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• xorg, nvidia, log-in all hosed - how can I completely reset graphics set-up/settings?

  - by Fred Hamilton

  I just did a fresh install of Mythbuntu 12.04.1 on my Intel MB with nVidia 9500GT graphics card. Hardware's been working great with 10.10 for about 2 years. Background: (optional - feel free to skip to question) I was trying to get my component video output to generate 720p, messing around with the nvidia drivers, and now the entire display system is hosed. I can SSH in and get a terminal. Depending on which nvidia package I install/remove, I get: Garbage on screen (after I "apt-get remove nvidia*") A low-res graphical log-in screen where I can log in as fred or guest. If I log in as fred, it displays some text mode status line then goes right back to the log-in screen. If I log in as guest, I actually get the full Ubuntu desktop, but I need to be able to log in as fred. Other times I get an error: "API mismatch: the NVIDIA kernel module has version 304.43, but this NVIDIA driver component has version 295.49." I've googled around, including trying this thread with the same error message, but to no effect. Question: How can I just reset x settings, drivers, everything display-related to the exact same way it was after a fresh install?

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• ntop to analyse bandwidth usage on multiple ASA 5505

  - by dunxd

  I have set up a netflow server at our data centre, which is connected via VPN to ~40 remote offices using Cisco ASA 5505. The aim is to analyse usage data and find out exactly how the remote connections are being used. I followed through http://techowto.files.wordpress.com/2008/09/ntop-guide.pdf to set up ntop and https://supportforums.cisco.com/docs/DOC-6114 to set up the ASAs. I can see from the Plugin Netflow Statistics page that netflow packets from my ASAs are being received - the counter is increasing. However, I am not seeing any breakdown on the Global Traffic Statistic page after switching to the Netflow interface. I'm just seeing a pie chart showing 100% traffic for eth0. The interfaces and documentation are a little hard to follow so I am not sure I have got things configured correctly. When setting up my NetFlow-device.2 I can specify Virtual NetFlow Interface Network Address - the web UI says This value is in the form of a network address and mask on the network where the actual NetFlow probe is located. is this a Network address (e.g. 192.168.0.0/24) or an actual host IP address (192.167.0.1/24)? If that should be a network address, is this the network in which one of my ASAs is or the network in which my ntop server is? If a host IP address, is this the IP address used by eth0 on my ntop server, the IP address of an ASA, or something else? Do I need a separate virtual interface for each ASA I am collecting netflow data from? Any guidance would be greatly welcome.

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• Java stored procedures in Oracle, a good idea?

  - by Scott A

  I'm considering using a Java stored procedure as a very small shim to allow UDP communication from a PL/SQL package. Oracle does not provide a UTL_UDP to match its UTL_TCP. There is a 3rd party XUTL_UDP that uses Java, but it's closed source (meaning I can't see how it's implemented, not that I don't want to use closed source). An important distinction between PL/SQL and Java stored procedures with regards to networking: PL/SQL sockets are closed when dbms_session.reset_package is called, but Java sockets are not. So if you want to keep a socket open to avoid the tear-down/reconnect costs, you can't do it in sessions that are using reset_package (like mod_plsql or mod_owa HTTP requests). I haven't used Java stored procedures in a production capacity in Oracle before. This is a very large, heavily-used database, and this particular shim would be heavily used as well (it serves as a UDP bridge between a PL/SQL RFC 5424 syslog client and the local rsyslog daemon). Am I opening myself up for woe and horror, or are Java stored procedures stable and robust enough for usage in 10g? I'm wondering about issues with the embedded JVM, the jit, garbage collection, or other things that might impact a heavily used database.

