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  • SQL 2000: Intermittent Error 7399 with OLE DB Provider for Microsoft Jet

    - by Tim Lara
    I am using SQL Server 2000 on Windows Server 2003 SP2 and have set up a linked server to point at an Access 97 database using the OLE DB Provider 4.0 for Microsoft Jet. The problem I am having sounds almost exactly like the one described in this Microsoft KB article, except that the error I am getting is intermittent: http://support.microsoft.com/kb/814398 The SQL Server is running under the Local System account (which I don't have authority to change), and the Access 97 .mdb file that the linked server points to is on a Win XP Pro machine on the same LAN as the SQL Server machine, inside of a shared folder with permissions set to "Everyone" and "Full Control". Now, if the linked server connection never worked, it would make more sense that the problem is merely a permissions issue with the Local System account as the KB article above suggests, but the maddening thing is that sometimes the connection works just fine. When it fails, the error message is always the same: Error 7399: OLE DB provider 'Microsoft.Jet.OLEDB.4.0' reported an error. [OLE/DB provider returned message: Unspecified error] OLE DB error trace [OLE/DB Provider 'Microsoft.Jet.OLEDB.4.0' IDBInitialize::Initialize returned 0x80004005: ]. Also, not only does the linked server setup occasionally work just fine on this one particular SQL Server, what is supposed to be exactly the same setup on 25 other servers works just fine EVERY TIME! Obviously, something in the non-working setup must not be exactly the same, but I'm having trouble figuring out where to look for the differences since the error message SQL Server returns is so vague. I know our sysadmins have had numerous issues with Active Directory replication across our domain, so my best guess is that there is some sort of odd group policy corruption going on, but I thought I'd ask here to see if I might be overlooking something more straightforward. Any ideas on how to further isolate the error would be greatly appreciated! For the record, here is a list of things I've already tried: Rebooting the SQL Server machine. Fixes the issue temporarily, then the error returns within a minute or two of startup. (This is why I suspect a rogue group policy that is slow to apply fouling things up.) Importing all database objects from the Access 97 mdb into a new, clean mdb file. Makes no difference. Moving the Access 97 mdb file to a local directory on the SQL Server machine instead of accessing it via a share on the Win XP Pro LAN machine. This works, but does not solve the problem because the mdb needs to be on the client machine for performance reasons and the ability to work "stand alone". Plus, the same shared folder access works fine on all other servers / clients on my network. Compared all the SQL Server, Windows Server, etc versions to a known working setup and everything appears to be the same.

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  • could not bind socket while haproxy restart

