From the Main Menu choose File->New - In the New Gallery window that opens Expand the “General” category and Select the Applications node.   Then choose SOA Application from the Items section on the right.  Finally press the OK button. - In Step 1 of the “Create SOA Application wizard” that appears enter an Application Name and an Directory of your     choice,   then press the Next button. - In Step 2 of the “Create SOA Application wizard”, press the Next button leaving all entries as defaulted. - In Step 3 of the “Create SOA Application wizard”, Enter a composite name of your choice and Press the Finish   Button These steps result in a new Application and SOA Project. The SOA Project contains a composite.xml file which is opened and shown below. For our example we have not defined a Mediator or a BPEL process to minimize the steps, but one or the other would eventually be needed to use the File Adapter we are about to create. Drag and drop the File Adapter icon from the Component Pallette onto either the LEFT side of the diagram under “Exposed Services” or the right side under “External References”.  (See the Green Circle in the image below).  Placing the adapter on the left side would indicate the file being processed is inbound to the composite, if the adapter is placed on the right side then the data is outbound to a file.     Note that the same Format Builder definition can be used in both directions.  For example we could use the format with a File Adapter on the left side of the composite to parse fixed data into XML, modify the data in our Composite or BPEL process and then use the same Format Builder definition with a File adapter on the right side of the composite to write the data back out in the same fixed data format When the File Adapter is dropped on the Composite the File Adapter Wizard Appears. Skip Past the first page, Step 1 of 9 by pressing the Next button. In Step 2 enter a service name of your choice as shown below, then press Next   When the Native Format Builder appears, skip the welcome page by pressing next. Also press the Next button to accept the settings on Step 3 of 9 On Step 4, select Read File and press the Next button as shown below.   On Step 5 enter a directory that will contain a file with the input data, then  Press the Next button as shown below. In step 6, enter *.txt or another file format to select input files from the input directory mentioned in step 5. ALSO check the “Files contain Multiple Messages” checkbox and set the “Publish Messages in Batches of” field to 1.  The value can be set higher to increase the number of logical order group records returned on each poll of the file adapter.  In other words, it determines the number of Orders that will be sent to each instance of a Mediator or Composite processing using the File Adapter.   Skip Step 7 by pressing the Next button In Step 8 press the Gear Icon on the right side to load the Native Format Builder.       Native Format Builder  appears Before diving into the format, here is an overview of the process. Approach - Bottom up Assuming an Order is a grouping of item records and a summary record…. - Define a separate  Complex Type for each Record Type found in the group.    (One for itemRecord and one for summaryRecord) - Define a Complex Type to contain the Group of Record types defined above   (LogicalOrderRecord) - Define a top level element to represent an order.  (order)   The order element will be of type LogicalOrderRecord   Defining the Format In Step 1 select   “Create new”  and  “Complex Type” and “Next”   In Step two browse to and select a file containing the test data shown at the start of this article. A link is provided at the end of this article to download a file containing the test data. Press the Next button     In Step 3 Complex types must be define for each type of input record. Select the Root-Element and Click on the Add Complex Type icon This creates a new empty complex type definition shown below. The fastest way to create the definition is to highlight the first line of the Sample File data and drag the line onto the  <new_complex_type> Format Builder introspects the data and provides a grid to define additional fields. Change the “Complex Type Name” to  “itemRecord” Then click on the ruler to indicate the position of fixed columns.  Drag the red triangle icons to the exact columns if necessary. Double click on an existing red triangle to remove an unwanted entry. In the case below fields are define in columns 0-3, 4-28, 29-eol When the field definitions are correct, press the “Generate Fields” button. Field entries named C1, C2 and C3 will be created as shown below. Click on the field names and rename them from C1->itemNum, C2->itemDesc and C3->itemCost  When all the fields are correctly defined press OK to save the complex type.        Next, the process is repeated to define a Complex Type for the SummaryRecord. Select the Root-Element in the schema tree and press the new complex type icon Then highlight and drag the Summary Record from the sample data onto the <new_complex_type>   Change the complex type name to “summaryRecord” Mark the fixed fields for Order Number and Order Date. Press the Generate Fields button and rename C1 and C2 to itemNum and orderDate respectively.   The last complex type to be defined is a type to hold the group of items and the summary record. Select the Root-Element in the schema tree and click the new complex type icon Select the “<new_complex_type>” entry and click the pencil icon   On the Complex Type Details page change the name and type of each input field. Change line 1 to be named item and set the Type  to “itemRecord” Change line 2 to be named summary and set the Type to “summaryRecord” We also need to indicate that itemRecords repeat in the input file. Click the pencil icon at the right side of the item line. On the Edit Details page change the “Max Occurs” entry from 1 to UNBOUNDED. We also need to indicate how to identify an itemRecord.  Since each item record has “.” in column 32 we can use this fact to differentiate an item record from a summary record. Change the “Look Ahead” field to value 32 and enter a period in the “Look For” field Press the OK button to save entry.     Finally, its time to create a top level element to represent an order. Select the “Root-Element” in the schema tree and press the New element icon Click on the <new_element> and press the pencil icon.   Set the Element Name to “order” and change the Data Type to “logicalOrderRecord” Press the OK button to save the element definition.   The final definition should match the screenshot below. Press the Next Button to view the definition source.     Press the Test Button to test the definition   Press the Green Triangle Icon to run the test.   And we are presented with an unwelcome error. The error states that the processor ran out of data while working through the definition. The processor was unable to differentiate between itemRecords and summaryRecords and therefore treated the entire file as a list of itemRecords.  At end of file, the “summary” portion of the logicalOrderRecord remained unprocessed but mandatory.   This root cause of this error is the loss of our “lookAhead” definition used to identify itemRecords. This appears to be a bug in the  Native Format Builder 11.1.1.4.0 Luckily, a simple workaround exists. Press the Cancel button and return to the “Step 4 of 4” Window. Manually add    nxsd:lookAhead="32" nxsd:lookFor="."   attributes after the maxOccurs attribute of the item element. as shown in the highlighted text below.   When the lookAhead and lookFor attributes have been added Press the Test button and on the Test page press the Green Triangle. The test is now successful, the first order in the file is returned by the File Adapter.     Below is a complete listing of the Result XML from the right column of the screen above   Try running it The downloaded input test file and completed schema file can be used for testing without following all the Native Format Builder steps in this example. Use the following link to download a file containing the sample data. Download Sample Input Data This is the best approach rather than cutting and pasting the input data at the top of the article.  Since the data is fixed length it’s very important to watch out for trailing spaces in the data and to ensure an eol character at the end of every line. The download file is correctly formatted. The final schema definition can be downloaded at the following link Download Completed Schema Definition   - Save the inputData.txt file to a known location like the xsd folder in your project. - Save the inputData_6.xsd file to the xsd folder in your project. - At step 1 in the Native Format Builder wizard  (as shown above) check the “Edit existing” radio button,    then browse and select the inputData_6.xsd file - At step 2 of the Format Builder configuration Wizard (as shown above) supply the path and filename for    the inputData.txt file. - You can then proceed to the test page and run a test. - Remember the wizard bug will drop the lookAhead and lookFor attributes,  you will need to manually add   nxsd:lookAhead="32" nxsd:lookFor="."    after the maxOccurs attribute of the item element in the   LogicalOrderRecord Complex Type.  (as shown above)   Good Luck with your Format Project

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• SSH problems (ssh_exchange_identification: read: Connection reset by peer)