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• Getting a lot of postmaster undeliverable notices for non-existent users

  - by Mike Walsh

  I've had my domain (straightpathsql.com) for a few years now. I host my e-mail with Google Accounts for business and have for awhile. ALl of the sudden in the past week I am starting to get a lot of postmaster delivery fail notices from various domains, most of them involving bogus e-mail addresses at my domain ([email protected], for example)... My assumption here is that someone is trying to relay on some other host (not my hosts which are secure through google apps for business, I presume) and there isn't much I can do to stop it. But I just want to make sure there isn't something else I need to be looking at here.. An example delivery fail notice is below.. I know nothing of those addresses below and they look like garbage... (Quick edit: the reason I get these messages is I set myself up as a catch all, so it doesn't matter what e-mail you send a note to at my domain, I'll get it if the account isn't setup... All of the failure messages are sent to bogus addresses on my domain) The following message to <[email protected]> was undeliverable. The reason for the problem: 5.1.0 - Unknown address error 553-'sorry, this recipient is in my badrecipientto list (#5.7.1)' Final-Recipient: rfc822;[email protected] Action: failed Status: 5.0.0 (permanent failure) Remote-MTA: dns; [118.82.83.11] Diagnostic-Code: smtp; 5.1.0 - Unknown address error 553-'sorry, this recipient is in my badrecipientto list (#5.7.1)' (delivery attempts: 0) ---------- Forwarded message ---------- From: Howard Blankenship <[email protected]> To: omiivi2922 <[email protected]> Cc: Date: Subject: Hi omiivi2922

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• Cisco Router - Add a missing MIB file

  - by Jonathan Rioux

  I have a Cisco 881w, and I would like to setup NBAR in my NetFlow Analyzer. But it says that my router misses this MIB in order to allow NFA to poll the router with snmp to get NBAR infos. From the FAQ page of the NetFlow Analyzer website, it responds to my error: Q. I am able to issue the command "ip nbar protocol-discovery" on the router and see the results. But NFA says my router does not support NBAR, Why? A. Earlier version of IOS supports NBAR discovery only on router. So you can very well execute the command "ip nbar protocol-discovery" on the router and see the results. But NBAR Protocol Discovery MIB(CISCO-NBAR-PROTOCOL-DISCOVERY-MIB) support came only on later releases. This is needed for collecting data via SNMP. Please verify that whether your router IOS supports CISCO-NBAR-PROTOCOL-DISCOVERY-MIB. The missing MIB is: CISCO-NBAR-PROTOCOL-DISCOVERY-MIB I found it here: ftp://ftp.cisco.com/pub/mibs/v2/CISCO-NBAR-PROTOCOL-DISCOVERY-MIB.my But how can I add this MIB into the router? The IOS of my router is: c880data-universalk9-mz.151-3.T1.bin

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• Quick Question, robots.txt Disallow: /*/ does what exactly?

  - by Exit

  A SEO firm suggested changing the robots.txt to: User-agent: * Disallow: /*/ Allow: /ims/ I'm not sure what that would do, but my guess is that is would tell all robots to index nothing but the ims folder. I understand the wildcard, but I'm confused by the slashes and don't know how they would play out in conjunction with the wildcard. * Update * I didn't mention that there is a sitemap listed in the robots.txt file, but according to one tech blogger, he realized that sitemaps trump robots exclusions. So, even though this says in Google Webmaster Tools that everything with a trailing slash will not be indexed, the sitemap contains the important links. I did notice that the link count on Google went from 360 to 336, and the sitemap links under the URL scaled back to 3 from 6. I'm not sure the cause or what links were removed, though. Perhaps it cleaned out garbage. I'm still clueless why they would add in 'Allow: /ims/', that seems pointless. And a quick list of what would index according to the robots rules above (withouth the sitemap) using /*/: domain.com Indexed domain.com/page.html Indexed domain.com/folder/ Not Indexed domain.com/folder/page.html Not Indexed

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• Vector with Constant-Time Remove - still a Vector?