    - by shreyas
    I m restarting HAproxy by following command haproxy -f /etc/haproxy/haproxy.cfg -p /var/run/haproxy.pid -sf $(cat /var/run/haproxy.pid) but i get following message [ALERT] 183/225022 (9278) : Starting proxy appli1-rewrite: cannot bind socket [ALERT] 183/225022 (9278) : Starting proxy appli2-insert: cannot bind socket [ALERT] 183/225022 (9278) : Starting proxy appli3-relais: cannot bind socket [ALERT] 183/225022 (9278) : Starting proxy appli4-backup: cannot bind socket [ALERT] 183/225022 (9278) : Starting proxy ssl-relay: cannot bind socket [ALERT] 183/225022 (9278) : Starting proxy appli5-backup: cannot bind socket my haproxy.cfg file looks likefollowing global log 127.0.0.1 local0 log 127.0.0.1 local1 notice #log loghost local0 info maxconn 4096 #chroot /usr/share/haproxy user haproxy group haproxy daemon #debug #quiet defaults log global mode http option httplog option dontlognull retries 3 option redispatch maxconn 2000 contimeout 5000 clitimeout 50000 srvtimeout 50000 listen appli1-rewrite 0.0.0.0:10001 cookie SERVERID rewrite balance roundrobin server app1_1 192.168.34.23:8080 cookie app1inst1 check inter 2000 rise 2 fall 5 server app1_2 192.168.34.32:8080 cookie app1inst2 check inter 2000 rise 2 fall 5 server app1_3 192.168.34.27:8080 cookie app1inst3 check inter 2000 rise 2 fall 5 server app1_4 192.168.34.42:8080 cookie app1inst4 check inter 2000 rise 2 fall 5 listen appli2-insert 0.0.0.0:10002 option httpchk balance roundrobin cookie SERVERID insert indirect nocache server inst1 192.168.114.56:80 cookie server01 check inter 2000 fall 3 server inst2 192.168.114.56:81 cookie server02 check inter 2000 fall 3 capture cookie vgnvisitor= len 32 option httpclose # disable keep-alive rspidel ^Set-cookie:\ IP= # do not let this cookie tell our internal IP address listen appli3-relais 0.0.0.0:10003 dispatch 192.168.135.17:80 listen appli4-backup 0.0.0.0:10004 option httpchk /index.html option persist balance roundrobin server inst1 192.168.114.56:80 check inter 2000 fall 3 server inst2 192.168.114.56:81 check inter 2000 fall 3 backup listen ssl-relay 0.0.0.0:8443 option ssl-hello-chk balance source server inst1 192.168.110.56:443 check inter 2000 fall 3 server inst2 192.168.110.57:443 check inter 2000 fall 3 server back1 192.168.120.58:443 backup listen appli5-backup 0.0.0.0:10005 option httpchk * balance roundrobin cookie SERVERID insert indirect nocache server inst1 192.168.114.56:80 cookie server01 check inter 2000 fall 3 server inst2 192.168.114.56:81 cookie server02 check inter 2000 fall 3 server inst3 192.168.114.57:80 backup check inter 2000 fall 3 capture cookie ASPSESSION len 32 srvtimeout 20000 option httpclose # disable keep-alive option checkcache # block response if set-cookie & cacheable rspidel ^Set-cookie:\ IP= # do not let this cookie tell our internal IP address #errorloc 502 http://192.168.114.58/error502.html #errorfile 503 /etc/haproxy/errors/503.http errorfile 400 /etc/haproxy/errors/400.http errorfile 403 /etc/haproxy/errors/403.http errorfile 408 /etc/haproxy/errors/408.http errorfile 500 /etc/haproxy/errors/500.http errorfile 502 /etc/haproxy/errors/502.http errorfile 503 /etc/haproxy/errors/503.http errorfile 504 /etc/haproxy/errors/504.http what is wrong with my aproach

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  • Linux : Forward users mail using exim4 server (newbiw warning)

    - by llazzaro
    Hello, I have a network of linux server, one of them is running exim4 that server could send [email protected]. At exim4 server, I had setup an alias for the users accounts ...for example root : [email protected] But I have other server, if I put the alias email is marked as spam...since they arent using exim4 server. I want to configure the other server to use that exim4 server, in order to dont get the mails mark as spam. Well I know this is really newbie question, but searching at google is difficult since it confuses exim4 server configuration than the client configuration to use exim4 server. Remember, I want root@server1,root@server2,etc mails send via exim4 server!

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  • Server Core remote management from Windows 7 machine

    - by Robert Koritnik
    I've installed Remote Server Administration Tools for Windows 7 because I would like to administer my Windows Server 2008 R2 Server Core machine. The problem that I'm getting when I try to run Server Manager is: Connecting to remote server failed with the following error message: Access is denied. For more information, see the about_Remote_Troubleshooting Help topic. This is what I've done so far: I'm running WinRM service on both machines (Server and Window 7) I've added my server to trusted hosts on my Windows 7 machine: winrm set winrm/config/client @{TrustedHosts="WINSRV2"} I've added registry entry on Windows 7 machine: reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System /v LocalAccountTokenFilterPolicy /t REG_DWORD /d 1 /f I've enabled Remote Management inbound rule on server firewall using CoreConfigurator 2.0 both machines are in the same subnet and when I search for network machines on Windows 7 I see my server. Question What else should I do to make it work? I would like to run several different remote management tools against my server machine.

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  • Make Apache Ignore Domains on the Same Server (Ubuntu 9.10). How?

    - by vladikoff
    Hello, I'm running Apache on Ubuntu 9.10. I want Apache to ignore certain domains on my server, and let other HTTP servers make full use of them. I've used mod_proxy and other Apache modules to configure the proxy/redirect to certain ports but sometimes that's too much work or doesn't work properly. Example: Server 00.00.000.000 domain1.com:80 - Apache domain2.com:80 - Apache domain3.com:80 - Webrick domain4.com:80 - Jetty Is this possible?