  - by kSiR

  I was running 11.10 and decided to do the full upgrade and come up to 12.04 after the update SSH (not SSHD) is now misbehaving when attempting to connect to other OpenSSH instances. I say OpenSSH as I am running a DropBear sshd on my router and I am able to connect to it. When attempting to connect to an OpenSSH server risk@skynet:~/.ssh$ ssh -vvv risk@someserver OpenSSH_5.9p1 Debian-5ubuntu1, OpenSSL 1.0.1 14 Mar 2012 debug1: Reading configuration data /home/risk/.ssh/config debug3: key names ok: [[email protected],[email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,ssh-dss] debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: Applying options for * debug2: ssh_connect: needpriv 0 debug1: Connecting to someserver [someserver] port 22. debug1: Connection established. debug1: identity file /home/risk/.ssh/id_rsa type -1 debug1: identity file /home/risk/.ssh/id_rsa-cert type -1 debug1: identity file /home/risk/.ssh/id_dsa type -1 debug1: identity file /home/risk/.ssh/id_dsa-cert type -1 debug3: Incorrect RSA1 identifier debug3: Could not load "/home/risk/.ssh/id_ecdsa" as a RSA1 public key debug1: identity file /home/risk/.ssh/id_ecdsa type 3 debug1: Checking blacklist file /usr/share/ssh/blacklist.ECDSA-521 debug1: Checking blacklist file /etc/ssh/blacklist.ECDSA-521 debug1: identity file /home/risk/.ssh/id_ecdsa-cert type -1 ssh_exchange_identification: read: Connection reset by peer risk@skynet:~/.ssh$ DropBear instance risk@skynet:~/.ssh$ ssh -vvv root@darkness OpenSSH_5.9p1 Debian-5ubuntu1, OpenSSL 1.0.1 14 Mar 2012 debug1: Reading configuration data /home/risk/.ssh/config debug3: key names ok: [[email protected],[email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,ssh-dss] debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: Applying options for * debug2: ssh_connect: needpriv 0 debug1: Connecting to darkness [192.168.1.1] port 22. debug1: Connection established. debug1: identity file /home/risk/.ssh/id_rsa type -1 debug1: identity file /home/risk/.ssh/id_rsa-cert type -1 debug1: identity file /home/risk/.ssh/id_dsa type -1 debug1: identity file /home/risk/.ssh/id_dsa-cert type -1 debug3: Incorrect RSA1 identifier debug3: Could not load "/home/risk/.ssh/id_ecdsa" as a RSA1 public key debug1: identity file /home/risk/.ssh/id_ecdsa type 3 debug1: Checking blacklist file /usr/share/ssh/blacklist.ECDSA-521 debug1: Checking blacklist file /etc/ssh/blacklist.ECDSA-521 debug1: identity file /home/risk/.ssh/id_ecdsa-cert type -1 debug1: Remote protocol version 2.0, remote software version dropbear_0.52 debug1: no match: dropbear_0.52 ... I have googled and ran most ALL fixes recommend both from the Debian and Arch sides and none of them seem to resolve my issue. Any ideas?

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• Configuring Novel iPrint client on ubuntu 13.10

  - by Mahdi Sadeghi

  Recently I have struggled a lot to make Novel iPrint client to work on my laptop. I need it to use Follow Me printers in our university(you can take your print form any printer). Using this tutorial from Novel, I tried to convert the rpm package and install it on Ubuntu 13.04 & 13.10. The post install script from installing generated deb package had a typo which I saw in post install messages and I fixed that. Now I have the client running. To see the client UI I installed cinnamon desktop(because unity does not have system tray and old solutions did'nt work to whitelist Novel clinet). I have iPrint plugin installed on firefox as well(I copied the shared object files to plugin directories). I try installing printers from provided ipp URL(which lists available printers on the server) with no success. After clicking the printer name I see this: I have various errors: Formerly firefox used to asked my network username/password for installing SSL printer but now it returns this: iPrint Printer - The printer is currently not available. However I can install non-SSL version but the printer location is either empty or points to: file:///dev/null even if I change it to the exact address which I see on working machines still it prints nothing. I have tried the novel command line tool, iprntcmd to print. It is being installed at: /opt/novell/iprint/bin/ msadeghi@werkstatt:/opt/novell/iprint/bin$ ./iprntcmd --addprinter ipp://iprint.rz.hs-offenburg.de/ipp/Follow-me\ -\ IPP iprntcmd v05.04.00 Adding printer ipp://iprint.rz.hs-offenburg.de/ipp/Follow-me - IPP. Added printer ipp://iprint.rz.hs-offenburg.de/ipp/Follow-me - IPP successfully. It adds the printer with empty location and again no print. What I found interesting is the log file at ~/.iprint/errors.txt with strange errors which I hope somebody here can understand. When I try to install the SSL printer I receive these logs(note that HP is my local printer and has nothing to do with iprint): Thu Oct 31 11:02:03 2013 Trace Info: iprint.c, line 6690 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for file:///dev/null - Unknown Port Type - file Thu Oct 31 11:02:03 2013 Trace Info: iprint.c, line 6800 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for hp:/usb/HP_LaserJet_1018?serial=KP103A1 - No Port type specified Thu Oct 31 11:02:05 2013 Trace Info: iprint.c, line 6690 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for file:///dev/null - Unknown Port Type - file Thu Oct 31 11:02:05 2013 Trace Info: iprint.c, line 6800 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for hp:/usb/HP_LaserJet_1018?serial=KP103A1 - No Port type specified Thu Oct 31 11:02:06 2013 Trace Info: mydoreq.c, line 676 Group Info: CLIB Error Code: 0 (0x0) User ID: 1000 Error Msg: Success Debug Msg: MyCupsDoFileRequest - httpReconnect failed (0) Thu Oct 31 11:02:06 2013 Trace Info: mydoreq.c, line 1293 Group Info: CUPS-IPP Error Code: 1282 (0x502) User ID: 1000 Error Msg: iPrint Printer - The printer is currently not available. Debug Msg: MyCupsDoFileRequest - IPP SERVICE UNAVAILABLE Thu Oct 31 11:02:06 2013 Trace Info: iprint.c, line 6690 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for file:///dev/null - Unknown Port Type - file Thu Oct 31 11:02:06 2013 Trace Info: iprint.c, line 6800 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for hp:/usb/HP_LaserJet_1018?serial=KP103A1 - No Port type specified Thu Oct 31 11:02:08 2013 Trace Info: iprint.c, line 6690 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for file:///dev/null - Unknown Port Type - file Thu Oct 31 11:02:08 2013 Trace Info: iprint.c, line 6800 Group Info: IPRINT-lib Error Code: 4096 (0x1000) User ID: 1000 Error Msg: iPrint Lib - Bad URI type supplied (not IPP:, HTTP:, or HTTPS:). Debug Msg: IPRINTInterpretURI for hp:/usb/HP_LaserJet_1018?serial=KP103A1 - No Port type specified I should say that my friend can print using the same instructions on CrunchBang easily and another guy on 12.04 LTS but with more struggling. It worked for me on linux mint maya with my old laptop as well. Is there anybody out there who can help me to solve these problems? I am really disappointed with Novell and our university support. PS. I had the same problemwith 13.04. No matter if I am within the network or I connect with VPN, I have the same issues.

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• Cloud MBaaS : The Next Big Thing in Enterprise Mobility