  - by Darrel Hoffman

  One of the drawbacks of most common implementations of the Vector class (or ArrayList, etc. Basically any array-backed expandable list class) is that their remove() operation generally operates in linear time - if you remove an element, you must shift all elements after it one space back to keep the data contiguous. But what if you're using a Vector just to be a list-of-things, where the order of the things is irrelevant? In this case removal can be accomplished in a few simple steps: Swap element to be removed with the last element in the array Reduce size field by 1. (No need to re-allocate the array, as the deleted item is now beyond the size field and thus not "in" the list any more. The next add() will just overwrite it.) (optional) Delete last element to free up its memory. (Not needed in garbage-collected languages.) This is clearly now a constant-time operation, since only performs a single swap regardless of size. The downside is of course that it changes the order of the data, but if you don't care about the order, that's not a problem. Could this still be called a Vector? Or is it something different? It has some things in common with "Set" classes in that the order is irrelevant, but unlike a Set it can store duplicate values. (Also most Set classes I know of are backed by a tree or hash map rather than an array.) It also bears some similarity to Heap classes, although without the log(N) percolate steps since we don't care about the order.

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• CheckMemoryAllocationGame Sample

  - by Michael B. McLaughlin

  Many times I’ve found myself wondering how much GC memory some operation allocates. This is primarily in the context of XNA games due to the desire to avoid generating garbage and thus triggering a GC collection. Many times I’ve written simple programs to check allocations. I did it again recently. It occurred to me that many XNA developers find themselves asking this question from time to time. So I cleaned up my sample and published it on my website. Feel free to download it and put it to use. It’s rather thoroughly commented. The location where you insert the code you wish to check is in the Update method found in Game1.cs. The default that I put in is a line of code that generates a new Guid using Guid.NewGuid (which, if you’re curious, does not create any heap allocations). Read all of the comments in the Update method (at the very least) to make sure that your code is measured properly. It’s important to make sure that you meaningfully reference any thing you create after the second call to get the memory or else (in Release configuration at least) you will likely get incorrect results. Anyway, it should make sense when you read the comments and if not, feel free to post a comment here or ask me on Twitter. You can find my utilities and code samples page here: http://www.bobtacoindustries.com/developers/utils/Default.aspx To download CheckMemoryAllocationGame’s source code directly: http://www.bobtacoindustries.com/developers/utils/CheckMemoryAllocationGame.zip (If you’re looking to do this outside of the context of an XNA game, the measurement code in the Update method can easily be adapted into, e.g., a C# Windows Console application. In the past I mostly did that, actually. But I didn’t feel like adding references to all the XNA assemblies this time and… anyway, if you want you can easily convert it to a console application. If there’s any demand for it, I’ll do it myself and update this post when I get a chance.)

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• the OpenJDK group at Oracle is growing

  - by john.rose

  p.p1 {margin: 0.0px 0.0px 12.0px 0.0px; font: 12.0px Times} span.s1 {text-decoration: underline ; color: #0000ee} The OpenJDK software development team at Oracle is hiring. To get an idea of what we’re looking for, go to the Oracle recruitment portal and enter the Keywords “Java Platform Group” and the Location Keywords “Santa Clara”.  (We are a global engineering group based in Santa Clara.)  It’s pretty obvious what we are working on; just dive into a public OpenJDK repository or OpenJDK mailing list. Here is a typical job description from the current crop of requisitions: The Java Platform group is looking for an experienced, passionate and highly-motivated Software Engineer to join our world class development effort. Our team is responsible for delivering the Java Virtual Machine that is used by millions of developers. We are looking for a development engineer with a strong technical background and thorough understanding of the Java Virtual Machine, Java execution runtime, classloading, garbage collection, JIT compiler, serviceability and a desire to drive innovations. As a member of the software engineering division, you will take an active role in the definition and evolution of standard practices and procedures. You will be responsible for defining and developing software for tasks associated with the developing, designing and debugging of software applications or operating systems. Work is non-routine and very complex, involving the application of advanced technical/business skills in area of specialization. Leading contributor individually and as a team member, providing direction and mentoring to others. BS or MS degree or equivalent experience relevant to functional area. 7 years of software engineering or related experience.