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  • OSX Server 3, Mac clients binding to OD and Profile Manager failing

    - by dbf
    I've made a setup containing a Mac Mini with OSX Server 3 (Mavericks 10.9.2) using Open Directory and Profile Manager (Mail, etc all set up and working). Now the thing is, internally on the local network, everything works great. Clients can bind to the OD and the users are able to login. I can install trust and settings profiles (either custom or group profiles) and all services in the profiles mentioned are being configured correctly. I can log in and out, hump around and do it a 100 times on different macs with different users, it works. My goal is to make this service publicly. The domain is with a FQDN which I own, for simplicity let's say server.domain.com. Now the only way for me to bind the clients to the OD is using LDAP mapping RCF2307 (without SSL) and a DN suffix of dc=server,dc=domain,dc=com using the Directory Utility. The options from server, or open directory will throw several errors like Connection failed to node '/LDAPv3/server.domain.com (2100). First of all I don't really understand the problem why clients can't bind to the OD like it does locally, with and without SSL (all ports are open, literally all ports are open, not just 389,636 and 1640, wasn't sure if I was missing any). When the clients are using LDAP mapping RFC2307 to bind (without SSL only), clients are able to authenticate, login and even load the Trust profile. But every Settings profile will fail with a Debug Message: Unable to find GUID in user record OD or fail to install saying missing user identification. Is there any way to get this to work without RFC2307? Because there is quite some stuff missing when using RFC2307 and not pull the mapping from the server or use open directory. Is this setup even possible? Or should I use VPN to authenticate with the OD? The network setup is a Modem/Router (DHCP off) with WAN NATted to an Airport Extreme (Using DHCP+NAT). The AE does notify with a double NAT message but I haven't had any problems with it on any other service. So WAN - 192.168.2.220 (static), AE - 10.0.1.* (dhcp) Output of DIG from the outside using dig server.domain.com ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;server.domain.com. IN A ;; ANSWER SECTION: server.domain.com. 77 IN A 91.50.*.* (valid WAN IP) ;; SERVER 172.*.*.1#53(172.*.*.1) (iPhone) DIG locally from a client and server (same output) ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;server.domain.com. IN A ;; ANSWER SECTION: server.domain.com. 10800 IN A 10.0.1.11 ;; AUTHORITY SECTION: server.domain.com. 10800 IN NS domain.com. (used for email send in relay) server.domain.com. 10800 IN NS server.domain.com. ;; SERVER 10.0.1.11#53(10.0.1.11) Are there any things I should check? Only have OSX. -- double NAT issue, plugged in the server directly on the Modem/Router with a static IP and issue remains. Guess that rules out the double NAT thing. -- changeip -checkhostname comes with There is nothing to change, e.g. success. Primary address = 10.0.1.11 Current HostName = server.domain.com DNS HostName = server.domain.com For now, I've made a workaround by using an admin account that forces a permanent VPN connection on boot. That means before it comes to the login, a connection is already made or underway. I will continue this post when I have more time, also locating all the necessary .log files of each application involved. I have some suspicions but have to debug a bit more when I have more time on my hands .. Unless, of course, I get sidetracked with having a life. Which is arguably not very likely. krypted.com

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  • Install Sql Server Developer Edition 32-bit (or Enterprise Edition) on Windows 7 Home Premium 64-bit

    - by ali62b
    Is there any work around to Successfully install SQL server 2008 32-bit on Windows 7 Home premium 64-bit ? If this is the case I first installed VS 2008 SP 1 on my machine and when I click on install.exe file for installing SQL Server 2008 (Developer Edition) I get an error related to .NET Framework version which is installed already on my PC. { I get the same error trying to install Enterprise Edition}

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  • Remote Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (104)

    - by user39891
    Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for multiplexing connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on their port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR?), which in the network context suggests that ...'the connection was reset by peer'; or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? I use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right, but of course in series not parallel. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. Any ideas? I cannot figure-out whatever is wrong even with Valgrind, GDB or much logging. Kindly help where you can.

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  • How are SQL Server CALs counted?