  - by shiju

  In this blog post, I will take a look at Cloud Mobile Backend as a Service (MBaaS) and how we can leverage Cloud based Mobile Backend as a Service for building enterprise mobile apps. Today, mobile apps are incredibly significant in both consumer and enterprise space and the demand for the mobile apps is unbelievably increasing in day to day business. An enterprise can’t survive in business without a proper mobility strategy. A better mobility strategy and faster delivery of your mobile apps will give you an extra mileage for your business and IT strategy. So organizations and mobile developers are looking for different strategy for meeting this demand and adopting different development strategy for their mobile apps. Some developers are adopting hybrid mobile app development platforms, for delivering their products for multiple platforms, for fast time-to-market. Others are adopting a Mobile enterprise application platform (MEAP) such as Kony for their enterprise mobile apps for fast time-to-market and better business integration. The Challenges of Enterprise Mobility The real challenge of enterprise mobile apps, is not about creating the front-end environment or developing front-end for multiple platforms. The most important thing of enterprise mobile apps is to expose your enterprise data to mobile devices where the real pain is your business data might be residing in lot of different systems including legacy systems, ERP systems etc., and these systems will be deployed with lot of security restrictions. Exposing your data from the on-premises servers, is not a easy thing for most of the business organizations. Many organizations are spending too much time for their front-end development strategy, but they are really lacking for building a strategy on their back-end for exposing the business data to mobile apps. So building a REST services layer and mobile back-end services, on the top of legacy systems and existing middleware systems, is the key part of most of the enterprise mobile apps, where multiple mobile platforms can easily consume these REST services and other mobile back-end services for building mobile apps. For some mobile apps, we can’t predict its user base, especially for products where customers can gradually increase at any time. And for today’s mobile apps, faster time-to-market is very critical so that spending too much time for mobile app’s scalability, will not be worth. The real power of Cloud is the agility and on-demand scalability, where we can scale-up and scale-down our applications very easily. It would be great if we could use the power of Cloud to mobile apps. So using Cloud for mobile apps is a natural fit, where we can use Cloud as the storage for mobile apps and hosting mechanism for mobile back-end services, where we can enjoy the full power of Cloud with greater level of on-demand scalability and operational agility. So Cloud based Mobile Backend as a Service is great choice for building enterprise mobile apps, where enterprises can enjoy the massive scalability power of their mobile apps, provided by public cloud vendors such as Microsoft Windows Azure. Mobile Backend as a Service (MBaaS) We have discussed the key challenges of enterprise mobile apps and how we can leverage Cloud for hosting mobile backend services. MBaaS is a set of cloud-based, server-side mobile services for multiple mobile platforms and HTML5 platform, which can be used as a backend for your mobile apps with the scalability power of Cloud. The information below provides the key features of a typical MBaaS platform: Cloud based storage for your application data. Automatic REST API services on the application data, for CRUD operations. Native push notification services with massive scalability power. User management services for authenticate users. User authentication via Social accounts such as Facebook, Google, Microsoft, and Twitter. Scheduler services for periodically sending data to mobile devices. Native SDKs for multiple mobile platforms such as Windows Phone and Windows Store, Android, Apple iOS, and HTML5, for easily accessing the mobile services from mobile apps, with better security.  Typically, a MBaaS platform will provide native SDKs for multiple mobile platforms so that we can easily consume the server-side mobile services. MBaaS based REST APIs can use for integrating to enterprise backend systems. We can use the same mobile services for multiple platform so hat we can reuse the application logic to multiple mobile platforms. Public cloud vendors are building the mobile services on the top of their PaaS offerings. Windows Azure Mobile Services is a great platform for a MBaaS offering that is leveraging Windows Azure Cloud platform’s PaaS capabilities. Hybrid mobile development platform Titanium provides their own MBaaS services. LoopBack is a new MBaaS service provided by Node.js consulting firm StrongLoop, which can be hosted on multiple cloud platforms and also for on-premises servers. The Challenges of MBaaS Solutions If you are building your mobile apps with a new data storage, it will be very easy, since there is not any integration challenges you have to face. But most of the use cases, you have to extract your application data in which stored in on-premises servers which might be under VPNs and firewalls. So exposing these data to your MBaaS solution with a proper security would be a big challenge. The capability of your MBaaS vendor is very important as you have to interact with your legacy systems for many enterprise mobile apps. So you should be very careful about choosing for MBaaS vendor. At the same time, you should have a proper strategy for mobilizing your application data which stored in on-premises legacy systems, where your solution architecture and strategy is more important than platforms and tools.  Windows Azure Mobile Services Windows Azure Mobile Services is an MBaaS offerings from Windows Azure cloud platform. IMHO, Microsoft Windows Azure is the best PaaS platform in the Cloud space. Windows Azure Mobile Services extends the PaaS capabilities of Windows Azure, to mobile devices, which can be used as a cloud backend for your mobile apps, which will provide global availability and reach for your mobile apps. Windows Azure Mobile Services provides storage services, user management with social network integration, push notification services and scheduler services and provides native SDKs for all major mobile platforms and HTML5. In Windows Azure Mobile Services, you can write server-side scripts in Node.js where you can enjoy the full power of Node.js including the use of NPM modules for your server-side scripts. In the previous section, we had discussed some challenges of MBaaS solutions. You can leverage Windows Azure Cloud platform for solving many challenges regarding with enterprise mobility. The entire Windows Azure platform can play a key role for working as the backend for your mobile apps where you can leverage the entire Windows Azure platform for your mobile apps. With Windows Azure, you can easily connect to your on-premises systems which is a key thing for mobile backend solutions. Another key point is that Windows Azure provides better integration with services like Active Directory, which makes Windows Azure as the de facto platform for enterprise mobility, for enterprises, who have been leveraging Microsoft ecosystem for their application and IT infrastructure. Windows Azure Mobile Services  is going to next evolution where you can expect some exciting features in near future. One area, where Windows Azure Mobile Services should definitely need an improvement, is about the default storage mechanism in which currently it is depends on SQL Server. IMHO, developers should be able to choose multiple default storage option when creating a new mobile service instance. Let’s say, there should be a different storage providers such as SQL Server storage provider and Table storage provider where developers should be able to choose their choice of storage provider when creating a new mobile services project. I have been used Windows Azure and Windows Azure Mobile Services as the backend for production apps for mobile, where it performed very well. MBaaS Over MEAP Recently, many larger enterprises has been adopted Mobile enterprise application platform (MEAP) for their mobile apps. I haven’t worked on any production MEAP solution, but I heard that developers are really struggling with MEAP in different way. The learning curve for a proprietary MEAP platform is very high. I am completely against for using larger proprietary ecosystem for mobile apps. For enterprise mobile apps, I highly recommend to use native iOS/Android/Windows Phone or HTML5  for front-end with a cloud hosted MBaaS solution as the middleware. A MBaaS service can be consumed from multiple mobile apps where REST APIs are using to integrating with enterprise backend systems. Enterprise mobility should start with exposing REST APIs on the enterprise backend systems and these REST APIs can host on Cloud where we can enjoy the power of Cloud for our services. If you are having REST APIs for your enterprise data, then you can easily build mobile frontends for multiple platforms.   You can follow me on Twitter @shijucv

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• Know more about Enqueue Deadlock Detection

  - by Liu Maclean(???)