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• Input Handling and Game loop

  - by Bob Coder

  So, I intercept the WM_KEYDOWN and other messages. Thing is, my game can't/shouldn't react to these messages just yet, since my game might be currently drawing to the screen or in the middle of updating my game entities. So the idea is to keep a keyboardstate and mousestate, which is updated by the part of my code that intercepts the windows messages. These states just keep track of which keys/buttons are currently pressed. Then, at the start of my game's update function, I access these keyboard and mouse states and my game reacts to the user input. Now, which is the best way to access these states? I assume that windows messages can be sent whenever, so the keyboard/mouse states are constantly being edited. Accessing say a list of currently pressed keys in the keyboard state the same time another part of the code is editing the list would cause problems. Should I make a deep copy of a state and act on that? How would I deal with the garbage generated though, this would take place every frame.

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• C Programming matrix

  - by Bilal Khan

  In this program the user enters the # of columns of the matrix and then the entries of the matrix. So, for example, if the user enters 2 for column # and 1 2 3 4 for entries then the program develops a 2 by 2 matrix with 1 2 3 4 as entries. My program works perfectly in such a case. However, if the user for example had only entered 1 2 3 then my program makes a matrix with garbage values. I would like the program in such a case to exit the program. It is a simple question, but it has me baffled. #include<stdio.h> #include<stdlib.h> int main() { int m,x, n, c = 0, d,k, matrix[10][10], transpose[10][10], product[10][10]; printf("Enter the number of columns of matrix "); scanf("%d",&m); if(m<=0){ printf("You entered a invalid value."); exit(0); } else{ printf("Enter the elements of matrix \n"); for( c = 0 ; c < 10 ; c++ ) { for( d = 0 ; d < m ; d++ ) { scanf("%d",&matrix[c][d]); if (matrix[c][d] == 99) // 'x' is character variable I declared to use as a break break; // c = c+1; } if (matrix[c][d] == 99) break; } } printf("\nHere is your matrix:\n"); int i; for(i=0;i<c;i++) { for(d=0;d<m;d++) { printf("%3d ",matrix[i][d]); } printf("\n"); }

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• How do I collect SNMP readings from intermittently-connected sites?

  - by Luke404

  I am collecting SNMP data on-site for a number of systems, currently using Cacti. These systems are spread on a number of sites that aren't always connected to internet, but I also need to centralize the data on a single system (datacenter housed server) and get graphs out of it. If I directly poll remote systems with a centralized Cacti I'd loose data when a site is not connected to internet. I should record data on-site (I have a server at each site and I can run whatever I want on it) and then 'sync' everything to the central system. One hack could be a cacti or directly an rrdtool on site and then periodically rsync RRD data to the central Cacti system, but that doesn't sound like a 'clean' solution: every RRD would have to be defined at both places and rsync scripts setup with the specific file names. Can you suggest a better solution? Cacti is not a requirement but I'd like to use something like that on the central system. On-site systems need only to collect data I don't need to graph it there or manage users rights to view data and stuff like that, users will only access the centralized system.

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• Google+ Platform Office Hours for June 13th, 2012

  Google+ Platform Office Hours for June 13th, 2012 Here are the show notes for this week's office hours. This week was devoted to your questions and our answers. We covered a wide breadth of topics. 0:43 - Introductions 2:54 - About Tabletop Forge's KickStarter - goo.gl 10:00 - Can I run multiple Hangout Apps at the same time? 12:28 - Is Google looking into adding more powerful Hangout moderation controls? 13:47 - How do you use Hangout Apps with Hangouts on Air? - +Fraser Cain's tips and tricks for Hangouts on Air: goo.gl 23:40 - I have an Android game. How do I port it to the Hangouts API? 27:57 - Pre-hangout Apps, Hangouts on Air pre-rolls, scheduling hangouts and other ways to help viewers find your Hangouts on Air 33:55 - How do I bookmark useful Google+ posts with Google+? 38:13 - Can you add a host ID field to the Hangouts API? When will the overlay garbage collection improve? 40:17 - Hand movement tracking as part of the Hangouts API Thanks to everyone who joined the hangout and asked questions on Google+! From: GoogleDevelopers Views: 698 18 ratings Time: 44:16 More in Science & Technology

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• Analyzing Memory Usage: Java vs C++ Negligible?