    - by Sam
    Running a SQL Server, as far as I understand it, you need one CAL for every user who connects to the database server. But what happens if the only computer which is accessing the SQL Server is the server running your business layer? If, for example, you got 1 SQL Server and 1 Business logic server, and 100 Clients who all just query and use the business logic server. No client is using the SQL Server directly, no one is even allowed to contact it. So, since there is only one computer using the SQL server, do I need only 1 CAL??? I somehow can't believe this would count as only 1 CAL needed for the SQL Server, but I would like to know why not.

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  • Best way to backup a SQL Server database nightly?

    - by Urda
    What is the best way to backup a SQL Server 2005 database nightly? I'm looking for a solution/strategy that would make the database backup file, and place it in an "outgoing" directory. We're wanting our FTP software to move it out to an offsite server. Any suggestions on how to make this work as desired?

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  • Is it possible to dedicate the physical screen of a vmware server machine to a guest vm graphically?

    - by matnagel
    I have a vmware server 2.x running on ubuntu server (8.04). So the graphics card and the screen of the physical box are unused (I log in remotely and the host os has only the cli console installed). I wonder if it is possible to assign this graphics card to a virtual machine directly and use it for the gui of this guest? Or maybe if I add a second graphics card to the machine?

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  • How to share drive space from vmware server 2 host to a guest?

    - by matnagel
    In the vmware tools in the guest there is an option to access shares from the host. What is the way to create such shares on a vmware 2 host? I did not find where in infrastructure web access. I also went through the vmware server 2 user's guide but did not see it mentioned. Can you help? This is an ubuntu 64 bit server 8.04 LTS host.

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  • Is this distributed database server idea feasible?

    - by David
    I often use SQLite for creating simple programs in companies. The database is placed on a file server. This works fine as long as there are not more than about 50 users working towards the database concurrently (though depending on whether it is reads or writes). Once there are more than this, they will notice a slowdown if there are a lot of concurrent writing on the server as lots of time is spent on locks, and there is nothing like a cache as there is no database server. The advantage of not needing a database server is that the time to set up something like a company Wiki or similar can be reduced from several months to just days. It often takes several months because some IT-department needs to order the server and it needs to conform with the company policies and security rules and it needs to be placed on the outsourced server hosting facility, which screws up and places it in the wrong localtion etc. etc. Therefore, I thought of an idea to create a distributed database server. The process would be as follows: A user on a company computer edits something on a Wiki page (which uses this database as its backend), to do this he reads a file on the local harddisk stating the ip-address of the last desktop computer to be a database server. He then tries to contact this computer directly via TCP/IP. If it does not answer, then he will read a file on the file server stating the ip-address of the last desktop computer to be a database server. If this server does not answer either, his own desktop computer will become the database server and register its ip-address in the same file. The SQL update statement can then be executed, and other desktop computers can connect to his directly. The point with this architecture is that, the higher load, the better it will function, as each desktop computer will always know the ip-address of the database server. Also, using this setup, I believe that a database placed on a fileserver could serve hundreds of desktop computers instead of the current 50 or so. I also do not believe that the load on the single desktop computer, which has become database server will ever be noticable, as there will be no hard disk operations on this desktop, only on the file server. Is this idea feasible? Does it already exist? What kind of database could support such an architecture?

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  • SQL server environment

    - by Olegas D
    Hello I'm considering a bit of changes in current sales environment. And trying to check all cons and pros. Current situation. SQL server (quite decent HP server - server1) + backup server (smaller Dell server - server2). all sql files and sql server itself are on the server1. If something goes wrong with server1 I will have to manually move to server2. Connecting to the sql server: 1 HQ (where server located) + 4 sites through VPN. Now I'm considering 2 scenarios: Buy some storage system + update existing servers (add ram, upgrade processors) and go for VMWare ESXI. Rent a server at a datacenter + rent virtual server in case real server goes down. Also rent some space at data storage to keep SQL files there. Have anyone considered these things and maybe found some good pros/cons list? ;) Thanks

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  • SQL Server Express with Advanced Services (with Reporting Services)???

    - by Fretwizard
    I have tried to download SQL Server 2005 Express edition about 4 times trying to find the correct version that has business intelligence studio and reporting services in it? Every time I try to unhide the advanced configuration during install, it's never there... Can anyone point me to the correct download? Looking for 2005 (not 2008) because my work SQL server that I am trying to learn this for is 2005, and the training material I have is for 2005 and VS 2008 does not want to integrate with SQL2008 express.