  ??? ORACLE ALLSTAR???????????????????,??????? ???????enqueue lock?????????3 ??????,????????????????????????????ora-00060 dead lock??process???3s: SQL> select * from v$version; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi PL/SQL Release 10.2.0.5.0 - Production CORE 10.2.0.5.0 Production TNS for Linux: Version 10.2.0.5.0 - Production NLSRTL Version 10.2.0.5.0 - Production SQL> select * from global_name; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com PROCESS A: set timing on; update maclean1 set t1=t1+1; PROCESS B: update maclean2 set t1=t1+1; PROCESS A: update maclean2 set t1=t1+1; PROCESS B: update maclean1 set t1=t1+1; ??3s? PROCESS A ?? ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:03.02 ????Process A????????????? 3s,?????????????,??????? ?????????? ???????: SQL> col name for a30 SQL> col value for a5 SQL> col DESCRIB for a50 SQL> set linesize 140 pagesize 1400 SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y 3 WHERE x.inst_id = USERENV ('Instance') 4 AND y.inst_id = USERENV ('Instance') 5 AND x.indx = y.indx 6 AND x.ksppinm='_enqueue_deadlock_scan_secs'; NAME VALUE DESCRIB ------------------------------ ----- -------------------------------------------------- _enqueue_deadlock_scan_secs 0 deadlock scan interval SQL> alter system set "_enqueue_deadlock_scan_secs"=18 scope=spfile; System altered. Elapsed: 00:00:00.01 SQL> startup force; ORACLE instance started. Total System Global Area 851443712 bytes Fixed Size 2100040 bytes Variable Size 738198712 bytes Database Buffers 104857600 bytes Redo Buffers 6287360 bytes Database mounted. Database opened. PROCESS A: SQL> set timing on; SQL> update maclean1 set t1=t1+1; 1 row updated. Elapsed: 00:00:00.06 Process B SQL> update maclean2 set t1=t1+1; 1 row updated. SQL> update maclean1 set t1=t1+1; Process A: SQL> SQL> alter session set events '10704 trace name context forever,level 10:10046 trace name context forever,level 8'; Session altered. SQL> update maclean2 set t1=t1+1; update maclean2 set t1=t1+1 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource  Elapsed: 00:00:18.05 ksqcmi: TX,90011,4a9 mode=6 timeout=21474836 WAIT #12: nam='enq: TX - row lock contention' ela= 2930070 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114759849120 WAIT #12: nam='enq: TX - row lock contention' ela= 2930636 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114762779801 WAIT #12: nam='enq: TX - row lock contention' ela= 2930439 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114765710430 *** 2012-06-12 09:58:43.089 WAIT #12: nam='enq: TX - row lock contention' ela= 2931698 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114768642192 WAIT #12: nam='enq: TX - row lock contention' ela= 2930428 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114771572755 WAIT #12: nam='enq: TX - row lock contention' ela= 2931408 name|mode=1415053318 usn<<16 | slot=589841 sequence=1193 obj#=56810 tim=1308114774504207 DEADLOCK DETECTED ( ORA-00060 ) [Transaction Deadlock] The following deadlock is not an ORACLE error. It is a deadlock due to user error in the design of an application or from issuing incorrect ad-hoc SQL. The following information may aid in determining the deadlock: ??????Process A?’enq: TX – row lock contention’ ?????ORA-00060 deadlock detected????3s ??? 18s , ???hidden parameter “_enqueue_deadlock_scan_secs”?????,????????0? ??????????: SQL> alter system set "_enqueue_deadlock_scan_secs"=4 scope=spfile; System altered. Elapsed: 00:00:00.01 SQL> alter system set "_enqueue_deadlock_time_sec"=9 scope=spfile; System altered. Elapsed: 00:00:00.00 SQL> startup force; ORACLE instance started. Total System Global Area 851443712 bytes Fixed Size 2100040 bytes Variable Size 738198712 bytes Database Buffers 104857600 bytes Redo Buffers 6287360 bytes Database mounted. Database opened. SQL> set linesize 140 pagesize 1400 SQL> show parameter dead NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _enqueue_deadlock_scan_secs integer 4 _enqueue_deadlock_time_sec integer 9 SQL> set timing on SQL> select * from maclean1 for update wait 8; T1 ---------- 11 Elapsed: 00:00:00.01 PROCESS B SQL> select * from maclean2 for update wait 8; T1 ---------- 3 SQL> select * from maclean1 for update wait 8; select * from maclean1 for update wait 8 PROCESS A SQL> select * from maclean2 for update wait 8; select * from maclean2 for update wait 8 * ERROR at line 1: ORA-30006: resource busy; acquire with WAIT timeout expired Elapsed: 00:00:08.00 ???????? ??? select for update wait?enqueue request timeout ?????8s? ,???????”_enqueue_deadlock_scan_secs”=4(deadlock scan interval),?4s???deadlock detected,????Process A????deadlock ???, ??????? ??Process A?????8s?raised??”ORA-30006: resource busy; acquire with WAIT timeout expired”??,??ORA-00060,?????process A???????? ????????”_enqueue_deadlock_time_sec”(requests with timeout <= this will not have deadlock detection)???,?enqueue request time < “_enqueue_deadlock_time_sec”?Server process?????dead lock detection,?????????enqueue request ??????timeout??????(_enqueue_deadlock_time_sec????5,?timeout<5s),???????????????;??????timeout>”_enqueue_deadlock_time_sec”???,Oracle????????????????????? ??????????: SQL> show parameter dead NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _enqueue_deadlock_scan_secs integer 4 _enqueue_deadlock_time_sec integer 9 Process A: SQL> set timing on; SQL> select * from maclean1 for update wait 10; T1 ---------- 11 Process B: SQL> select * from maclean2 for update wait 10; T1 ---------- 3 SQL> select * from maclean1 for update wait 10; PROCESS A: SQL> select * from maclean2 for update wait 10; select * from maclean2 for update wait 10 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:06.02 ??????? select for update wait 10?10s??, ?? 10s?????_enqueue_deadlock_time_sec???(9s),??Process A???????? ???????????????6s ???????_enqueue_deadlock_scan_secs?4s ? ???????????,???????????_enqueue_deadlock_scan_secs?????????3???? ??: enqueue lock?????????????? 1. ?????????deadlock detection??3s????, ????????_enqueue_deadlock_scan_secs(deadlock scan interval)???,??????0,????????_enqueue_deadlock_scan_secs?????????3???, ?_enqueue_deadlock_scan_secs=0 ??3s??, ?_enqueue_deadlock_scan_secs=4??6s??,????? 2. ???????_enqueue_deadlock_time_sec(requests with timeout <= this will not have deadlock detection)???,?enqueue request timeout< _enqueue_deadlock_time_sec(????5),?Server process?????????enqueue request timeout>_enqueue_deadlock_time_sec ????_enqueue_deadlock_scan_secs???????, ??request timeout??????select for update wait [TIMEOUT]??? ??: ???10.2.0.1?????????2?hidden parameter , ???patchset 10.2.0.3????? _enqueue_deadlock_time_sec, ?patchset 10.2.0.5??????_enqueue_deadlock_scan_secs? ?????RAC???????????10s, ???????_lm_dd_interval(dd time interval in seconds) ,????????8.0.6???? ???????????????,??????,  ?10g???????60s,?11g???????10s?  ???????11g??_lm_dd_interval?????????????,?????11g??LMD????????????,??????????RAC?LMD?Deadlock Detection???????CPU,???11g?Oracle????Team???LMD????????CPU????: ????????11g?LMD???????,???????11g??? UTS TRACE ????? DD???: SQL> select * from v$version; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production PL/SQL Release 11.2.0.3.0 - Production CORE 11.2.0.3.0 Production TNS for Linux: Version 11.2.0.3.0 - Production NLSRTL Version 11.2.0.3.0 - Production SQL> SQL> select * from global_name 2 ; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com SQL> alter system set "_lm_dd_interval"=20 scope=spfile; System altered. SQL> startup force; ORACLE instance started. Total System Global Area 1570009088 bytes Fixed Size 2228704 bytes Variable Size 1325403680 bytes Database Buffers 234881024 bytes Redo Buffers 7495680 bytes Database mounted. Database opened. SQL> set linesize 140 pagesize 1400 SQL> show parameter lm_dd NAME TYPE VALUE ------------------------------------ -------------------------------- ------------------------------ _lm_dd_interval integer 20 SQL> select count(*) from gv$instance; COUNT(*) ---------- 2 instance 1: SQL> oradebug setorapid 12 Oracle pid: 12, Unix process pid: 8608, image: [email protected] (LMD0) ? LMD0??? UTS TRACE??RAC???????????? SQL> oradebug event 10046 trace name context forever,level 8:10708 trace name context forever,level 103: trace[rac.*] disk high; Statement processed. Elapsed: 00:00:00.00 SQL> update maclean1 set t1=t1+1; 1 row updated. instance 2: SQL> update maclean2 set t1=t1+1; 1 row updated. SQL> update maclean1 set t1=t1+1; Instance 1: SQL> update maclean2 set t1=t1+1; update maclean2 set t1=t1+1 * ERROR at line 1: ORA-00060: deadlock detected while waiting for resource Elapsed: 00:00:20.51 LMD0???UTS TRACE 2012-06-12 22:27:00.929284 : [kjmpbmsg:process][type 22][msg 0x7fa620ac85a8][from 1][seq 8148.0][len 192] 2012-06-12 22:27:00.929346 : [kjmxmpm][type 22][seq 0.0][msg 0x7fa620ac85a8][from 1] *** 2012-06-12 22:27:00.929 * kjddind: received DDIND msg with subtype x6 * reqp->dd_master_inst_kjxmddi == 1 * kjddind: dump sgh: 2012-06-12 22:27:00.929346*: kjddind: req->timestamp [0.15], kjddt [0.13] 2012-06-12 22:27:00.929346*: >> DDmsg:KJX_DD_REMOTE,TS[0.15],Inst 1->2,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.929346*: lock [0x95023930,829], op = [mast] 2012-06-12 22:27:00.929346*: reqp->timestamp [0.15], kjddt [0.13] 2012-06-12 22:27:00.929346*: kjddind: updated local timestamp [0.15] * kjddind: case KJX_DD_REMOTE 2012-06-12 22:27:00.929346*: ADD IO NODE WFG: 0 frame pointer 2012-06-12 22:27:00.929346*: PUSH: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: POP: type=res, enqueue(0xffffffff.0xffffffff)=0xbbb9af40, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: kjddopr[TX 0xe000c.0x32][ext 0x5,0x0]: blocking lock 0xbbb9a800, owner 2097154 of inst 2 2012-06-12 22:27:00.929346*: PUSH: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: ADD NODE TO WFG: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: POP: type=txn, enqueue(0xffffffff.0xffffffff)=0xbbb9a800, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: kjddopt: converting lock 0xbbce92f8 on 'TX' 0x80016.0x5d4,txid [2097154,34]of inst 2 2012-06-12 22:27:00.929346*: PUSH: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: PROCESS: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929346*: ADD NODE TO WFG: type=res, enqueue(0xffffffff.0xffffffff)=0xbbce92f8, block=KJUSEREX, snode=1 2012-06-12 22:27:00.929855 : GSIPC:AMBUF: rcv buff 0x7fa620aa8cd8, pool rcvbuf, rqlen 1102 2012-06-12 22:27:00.929878 : GSIPC:GPBMSG: new bmsg 0x7fa620aa8d48 mb 0x7fa620aa8cd8 msg 0x7fa620aa8d68 mlen 192 dest x100 flushsz -1 2012-06-12 22:27:00.929878*: << DDmsg:KJX_DD_REMOTE,TS[0.15],Inst 2->1,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.929878*: lock [0xbbce92f8,287], op = [mast] 2012-06-12 22:27:00.929878*: ADD IO NODE WFG: 0 frame pointer 2012-06-12 22:27:00.929923 : [kjmpbmsg:compl][msg 0x7fa620ac8588][typ p][nmsgs 1][qtime 0][ptime 0] 2012-06-12 22:27:00.929947 : GSIPC:PBAT: flush start. flag 0x79 end 0 inc 4.4 2012-06-12 22:27:00.929963 : GSIPC:PBAT: send bmsg 0x7fa620aa8d48 blen 224 dest 1.0 2012-06-12 22:27:00.929979 : GSIPC:SNDQ: enq msg 0x7fa620aa8d48, type 65521 seq 8325, inst 1, receiver 0, queued 1 012-06-12 22:27:00.929979 : GSIPC:SNDQ: enq msg 0x7fa620aa8d48, type 65521 seq 8325, inst 1, receiver 0, queued 1 2012-06-12 22:27:00.929996 : GSIPC:BSEND: flushing sndq 0xb491dd28, id 0, dcx 0xbc517770, inst 1, rcvr 0 qlen 0 1 2012-06-12 22:27:00.930014 : GSIPC:BSEND: no batch1 msg 0x7fa620aa8d48 type 65521 len 224 dest (1:0) 2012-06-12 22:27:00.930088 : kjbsentscn[0x0.3f72dc][to 1] 2012-06-12 22:27:00.930144 : GSIPC:SENDM: send msg 0x7fa620aa8d48 dest x10000 seq 8325 type 65521 tkts x1 mlen xe00110 2012-06-12 22:27:00.930531 : GSIPC:KSXPCB: msg 0x7fa620aa8d48 status 30, type 65521, dest 1, rcvr 0 WAIT #0: nam='ges remote message' ela= 1372 waittime=80 loop=0 p3=74 obj#=-1 tim=1339554420931640 2012-06-12 22:27:00.931728 : GSIPC:RCVD: ksxp msg 0x7fa620af6490 sndr 1 seq 0.8149 type 65521 tkts 1 2012-06-12 22:27:00.931746 : GSIPC:RCVD: watq msg 0x7fa620af6490 sndr 1, seq 8149, type 65521, tkts 1 2012-06-12 22:27:00.931763 : GSIPC:RCVD: seq update (0.8148)->(0.8149) tp -15 fg 0x4 from 1 pbattr 0x0 2012-06-12 22:27:00.931779 : GSIPC:TKT: collect msg 0x7fa620af6490 from 1 for rcvr 0, tickets 1 2012-06-12 22:27:00.931794 : kjbrcvdscn[0x0.3f72dc][from 1][idx 2012-06-12 22:27:00.931810 : kjbrcvdscn[no bscn dd_master_inst_kjxmddi == 1 * kjddind: dump sgh: NXTIN (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 NXTOUT (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 2012-06-12 22:27:00.932058*: kjddind: req->timestamp [0.15], kjddt [0.15] 2012-06-12 22:27:00.932058*: >> DDmsg:KJX_DD_VALIDATE,TS[0.15],Inst 1->2,ddxid[id1,id2,inst:2097153,31,1],ddlock[0x95023930,829],ddMasterInst 1 2012-06-12 22:27:00.932058*: lock [(nil),0], op = [vald_dd] 2012-06-12 22:27:00.932058*: kjddind: updated local timestamp [0.15] * kjddind: case KJX_DD_VALIDATE *** 2012-06-12 22:27:00.932 * kjddvald called: kjxmddi stuff: * cont_lockp (nil) * dd_lockp 0x95023930 * dd_inst 1 * dd_master_inst 1 * sgh graph: NXTIN (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 NXTOUT (nil) 0 wq 0 cvtops x0 0x0.0x0(ext 0x0,0x0)[0000-0000-00000000] inst 1 POP WFG NODE: lock=(nil) * kjddvald: dump the PRQ: BLOCKER 0xbbb9a800 5 wq 1 cvtops x28 TX 0xe000c.0x32(ext 0x5,0x0)[20000-0002-00000022] inst 2 BLOCKED 0xbbce92f8 5 wq 2 cvtops x1 TX 0x80016.0x5d4(ext 0x2,0x0)[20000-0002-00000022] inst 2 * kjddvald: KJDD_NXTONOD ->node_kjddsg.dinst_kjddnd =1 * kjddvald: ... which is not my node, my subgraph is validated but the cycle is not complete Global blockers dump start:--------------------------------- DUMP LOCAL BLOCKER/HOLDER: block level 5 res [0x80016][0x5d4],[TX][ext 0x2,0x0] ??dead lock!!! ???????11.2.0.3???? RAC LMD???????????”_lm_dd_interval”????????????20s?  ???????10g?_lm_dd_interval???60s,??????Processes?????????????????,????????????Server Process????????60s??????11g?????(??????LMD???????)???????,???????????10s??? Enqueue Deadlock Detection? ?11g??? RAC?LMD???????hidden parameter ????”_lm_dd_interval”???,RAC????????????????,???????????: SQL> col name for a50 SQL> col describ for a60 SQL> col value for a20 SQL> set linesize 140 pagesize 1400 SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y 3 WHERE x.inst_id = USERENV ('Instance') 4 AND y.inst_id = USERENV ('Instance') 5 AND x.indx = y.indx 6 AND x.ksppinm like '_lm_dd%'; NAME VALUE DESCRIB -------------------------------------------------- -------------------- ------------------------------------------------------------ _lm_dd_interval 20 dd time interval in seconds _lm_dd_scan_interval 5 dd scan interval in seconds _lm_dd_search_cnt 3 number of dd search per token get _lm_dd_max_search_time 180 max dd search time per token _lm_dd_maxdump 50 max number of locks to be dumped during dd validation _lm_dd_ignore_nodd FALSE if TRUE nodeadlockwait/nodeadlockblock options are ignored 6 rows selected.