  - by Anthony

  How does the memory usage of an integer object written in Java compare\contrast with the memory usage of a integer object written in C++? Is the difference negligible? No difference? A big difference? I'm guessing it's the same because an int is an int regardless of the language (?) The reason why I asked this is because I was reading about the importance of knowing when a program's memory requirements will prevent the programmer from solving a given problem. What fascinated me is the amount of memory required for creating a single Java object. Take for example, an integer object. Correct me if I'm wrong but a Java integer object requires 24 bytes of memory: 4 bytes for its int instance variable 16 bytes of overhead (reference to the object's class, garbage collection info & synchronization info) 4 bytes of padding As another example, a Java array (which is implemented as an object) requires 48+bytes: 24 bytes of header info 16 bytes of object overhead 4 bytes for length 4 bytes for padding plus the memory needed to store the values How do these memory usages compare with the same code written in C++? I used to be oblivious about the memory usage of the C++ and Java programs I wrote, but now that I'm beginning to learn about algorithms, I'm having a greater appreciation for the computer's resources.

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• EXCEL workbook, intermitently, takes 30 seconds to load

  - by Julio Nobre

  I am trying to figure out why a simple .XLS EXCEL workbook is taking, randomly, 30 seconds to open. Before answering: Please, bear mind the following: Problem symptoms Hanging is intermitent and it takes exactly 30 seconds; During hanging there is no cpu or disk activity; It only happens during workbook load. Every runs smooth after that; Windows Explorer.exe hangs on folder, but all other folders, system and applications are still responsive; There are no consecutive hangings. I have to wait for while to reproduce this behaviour; All workbooks where located on a local drive (C:\BPI); The workbook has no macros and no addins; Office 2003 is being used for several years; The computer is running Windows XP; Computer has several network mapped drives, all addressed to main file server; Recently, main fileserver was replaced by Windows 2011 SBS Standard Edition What I have done so far I have traced machine Explorer.exe, using Process Monitor, added Duration column, and filtered by Duration 1. That's is how I found that hanging was taking exactly 30 seconds. For further information, please refer to Oliver Salzburg tutorial. Using Process Monitor, I have also figured out than five operations were taking most of sample collecting duration. Looking at sample image below, column Operation below you will notice that one single operation was taking 29 seconds; I have tried different workbooks (all of them smaller than 30 KB); I have, temporarily, removed all shortcuts on User Document's folder that were pointing to network drives or shares; I have runned CCleaner to fix registry issues; I made sure that there were no external links on tested workbooks; I have reproduced this behaviour for hours; I have extensivelly researched for hours on the web; Process Monitor's collected and filtered data

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• Does immutability entirely eliminate the need for locks in multi-processor programming?

  - by GlenPeterson

  Part 1 Clearly Immutability minimizes the need for locks in multi-processor programming, but does it eliminate that need, or are there instances where immutability alone is not enough? It seems to me that you can only defer processing and encapsulate state so long before most programs have to actually DO something. If a program performs actions on multiple processors, something needs to collect and aggregate the results. All this involves multi-process communication before, after, and possibly during some transformations. The start and end state of the machines are different. Can this always be done with no locks just by throwing out each object and creating a new one instead of changing the original (a crude view of immutability)? What cases still require locking? I'm interested in both the theoretical/academic answer and the practical/real-world answer. I know a lot of functional programmers like to talk about "no side effect" but in the "real world" everything has a side effect. Every processor click takes time and electricity and machine resources away from other processes. So I understand that there may be more than one perspective to answer this question from. If immutability is safe, given certain bounds or assumptions, I want to know what the borders of the "safety zone" are exactly. Some examples of possible boundaries: I/O Exceptions/errors Interfaces with programs written in other languages Interfaces with other machines (physical, virtual, or theoretical) Special thanks to @JimmaHoffa for his comment which started this question! Part 2 Multi-processor programming is often used as an optimization technique - to make some code run faster. When is it faster to use locks vs. immutable objects? Given the limits set out in Amdahl's Law, when can you achieve better over-all performance (with or without the garbage collector taken into account) with immutable objects vs. locking mutable ones? Summary I'm combining these two questions into one to try to get at where the bounding box is for Immutability as a solution to threading problems.