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  • Is it possible to put an 8000 series socket-F Opteron into a dual-socket motherboard?

    - by René Kåbis
    Exactly what it says on the Tin. I have a dual-socket, socket-F motherboard in which I am looking to put two high-end quad-core Opterons, but the 2000 series are nearly double the price of the 8000 series on eBay. Can I just drop in a pair of 8000 series processors and be done with it, or are there processor-critical motherboard features that would be present on a quad(+)-socket motherboard that don’t exist on a dual-socket motherboard? Please elaborate or link to resources that can explain this further, as I am not adverse to research (and I am interested in the technical issues involved) I am probably using the wrong search terms, as Google failed to return anything within the first few dozen results.

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  • SQL SERVER – Concurrency Basics – Guest Post by Vinod Kumar

    - by pinaldave
    This guest post is by Vinod Kumar. Vinod Kumar has worked with SQL Server extensively since joining the industry over a decade ago. Working on various versions from SQL Server 7.0, Oracle 7.3 and other database technologies – he now works with the Microsoft Technology Center (MTC) as a Technology Architect. Let us read the blog post in Vinod’s own voice. Learning is always fun when it comes to SQL Server and learning the basics again can be more fun. I did write about Transaction Logs and recovery over my blogs and the concept of simplifying the basics is a challenge. In the real world we always see checks and queues for a process – say railway reservation, banks, customer supports etc there is a process of line and queue to facilitate everyone. Shorter the queue higher is the efficiency of system (a.k.a higher is the concurrency). Every database does implement this using checks like locking, blocking mechanisms and they implement the standards in a way to facilitate higher concurrency. In this post, let us talk about the topic of Concurrency and what are the various aspects that one needs to know about concurrency inside SQL Server. Let us learn the concepts as one-liners: Concurrency can be defined as the ability of multiple processes to access or change shared data at the same time. The greater the number of concurrent user processes that can be active without interfering with each other, the greater the concurrency of the database system. Concurrency is reduced when a process that is changing data prevents other processes from reading that data or when a process that is reading data prevents other processes from changing that data. Concurrency is also affected when multiple processes are attempting to change the same data simultaneously. Two approaches to managing concurrent data access: Optimistic Concurrency Model Pessimistic Concurrency Model Concurrency Models Pessimistic Concurrency Default behavior: acquire locks to block access to data that another process is using. Assumes that enough data modification operations are in the system that any given read operation is likely affected by a data modification made by another user (assumes conflicts will occur). Avoids conflicts by acquiring a lock on data being read so no other processes can modify that data. Also acquires locks on data being modified so no other processes can access the data for either reading or modifying. Readers block writer, writers block readers and writers. Optimistic Concurrency Assumes that there are sufficiently few conflicting data modification operations in the system that any single transaction is unlikely to modify data that another transaction is modifying. Default behavior of optimistic concurrency is to use row versioning to allow data readers to see the state of the data before the modification occurs. Older versions of the data are saved so a process reading data can see the data as it was when the process started reading and not affected by any changes being made to that data. Processes modifying the data is unaffected by processes reading the data because the reader is accessing a saved version of the data rows. Readers do not block writers and writers do not block readers, but, writers can and will block writers. Transaction Processing A transaction is the basic unit of work in SQL Server. Transaction consists of SQL commands that read and update the database but the update is not considered final until a COMMIT command is issued (at least for an explicit transaction: marked with a BEGIN TRAN and the end is marked by a COMMIT TRAN or ROLLBACK TRAN). Transactions must exhibit all the ACID properties of a transaction. ACID Properties Transaction processing must guarantee the consistency and recoverability of SQL Server databases. Ensures all transactions are performed as a single unit of work regardless of hardware or system failure. A – Atomicity C – Consistency I – Isolation D- Durability Atomicity: Each transaction is treated as all or nothing – it either commits or aborts. Consistency: ensures that a transaction won’t allow the system to arrive at an incorrect logical state – the data must always be logically correct.  