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• Keeping track of File System Utilization in Ops Center 12c

  - by S Stelting

  Enterprise Manager Ops Center 12c provides significant monitoring capabilities, combined with very flexible incident management. These capabilities even extend to monitoring the file systems associated with Solaris or Linux assets. Depending on your needs you can monitor and manage incidents, or you can fine tune alert monitoring rules to specific file systems. This article will show you how to use Ops Center 12c to Track file system utilization Adjust file system monitoring rules Disable file system rules Create custom monitoring rules If you're interested in this topic, please join us for a WebEx presentation! Date: Thursday, November 8, 2012 Time: 11:00 am, Eastern Standard Time (New York, GMT-05:00) Meeting Number: 598 796 842 Meeting Password: oracle123 To join the online meeting ------------------------------------------------------- 1. Go to https://oracleconferencing.webex.com/oracleconferencing/j.php?ED=209833597&UID=1512095432&PW=NOWQ3YjJlMmYy&RT=MiMxMQ%3D%3D 2. If requested, enter your name and email address. 3. If a password is required, enter the meeting password: oracle123 4. Click "Join". To view in other time zones or languages, please click the link: https://oracleconferencing.webex.com/oracleconferencing/j.php?ED=209833597&UID=1512095432&PW=NOWQ3YjJlMmYy&ORT=MiMxMQ%3D%3D   Monitoring File Systems for OS Assets The Libraries tab provides basic, device-level information about the storage associated with an OS instance. This tab shows you the local file system associated with the instance and any shared storage libraries mounted by Ops Center. More detailed information about file system storage is available under the Analytics tab under the sub-tab named Charts. Here, you can select and display the individual mount points of an OS, and export the utilization data if desired: In this example, the OS instance has a basic root file partition and several NFS directories. Each file system mount point can be independently chosen for display in the Ops Center chart. File Systems and Incident  Reporting Every asset managed by Ops Center has a "monitoring policy", which determines what represents a reportable issue with the asset. The policy is made up of a bunch of monitoring rules, where each rule describes An attribute to monitor The conditions which represent an issue The level or levels of severity for the issue When the conditions are met, Ops Center sends a notification and creates an incident. By default, OS instances have three monitoring rules associated with file systems: File System Reachability: Triggers an incident if a file system is not reachable NAS Library Status: Triggers an incident for a value of "WARNING" or "DEGRADED" for a NAS-based file system File System Used Space Percentage: Triggers an incident when file system utilization grows beyond defined thresholds You can view these rules in the Monitoring tab for an OS: Of course, the default monitoring rules is that they apply to every file system associated with an OS instance. As a result, any issue with NAS accessibility or disk utilization will trigger an incident. This can cause incidents for file systems to be reported multiple times if the same shared storage is used by many assets, as shown in this screen shot: Depending on the level of control you'd like, there are a number of ways to fine tune incident reporting. Note that any changes to an asset's monitoring policy will detach it from the default, creating a new monitoring policy for the asset. If you'd like, you can extract a monitoring policy from an asset, which allows you to save it and apply the customized monitoring profile to other OS assets. Solution #1: Modify the Reporting Thresholds In some cases, you may want to modify the basic conditions for incident reporting in your file system. The changes you make to a default monitoring rule will apply to all of the file systems associated with your operating system. Selecting the File Systems Used Space Percentage entry and clicking the "Edit Alert Monitoring Rule Parameters" button opens a pop-up dialog which allows you to modify the rule. The first screen lets you decide when you will check for file system usage, and how long you will wait before opening an incident in Ops Center. By default, Ops Center monitors continuously and reports disk utilization issues which exist for more than 15 minutes. The second screen lets you define actual threshold values. By default, Ops Center opens a Warning level incident is utilization rises above 80%, and a Critical level incident for utilization above 95% Solution #2: Disable Incident Reporting for File System If you'd rather not report file system incidents, you can disable the monitoring rules altogether. In this case, you can select the monitoring rules and click the "Disable Alert Monitoring Rule(s)" button to open the pop-up confirmation dialog. Like the first solution, this option affects all file system monitoring. It allows you to completely disable incident reporting for NAS library status or file system space consumption. Solution #3: Create New Monitoring Rules for Specific File Systems If you'd like to have the greatest flexibility when monitoring file systems, you can create entirely new rules. Clicking the "Add Alert Monitoring Rule" (the icon with the green plus sign) opens a wizard which allows you to define a new rule.  This rule will be based on a threshold, and will be used to monitor operating system assets. We'd like to add a rule to track disk utilization for a specific file system - the /nfs-guest directory. To do this, we specify the following attribute FileSystemUsages.name=/nfs-guest.usedSpacePercentage The value of name in the attribute allows us to define a specific NFS shared directory or file system... in the case of this OS, we could have chosen any of the values shown in the File Systems Utilization chart at the beginning of this article. usedSpacePercentage lets us define a threshold based on the percentage of total disk space used. There are a number of other values that we could use for threshold-based monitoring of FileSystemUsages, including freeSpace freeSpacePercentage totalSpace usedSpace usedSpacePercentage The final sections of the screen allow us to determine when to monitor for disk usage, and how long to wait after utilization reaches a threshold before creating an incident. The next screen lets us define the threshold values and severity levels for the monitoring rule: If historical data is available, Ops Center will display it in the screen. Clicking the Apply button will create the new monitoring rule and active it in your monitoring policy. If you combine this with one of the previous solutions, you can precisely define which file systems will generate incidents and notifications. For example, this monitoring policy has the default "File System Used Space Percentage" rule disabled, but the new rule reports ONLY on utilization for the /nfs-guest directory. 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• home page of my site is not appear in google search, when I type site:mario--games.com