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• C++ Iterator lifetime and detecting invalidation

  - by DK.

  Based on what's considered idiomatic in C++11: should an iterator into a custom container survive the container itself being destroyed? should it be possible to detect when an iterator becomes invalidated? are the above conditional on "debug builds" in practice? Details: I've recently been brushing up on my C++ and learning my way around C++11. As part of that, I've been writing an idiomatic wrapper around the uriparser library. Part of this is wrapping the linked list representation of parsed path components. I'm looking for advice on what's idiomatic for containers. One thing that worries me, coming most recently from garbage-collected languages, is ensuring that random objects don't just go disappearing on users if they make a mistake regarding lifetimes. To account for this, both the PathList container and its iterators keep a shared_ptr to the actual internal state object. This ensures that as long as anything pointing into that data exists, so does the data. However, looking at the STL (and lots of searching), it doesn't look like C++ containers guarantee this. I have this horrible suspicion that the expectation is to just let containers be destroyed, invalidating any iterators along with it. std::vector certainly seems to let iterators get invalidated and still (incorrectly) function. What I want to know is: what is expected from "good"/idiomatic C++11 code? Given the shiny new smart pointers, it seems kind of strange that STL allows you to easily blow your legs off by accidentally leaking an iterator. Is using shared_ptr to the backing data an unnecessary inefficiency, a good idea for debugging or something expected that STL just doesn't do? (I'm hoping that grounding this to "idiomatic C++11" avoids charges of subjectivity...)

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• Installing Ubuntu 12.04 on a single GPT SSD which contains Windows 7

  - by Gary

  I recently bought a brand new 64 bit PC with a (ASUS) motherboard that supports UEFI and a GPT formatted 240Gb SSD, which contains Windows 7 in the first of 3 (80Gb) partitions. When the system arrived, it booted into Windows 7 like a dream, with no problems. I did not originally want Windows, but the manufacturer does not work with Linux (of any flavour), so I thought I would install Ubuntu into the second partition and dual boot. I downloaded the 12.04 64bit version and proceeded to install. Having selected to 'install', the screen became corrupted, with multicoloured garbage across the middle third of the screen !! So, I rebooted and --- MISSING OPERATING SYSTEM !!! The only way I can now get into Windows is via Super Grub2. First question - what went wrong ? 2nd - Will Ubuntu install on a GPT disk partition ? 3rd - Will it install alongside Windows 7 without screwing the boot mechanism ? 4th - How do I do it ? I have scoured the internet looking for appropriate answers and found NONE ! Please help.......

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• Multiple munin-nodes per machine

  - by Alexander T

  I'm collecting statistics remotely through JMX. The munin JMX plugin allows you to select an URL to connect to when aggregating statistics. This allows me to collect statistics from hosts which do not actually have munin-node installed. I find this a desirable property for some systems where I am hindered to install munin-node. How I work today is that if i want to collect JMX stats from machine A without munin-node, I install munin-node on machine B. Machine B then collects data from A via JMX, and reports it to munin-server, which runs on machine C. This setup requires multiple B-type machines: one per C-type machine. I would like to avoid this and instead use only one B-type machine to collect the data from all A-type machines and reports it to the only munin-server (C-type machine). As far as I understand this requires running multiple munin-nodes on B or in some other way report to munin-server that the B-type machine is reporting data from multiple sources. Is this possible? Thank you.