Consistency is honored even in the event of a system failure. Isolation: separates concurrent transactions from the updates of other incomplete transactions. SQL Server accomplishes isolation among transactions by locking data or creating row versions. Durability: After a transaction commits, the durability property ensures that the effects of the transaction persist even if a system failure occurs. If a system failure occurs while a transaction is in progress, the transaction is completely undone, leaving no partial effects on data. Transaction Dependencies In addition to supporting all four ACID properties, a transaction might exhibit few other behaviors (known as dependency problems or consistency problems). Lost Updates: Occur when two processes read the same data and both manipulate the data, changing its value and then both try to update the original data to the new value. The second process might overwrite the first update completely. Dirty Reads: Occurs when a process reads uncommitted data. If one process has changed data but not yet committed the change, another process reading the data will read it in an inconsistent state. Non-repeatable Reads: A read is non-repeatable if a process might get different values when reading the same data in two reads within the same transaction. This can happen when another process changes the data in between the reads that the first process is doing. Phantoms: Occurs when membership in a set changes. It occurs if two SELECT operations using the same predicate in the same transaction return a different number of rows. Isolation Levels SQL Server supports 5 isolation levels that control the behavior of read operations. Read Uncommitted All behaviors except for lost updates are possible. Implemented by allowing the read operations to not take any locks, and because of this, it won’t be blocked by conflicting locks acquired by other processes. The process can read data that another process has modified but not yet committed. When using the read uncommitted isolation level and scanning an entire table, SQL Server can decide to do an allocation order scan (in page-number order) instead of a logical order scan (following page pointers). If another process doing concurrent operations changes data and move rows to a new location in the table, the allocation order scan can end up reading the same row twice. Also can happen if you have read a row before it is updated and then an update moves the row to a higher page number than your scan encounters later. Performing an allocation order scan under Read Uncommitted can cause you to miss a row completely – can happen when a row on a high page number that hasn’t been read yet is updated and moved to a lower page number that has already been read. Read Committed Two varieties of read committed isolation: optimistic and pessimistic (default). Ensures that a read never reads data that another application hasn’t committed. If another transaction is updating data and has exclusive locks on data, your transaction will have to wait for the locks to be released. Your transaction must put share locks on data that are visited, which means that data might be unavailable for others to use. A share lock doesn’t prevent others from reading but prevents them from updating. Read committed (snapshot) ensures that an operation never reads uncommitted data, but not by forcing other processes to wait. SQL Server generates a version of the changed row with its previous committed values. Data being changed is still locked but other processes can see the previous versions of the data as it was before the update operation began. Repeatable Read This is a Pessimistic isolation level. Ensures that if a transaction revisits data or a query is reissued the data doesn’t change. That is, issuing the same query twice within a transaction cannot pickup any changes to data values made by another user’s transaction because no changes can be made by other transactions. However, this does allow phantom rows to appear. Preventing non-repeatable read is a desirable safeguard but cost is that all shared locks in a transaction must be held until the completion of the transaction. Snapshot Snapshot Isolation (SI) is an optimistic isolation level. Allows for processes to read older versions of committed data if the current version is locked. Difference between snapshot and read committed has to do with how old the older versions have to be. It’s possible to have two transactions executing simultaneously that give us a result that is not possible in any serial execution. Serializable This is the strongest of the pessimistic isolation level. Adds to repeatable read isolation level by ensuring that if a query is reissued rows were not added in the interim, i.e, phantoms do not appear. Preventing phantoms is another desirable safeguard, but cost of this extra safeguard is similar to that of repeatable read – all shared locks in a transaction must be held until the transaction completes. In addition serializable isolation level requires that you lock data that has been read but also data that doesn’t exist. Ex: if a SELECT returned no rows, you want it to return no. rows when the query is reissued. This is implemented in SQL Server by a special kind of lock called the key-range lock. Key-range locks require that there be an index on the column that defines the range of values. If there is no index on the column, serializable isolation requires a table lock. Gets its name from the fact that running multiple serializable transactions at the same time is equivalent of running them one at a time. Now that we understand the basics of what concurrency is, the subsequent blog posts will try to bring out the basics around locking, blocking, deadlocks because they are the fundamental blocks that make concurrency possible. Now if you are with me – let us continue learning for SQL Server Locking Basics. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Concurrency

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  • Are parallel calls to send/recv on the same socket valid?

    - by Jay
    Can we call send from one thread and recv from another on the same socket? Can we call multiple sends parallely from different threads on the same socket? I know that a good design should avoid this, but I am not clear how these system APIs will behave. I am unable to find a good documentation also for the same. Any pointers in the direction will be helpful.

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