  - by Bimal Das

  I am totally confused, when I place site:mario--games.com in google I see every page of my website in serp(search engine result page) except the home page. I don’t know why it’s happening but I check everything according to google SEO rule. But not getting success.I try to check my site through google webmaster tool everything is perfect there, Please help me to solve this. htaccess rule of my site RewriteEngine on #RewriteBase / #RewriteCond %{HTTP_REFERER} !^$ #RewriteCond %{HTTP_REFERER} !^http://(www\.)?jocuri-barbie.ro/.*$ [NC] #RewriteCond %{HTTP_REFERER} !^http://(www\.)?joc-jocuri-barbie.ro/.*$ [NC] #RewriteRule \.(gif|jpg|swf|flv|png)$ / [F] RewriteCond %{HTTP_HOST} ^sitename\.com$ RewriteRule ^(.*)$ http://www.sitename.com/$1 [R=301,L] RewriteRule ^privacy_policy.html$ privacy.php RewriteRule ^contact_us.html$ contact.php #RewriteCond %{HTTP_HOST} !^sitename.com$ #RewriteRule ^(.*)$ http://sitename.com/$1 [L,QSA,R=301] RewriteRule ^index\.php$ / [QSA,R=301] RewriteRule ^([A-Za-z0-9_]+)_([0-9]+).html$ articol.php?id=$2 RewriteRule ^([a-z_]+).html$ categorii.php?abbr=$1 RewriteRule ^([A-Za-z0-9+]+)$ search.php?cuvinte=$1 RewriteRule ^images/$ images [F] RewriteRule ^o_articole/$ o_articole [F]

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• Opening images sorted by modification date/size/type/etc.

  - by menino bolinho

  Suppose I have a folder with pictures in them. If I sort them by name once I open one with Image Viewer and navigate to the others the order is respected. But if I sort my files by modification date, for example, I can't do that. Basically, the default Image Viewer only lets you navigate images by name. According to this post on the ubuntuforums this has been an issue since 2007! Is there a good/easy way to fix it? Seems like such a trivial thing to me.

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• does ping command to a dns name uses DNS PTR type messages?

  - by TiagoM

  Okay I cant understand this, when I try to ping to a machine on my network using the name associated I get a response from that machine, thats normal.. But there are messages that the sender sends to the top machine (SOA) that I dont understand.. First he sends a type A and gets a response with the IP associated to the name used on the ping command, but after that.. the sender only sends (before each ping) messages of type PTR to the (SOA) Saying this: Standar query 0xf66c PTR 12.45.168.192.in-addr.arpa and SOA respond with: Standard query response 0xf66c No such name And before each ping they do this, I dont know why... I notice this using wireshark, thanks alot again for accept me here, being able to get some answer :)

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• home page of my site is not appear in google search, when I type site:example.com

  - by Bimal Das

  I am totally confused, when I place site:example.com in google I see every page of my website in serp(search engine result page) except the home page. I don’t know why it’s happening but I check everything according to google SEO rule. But not getting success.I try to check my site through google webmaster tool everything is perfect there, Please help me to solve this. htaccess rule of my site RewriteEngine on #RewriteBase / #RewriteCond %{HTTP_REFERER} !^$ #RewriteCond %{HTTP_REFERER} !^http://(www\.)?example.ro/.*$ [NC] #RewriteCond %{HTTP_REFERER} !^http://(www\.)?exa-example.ro/.*$ [NC] #RewriteRule \.(gif|jpg|swf|flv|png)$ / [F] RewriteCond %{HTTP_HOST} ^sitename\.com$ RewriteRule ^(.*)$ http://www.sitename.com/$1 [R=301,L] RewriteRule ^privacy_policy.html$ privacy.php RewriteRule ^contact_us.html$ contact.php #RewriteCond %{HTTP_HOST} !^sitename.com$ #RewriteRule ^(.*)$ http://sitename.com/$1 [L,QSA,R=301] RewriteRule ^index\.php$ / [QSA,R=301] RewriteRule ^([A-Za-z0-9_]+)_([0-9]+).html$ articol.php?id=$2 RewriteRule ^([a-z_]+).html$ categorii.php?abbr=$1 RewriteRule ^([A-Za-z0-9+]+)$ search.php?cuvinte=$1 RewriteRule ^images/$ images [F] RewriteRule ^o_articole/$ o_articole [F]

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• SQL SERVER – Capturing Wait Types and Wait Stats Information at Interval – Wait Type – Day 5 of 28

  - by pinaldave

  Earlier, I have tried to cover some important points about wait stats in detail. Here are some points that we had covered earlier. DMV related to wait stats reset when we reset SQL Server services DMV related to wait stats reset when we manually reset the wait types However, at times, there is a need of making this data persistent so that we can take a look at them later on. Sometimes, performance tuning experts do some modifications to the server and try to measure the wait stats at that point of time and after some duration. I use the following method to measure the wait stats over the time. -- Create Table CREATE TABLE [MyWaitStatTable]( [wait_type] [nvarchar](60) NOT NULL, [waiting_tasks_count] [bigint] NOT NULL, [wait_time_ms] [bigint] NOT NULL, [max_wait_time_ms] [bigint] NOT NULL, [signal_wait_time_ms] [bigint] NOT NULL, [CurrentDateTime] DATETIME NOT NULL, [Flag] INT ) GO -- Populate Table at Time 1 INSERT INTO MyWaitStatTable ([wait_type],[waiting_tasks_count],[wait_time_ms],[max_wait_time_ms],[signal_wait_time_ms], [CurrentDateTime],[Flag]) SELECT [wait_type],[waiting_tasks_count],[wait_time_ms],[max_wait_time_ms],[signal_wait_time_ms], GETDATE(), 1 FROM sys.dm_os_wait_stats GO ----- Desired Delay (for one hour) WAITFOR DELAY '01:00:00' -- Populate Table at Time 2 INSERT INTO MyWaitStatTable ([wait_type],[waiting_tasks_count],[wait_time_ms],[max_wait_time_ms],[signal_wait_time_ms], [CurrentDateTime],[Flag]) SELECT [wait_type],[waiting_tasks_count],[wait_time_ms],[max_wait_time_ms],[signal_wait_time_ms], GETDATE(), 2 FROM sys.dm_os_wait_stats GO -- Check the difference between Time 1 and Time 2 SELECT T1.wait_type, T1.wait_time_ms Original_WaitTime, T2.wait_time_ms LaterWaitTime, (T2.wait_time_ms - T1.wait_time_ms) DiffenceWaitTime FROM MyWaitStatTable T1 INNER JOIN MyWaitStatTable T2 ON T1.wait_type = T2.wait_type WHERE T2.wait_time_ms > T1.wait_time_ms AND T1.Flag = 1 AND T2.Flag = 2 ORDER BY DiffenceWaitTime DESC GO -- Clean up DROP TABLE MyWaitStatTable GO If you notice the script, I have used an additional column called flag. I use it to find out when I have captured the wait stats and then use it in my SELECT query to SELECT wait stats related to that time group. Many times, I select more than 5 or 6 different set of wait stats and I find this method very convenient to find the difference between wait stats. In a future blog post, we will talk about specific wait stats. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• Why does my custom Amazon EC2 AMI have limited instance type options?