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• Ubuntu 12.04 using b43-fwcutter

  - by Nathan

  I have used 10.04 with the b43-fwcutter driver to drive my BCM4318 Broadcom card (a Linksys WPC54G v3) on my old Dell Inspiron 8100 for two years+ with no troubles. I just upgraded to 12.04 and although everything worked fine after install, before I added the b43-fwcutter driver, once I installed the driver, the system refuses to boot. Even before I install the Linksys card!! It just hangs on boot with graphical garbage on the screen. I tried several attempts to recover the system using the live CD, and finally reinstalled completely. I have been thru the cycle, install fresh system, verify everything works, then install b43-fwcutter and it is hung, several times. Consistent hard fail. The system runs fine on hardwire Ethernet, and wireless was fine on 10.04. But I cannot get there with 12.04. So after several attempts, I am now ready to admit defeat and ask for help. I have read every thread that search turned up, and either the advice is to do what I did, i.e. install fwcutter, or does not apply (Different Broadcom, STA, legacy, whatever) So what do I need to do to fix it? Or is the B43-fwcutter driver broken for 12.04? Thoughts? Tips? Log files needed??

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• Best way to troubleshoot intermittent network outages?

  - by Ben Scheirman

  We have a Comcast 50/10 line into our office. We keep seeing very short but sometimes frequent drops in our internet service. It's enough to kick you off of skype and stop any websites from loading, which is obviously affecting our productivity. We've tried 4 different routers, we've tried moving everyone off of wireless and onto wired via a switch and so far nothing has helped. Right now we're on a Cisco SB WRP400-G1 router. Attached to the router is a 16 port switch going to the ports in all of the offices. We've moved to OpenDNS in the case that it was the comcast DNS servers going down. Today we tried putting the modem, router, and switch on a UPS to make sure it wasn't power fluctuations that was causing it. Every time we call Comcast, by the time they are here the internet is working fine. I'd like to somehow prove that the problem is with Comcast, so if that means plugging in a machine directly into their router and collecting data all day, I'm up for that. I just want to hear ideas on what tools to run and how to collect this data. I could just continuously ping google.com all day long but I'm not sure how valuable that data would be. Thoughts?

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• Oracle NoSQL Database: Cleaner Performance

  - by Charles Lamb

  In an earlier post I noted that Berkeley DB Java Edition cleaner performance had improved significantly in release 5.x. From an Oracle NoSQL Database point of view, this is important because Berkeley DB Java Edition is the core storage engine for Oracle NoSQL Database. Many contemporary NoSQL Databases utilize log based (i.e. append-only) storage systems and it is well-understood that these architectures also require a "cleaning" or "compaction" mechanism (effectively a garbage collector) to free up unused space. 10 years ago when we set out to write a new Berkeley DB storage architecture for the BDB Java Edition ("JE") we knew that the corresponding compaction mechanism would take years to perfect. "Cleaning", or GC, is a hard problem to solve and it has taken all of those years of experience, bug fixes, tuning exercises, user deployment, and user feedback to bring it to the mature point it is at today. Reports like Vinoth Chandar's where he observes a 20x improvement validate the maturity of JE's cleaner. Cleaner performance has a direct impact on predictability and throughput in Oracle NoSQL Database. A cleaner that is too aggressive will consume too many resources and negatively affect system throughput. A cleaner that is not aggressive enough will allow the disk storage to become inefficient over time. It has to Work well out of the box, and Needs to be configurable so that customers can tune it for their specific workloads and requirements. The JE Cleaner has been field tested in production for many years managing instances with hundreds of GBs to TBs of data. The maturity of the cleaner and the entire underlying JE storage system is one of the key advantages that Oracle NoSQL Database brings to the table -- we haven't had to reinvent the wheel.