  - by John

  The Basic 64-bit Amazon Linux AMI has the following instance type options available: Micro Large Extra-Large High-Memory Extra Large ... etc I booted up this AMI as a micro type, made customizations, shut it down, detached the volume, took a snapshot, and registered my own custom AMI: ec2-register –snapshot [snapshot_id] –description "my description" –name "my name" –kernel aki-427d952b That worked. HOWEVER, when I try to create an instance from my custom AMI, only the following instance types are available: Micro Small High-CPU Medium ... which coincidentally are the same instance types available if you try to boot up the 32-bit Amazon image. Why are the available instance types of my custom image varying from the available instance types of the image I based it off of?

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• Block IP Address including ICMP using UFW

  - by dr jimbob

  I prefer ufw to iptables for configuring my software firewall. After reading about this vulnerability also on askubuntu, I decided to block the fixed IP of the control server: 212.7.208.65. I don't think I'm vulnerable to this particular worm (and understand the IP could easily change), but wanted to answer this particular comment about how you would configure a firewall to block it. I planned on using: # sudo ufw deny to 212.7.208.65 # sudo ufw deny from 212.7.208.65 However as a test that the rules were working, I tried pinging after I setup the rules and saw that my default ufw settings let ICMP through even from an IP address set to REJECT or DENY. # ping 212.7.208.65 PING 212.7.208.65 (212.7.208.65) 56(84) bytes of data. 64 bytes from 212.7.208.65: icmp_seq=1 ttl=52 time=79.6 ms ^C --- 212.7.208.65 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 79.630/79.630/79.630/0.000 ms Now, I'm worried that my ICMP settings are too generous (conceivably this or a future worm could setup an ICMP tunnel to bypass my firewall rules). I believe this is the relevant part of my iptables rules is given below (and even though grep doesn't show it; the rules are associated with the chains shown): # sudo iptables -L -n | grep -E '(INPUT|user-input|before-input|icmp |212.7.208.65)' Chain INPUT (policy DROP) ufw-before-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-before-input (1 references) ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 8 ufw-user-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-user-input (1 references) DROP all -- 0.0.0.0/0 212.7.208.65 DROP all -- 212.7.208.65 0.0.0.0/0 How should I go about making it so ufw blocks ICMP when I specifically attempt to block an IP address? My /etc/ufw/before.rules has in part: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ACCEPT -A ufw-before-input -p icmp --icmp-type source-quench -j ACCEPT -A ufw-before-input -p icmp --icmp-type time-exceeded -j ACCEPT -A ufw-before-input -p icmp --icmp-type parameter-problem -j ACCEPT -A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT I'm tried changing ACCEPT above to ufw-user-input: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ufw-user-input -A ufw-before-input -p icmp --icmp-type source-quench -j ufw-user-input -A ufw-before-input -p icmp --icmp-type time-exceeded -j ufw-user-input -A ufw-before-input -p icmp --icmp-type parameter-problem -j ufw-user-input -A ufw-before-input -p icmp --icmp-type echo-request -j ufw-user-input But ufw wouldn't restart after that. I'm not sure why (still troubleshooting) and also not sure if this is sensible? Will there be any negative effects (besides forcing the software firewall to force ICMP through a few more rules)?

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• IDC Analyst Report Touts Oracle–Accenture Strategic Initiative

  - by kristin.jellison

  Hi there, partners! Oracle Engineered Systems have been getting some love lately, and we want to share it with you! The market intelligence and advisory firm IDC recently released a report lauding Oracle and Accenture’s strategic initiative to route the performance and flexibility of Oracle Engineered Systems to clients. The report, "Oracle and Accenture Strategic Alliance Places Big Bet on Engineered Systems,” by Steve White, reflects a largely positive analysis of the relationship. White notes that the alliance is “one of the largest in the industry.” Under the relationship, Accenture has incorporated Oracle Engineered Systems—including Oracle Exadata Database Machine, Oracle Exalogic Elastic Cloud, Oracle SuperCluster, and Oracle Exalytics In-Memory Machine—into its leading datacenter transformation consulting services. Together, the two companies have also created bespoke platforms, such as the Accenture Foundation Platform for Oracle, which helps clients accelerate deployments on Oracle Fusion Middleware, running Oracle Exalogic Elastic Cloud and Oracle Exadata Database Machine. Oracle Engineered Systems deliver a single, engineered platform—including server to storage and networking. This makes it easier and cheaper for Accenture clients around the world to prepare their datacenters for managing, processing and analyzing the massive amounts of data they (rightly) anticipate seeing in the next decade. The new solutions can help reduce the effort and cost to migrate any vendor database to an Oracle Engineered Systems platform, which can lower the cost of ownership by up to 50 percent. For its part, Accenture has built a team of 300 consultants to implement and increase the flexibility and stability of client datacenters. This move further expands one of the fastest-growing full-service Oracle Enterprise solutions. Over 52,000 Accenture consultants are qualified to implement, upgrade and outsource the Oracle product suite. Accenture is a Diamond-level member of Oracle PartnerNetwork (OPN). For Oracle Partners, this update should give you at least two things to walk away with. First, this initiative is showing signs of success. As Marty Cole, group chief executive for Accenture’s Technology growth platform, put it, “We are seeing an increasing number of clients recognizing the value of consolidating their databases and taking advantage of the cost and performance benefits delivered by these solutions.” The pipeline is there—and not just for Accenture. Use this example to show your clients that investments in Oracle Engineered Systems are on the rise. Second, recognize that Oracle Engineered Systems represent one of the biggest platforms for growth that Oracle has to offer partners. As part of the agreement, Accenture is able to provide: Platform Readiness Assessments Platform Implementation App Rationalization Database Rationalization Managed Services These are all enablement opportunities you can offer customers under Oracle’s partner programs —to continue building the value of their investments, and the value of your relationship with Oracle. Take a read through the IDC report. To learn more about the partnership, see this press release. Happy selling! The OPN Communications Team

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• Getting started with Document Set in SharePoint2010

  - by ybbest

  Folders are widely used in traditional file based system, in SharePoint world you can create folder in the document library as well. However, there is a new improved feature in SharePoint called Document Set; you can attach metadata to the document set. To get start with Document set, you can perforce the following steps. 1. Go to Site Settings >>Site collection features >>Activate the Document Sets feature. 2. After the Document Sets feature is activated, you will get a new content type called Document Set. 3. Next, we can create a custom content type called Loan Application Document Set that inherited from Document Set Content Type. 4. Then I create a new column called Application Number. 5. Add this field to the loan application content type 6. Create a new Content Type called Loan Contract form that inherited from Document content type. 7. Add the Application Number to the Loan Contract form content type. 8. Create a new Content Type called Loan Application form that inherited from Document content type and add Application Number to it.(The same step as above.) 9.Go to the Loan Application Document Set content type and go to the Document Set Settings. 10. You can define which content type you would like this Document set contains and you can also define the default document for each content type. When you create a new document set, those default documents will get automatically created in the document set. You can also define the Shared field that shared across content types; in my case I define the Application number and description as my shared fields. Finally, you can define the fields that you’d like to show in the document set welcome page. 11. Now create a new document library and attach those content types to the document library and create a new loan application document set. 12. You will see the default document created in the document set.If you updated Application Number on the document set , the field will get updated in the documents inside the document set as well.

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• With modern PC systems, what less-than-optimal designs have we inherited?

  - by Rob Kam

  What have been less than optimal design choices, that are now (almost) immutable features of the modern PC system, and what constraints led to these choices? There have been a great many of these. For example the qwerty keyboard is widespread although the Dvorak keyboard might be a better choice. I guess this is something to do with the teletypes that were used as early computer keyboards, which had originally been modified from typewriters.

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• Are virtualization softwares allow guest Operating Systems to fully utilize host's drivers?

  - by afriza

  I like to use linux distros except for the lack of drivers that can fully utilize the hardware. As an example, graphic card drivers for linux cannot perform equally with their windows' counterpart even if they are from the same vendor! Does using virtualization reduce this problem? Which virtualization technologies / softwares perform well for this case?

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• Does the type of prior employers matter when applying for a new job?

  - by Peter Smith

  Is there a bias in industry regarding the kind of previous employers an applicant has had (Government contractors, researchers, small business, large corporations)? I'm currently working for a University as a generalist programmer and I like my job here. But I'm worried that if I had to switch jobs down the road and apply for a corporate job that my resume would be dismissed based on the fact that I'm working in academia.

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• How do I get a file type to show up with a name I choose in Windows Explorer?