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• central apache log analysis of many hosts

  - by Jason Antman

  We have 30+ apache httpd servers, and are looking to perform analysis on the logs both for historical trending and near "real time" monitoring/alerting. I'm mainly interested in things like error rates (4xx/5xx), response time, overall request rate, etc. but it would also be very useful to pull out more compute-intensive statistics like unique client IPs and user agents per unit of time. I'm leaning towards building this as a centralized collector/server/storage, and am also considering the possibility of storing non-apache logs (i.e. general syslog, firewall logs, etc.) in the same system. Obviously a large part of this will probably have to be custom (at least the connection between pieces and the parsing/analysis we do), but I haven't been able to find much information on people who have done stuff like this, at least at shops smaller than Google/Facebook/etc. who can throw their log data into a hundred-node compute cluster and run Map/Reduce on it. The main things I'm looking for are: - All open source - Some way of collecting logs from apache machines that isn't too resource-intensive, and transports them relatively quickly over the network - Some way of storing them (NoSQL? key-value store?) on the backend, for a given amount of time (and then rolling them up into historical averages) - In the middle of this, a way of graphing in near-real-time (probably also with some statistical analysis on it) and hopefully alerting off of those graphs. Any suggestions/pointers/ideas, to either "products"/projects or descriptions of how other people do this would be greatly helpful. Unfortunately, we're not exactly a new-age-y devops shop, lots of old stuff, homogeneous infrastructure, and strained boxes.

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• Release: Oracle Java Development Kit 8, Update 20

  - by Tori Wieldt

  Java Development Kit 8, Update 20 (JDK 8u20) is now available. This latest release of the Java Platform continues to improve upon the significant advances made in the JDK 8 release with new features, security and performance optimizations. These include: new enterprise-focused administration features available in Oracle Java SE Advanced; products offering greater control of Java version compatibility; security updates; and a very useful new feature, the MSI compatible installer. Download Release Notes Java SE 8 Documentation New tools, features and enhancements highlighted from JDK 8 Update 20 are: Advanced Management Console The Java Advanced Management Console 1.0 (AMC) is available for use with the Oracle Java SE Advanced products. AMC employs the Deployment Rule Set (DRS) security feature, along with other functionality, to give system administrators greater and easier control in managing Java version compatibility and security updates for desktops within their enterprise and for ISVs with Java-based applications and solutions. MSI Enterprise JRE Installer Available for Windows 64 and 32 bit systems in the Oracle Java SE Advanced products, the MSI compatible installer enables system administrators to provide automated, consistent installation of the JRE across all desktops in the enterprise, free of user interaction requirements. Performance: String de-duplication resulting in a reduced footprint Improved support in G1 Garbage Collection for long running apps. A new 'force' feature in DRS (Deployment Rule Set) which allows system administrators to specify the JRE with which an applet or Java Web Start application will run. This is useful for legacy applications so end users don't need to approve security exceptions to run.  Java Mission Control 5.4 with new ease-of-use enhancements and launcher integration with Eclipse 4.4 JavaFX on ARM Nashorn performance improvement by persisting bytecode after inital compilation There's much more information to be found in the JDK 8u20 Release Notes.

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• Are these advanced/unfair interview questions regarding Java concurrency?

  - by sparc_spread

  Here are some questions I've recently asked interviewees who say they know Java concurrency: Explain the hazard of "memory visibility" - the way the JVM can reorder certain operations on variables that are unprotected by a monitor and not declared volatile, such that one thread may not see the changes made by another thread. Usually I ask this one by showing code where this hazard is present (e.g. the NoVisibility example in Listing 3.1 from "Java Concurrency in Practice" by Goetz et al) and asking what is wrong. Explain how volatile affects not just the actual variable declared volatile, but also any changes to variables made by a thread before it changes the volatile variable. Why might you use volatile instead of synchronized? Implement a condition variable with wait() and notifyAll(). Explain why you should use notifyAll(). Explain why the condition variable should be tested with a while loop. My question is - are these appropriate or too advanced to ask someone who says they know Java concurrency? And while we're at it, do you think that someone working in Java concurrency should be expected to have an above-average knowledge of Java garbage collection?

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