  - by Adrian

  I associated a file extension using the command assoc. But in the Explorer, it lists the type as the extension name. I.e. assoc .sh=ShellScript will still cause explorer to show the type as SH File. Anyway to change it so it shows up as ShellScript or better yet, Shell Script? EDIT: Using assoc didn't work. Seems to be something wrong with my registry. I figured that using quotes would put in a white space, but because it didn't show up in the explorer, I figured it may have been part of the problem.

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• Windows.Threading.Dispatcher' does not contain a definition for 'RunAsync' and no extension method 'RunAsync' accepting a first argument of type

  - by suhail mehdi

  public MainPage() { InitializeComponent(); offline.Visibility = (Network.IsConnected ? Visibility.Collapsed : Visibility.Visible); Network.InternetConnectionChanged += async (s, e) => { await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { offline.Visibility = (e.IsConnected ? Visibility.Collapsed : Visibility.Visible); }); }; }

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• creating a simulation game, what type of knowledge is needed? [closed]

  - by Jordan

  I am a beginner in game development. As a part of learning and fun, want to create a game in java-script and html5. I am planning a game that we were used to play in childhood, that is "new business"- a monopoly game, in that we used to buy ,rent,sell places and bank we get some money to play and etc. are features. Its just simple ludo like game. So can anyone suggest me from where to start? what will be the designing? Is it possible to create it only in a html5 and java-script.

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• Should *'s go next to the type or the variable name? [closed]

  - by derekerdmann

  Possible Duplicate: int* i; or int *i; or int * i; When working in C or C++, how should pointers be declared? Like this: char* derp; or this: char *derp; I typically use the first method, because the variable is a character pointer, but I know that it can create confusion when declaring multiple variables at once: char* herp, derp; herp becomes a character pointer, while derp is just a character. I know it often comes down to coding style, but which one is "better?" Should I sacrifice clarity to eliminate potential confusion?

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• MiniMax function throws null pointer exception

  - by Sven

  I'm working on a school project, I have to build a tic tac toe game with the AI based on the MiniMax algorithm. The two player mode works like it should. I followed the code example on http://ethangunderson.com/blog/minimax-algorithm-in-c/. The only thing is that I get a NullPointer Exception when I run the code. And I can't wrap my finger around it. I placed a comment in the code where the exception is thrown. The recursive call is returning a null pointer, what is very strange because it can't.. When I place a breakpoint on the null return with the help of a if statement, then I see that there ARE still 2 to 3 empty places.. I probably overlooking something. Hope someone can tell me what I'm doing wrong. Here is the MiniMax code (the tic tac toe code is not important): /* * To change this template, choose Tools | Templates * and open the template in the editor. */ package MiniMax; import Game.Block; import Game.Board; import java.util.ArrayList; public class MiniMax { public static Place getBestMove(Board gameBoard, Block.TYPE player) { Place bestPlace = null; ArrayList<Place> emptyPlaces = gameBoard.getEmptyPlaces(); Board newBoard; //loop trough all the empty places for(Place emptyPlace : emptyPlaces) { newBoard = gameBoard.clone(); newBoard.setBlock(emptyPlace.getRow(), emptyPlace.getCell(), player); //no game won and still room to move if(newBoard.getWinner() == Block.TYPE.NONE && newBoard.getEmptyPlaces().size() > 0) { //is an node (has children) Place tempPlace = getBestMove(newBoard, invertPlayer(player)); //ERROR is thrown here! tempPlace is null. emptyPlace.setScore(tempPlace.getScore()); } else { //is an leaf if(newBoard.getWinner() == Block.TYPE.NONE) { emptyPlace.setScore(0); } else if(newBoard.getWinner() == Block.TYPE.X) { emptyPlace.setScore(-1); } else if(newBoard.getWinner() == Block.TYPE.O) { emptyPlace.setScore(1); } //if this move is better then our prev move, take it! if((bestPlace == null) || (player == Block.TYPE.X && emptyPlace.getScore() < bestPlace.getScore()) || (player == Block.TYPE.O && emptyPlace.getScore() > bestPlace.getScore())) { bestPlace = emptyPlace; } } } //This should never be null, but it does.. return bestPlace; } private static Block.TYPE invertPlayer(Block.TYPE player) { if(player == Block.TYPE.X) { return Block.TYPE.O; } return Block.TYPE.X; } }

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• Subterranean IL: Generics and array covariance

  - by Simon Cooper

  Arrays in .NET are curious beasts. They are the only built-in collection types in the CLR, and SZ-arrays (single dimension, zero-indexed) have their own commands and IL syntax. One of their stranger properties is they have a kind of built-in covariance long before generic variance was added in .NET 4. However, this causes a subtle but important problem with generics. First of all, we need to briefly recap on array covariance. SZ-array covariance To demonstrate, I'll tweak the classes I introduced in my previous posts: public class IncrementableClass { public int Value; public virtual void Increment(int incrementBy) { Value += incrementBy; } } public class IncrementableClassx2 : IncrementableClass { public override void Increment(int incrementBy) { base.Increment(incrementBy); base.Increment(incrementBy); } } In the CLR, SZ-arrays of reference types are implicitly convertible to arrays of the element's supertypes, all the way up to object (note that this does not apply to value types). That is, an instance of IncrementableClassx2[] can be used wherever a IncrementableClass[] or object[] is required. When an SZ-array could be used in this fashion, a run-time type check is performed when you try to insert an object into the array to make sure you're not trying to insert an instance of IncrementableClass into an IncrementableClassx2[]. This check means that the following code will compile fine but will fail at run-time: IncrementableClass[] array = new IncrementableClassx2[1]; array[0] = new IncrementableClass(); // throws ArrayTypeMismatchException These checks are enforced by the various stelem* and ldelem* il instructions in such a way as to ensure you can't insert a IncrementableClass into a IncrementableClassx2[]. For the rest of this post, however, I'm going to concentrate on the ldelema instruction. ldelema This instruction pops the array index (int32) and array reference (O) off the stack, and pushes a pointer (&) to the corresponding array element. However, unlike the ldelem instruction, the instruction's type argument must match the run-time array type exactly. This is because, once you've got a managed pointer, you can use that pointer to both load and store values in that array element using the ldind* and stind* (load/store indirect) instructions. As the same pointer can be used for both input and output to the array, the type argument to ldelema must be invariant. At the time, this was a perfectly reasonable restriction, and maintained array type-safety within managed code. However, along came generics, and with it the constrained callvirt instruction. So, what happens when we combine array covariance and constrained callvirt? .method public static void CallIncrementArrayValue() { // IncrementableClassx2[] arr = new IncrementableClassx2[1] ldc.i4.1 newarr IncrementableClassx2 // arr[0] = new IncrementableClassx2(); dup newobj instance void IncrementableClassx2::.ctor() ldc.i4.0 stelem.ref // IncrementArrayValue<IncrementableClass>(arr, 0) // here, we're treating an IncrementableClassx2[] as IncrementableClass[] dup ldc.i4.0 call void IncrementArrayValue<class IncrementableClass>(!!0[],int32) // ... ret } .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } And the result: Unhandled Exception: System.ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array. at IncrementArrayValue[T](T[] arr, Int32 index) at CallIncrementArrayValue() Hmm. We're instantiating the generic method as IncrementArrayValue<IncrementableClass>, but passing in an IncrementableClassx2[], hence the ldelema instruction is failing as it's expecting an IncrementableClass[]. On features and feature conflicts What we've got here is a conflict between existing behaviour (ldelema ensuring type safety on covariant arrays) and new behaviour (managed pointers to object references used for every constrained callvirt on generic type instances). And, although this is an edge case, there is no general workaround. The generic method could be hidden behind several layers of assemblies, wrappers and interfaces that make it a requirement to use array covariance when calling the generic method. Furthermore, this will only fail at runtime, whereas compile-time safety is what generics were designed for! The solution is the readonly. prefix instruction. This modifies the ldelema instruction to ignore the exact type check for arrays of reference types, and so it lets us take the address of array elements using a covariant type to the actual run-time type of the array: .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 readonly. ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } But what about type safety? In return for ignoring the type check, the resulting controlled mutability pointer can only be used in the following situations: As the object parameter to ldfld, ldflda, stfld, call and constrained callvirt instructions As the pointer parameter to ldobj or ldind* As the source parameter to cpobj In other words, the only operations allowed are those that read from the pointer; stind* and similar that alter the pointer itself are banned. This ensures that the array element we're pointing to won't be changed to anything untoward, and so type safety within the array is maintained. This is a typical example of the maxim that whenever you add a feature to a program, you have to consider how that feature interacts with every single one of the existing features. Although an edge case, the readonly. prefix instruction ensures that generics and array covariance work together and that compile-time type safety is maintained. Tune in next time for a look at the .ctor generic type constraint, and what it means.

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