Can jdbc connections which are closed due to database un-availability be recovered.
To give back ground I get following errors in sequence. It doesn't look to be manual re-start. The reason for my question is that I am told that the app behaved correctly without
the re-start. So if the connection was lost, can it be recovered, after a DB re-start.
java.sql.SQLException: ORA-12537: TNS:connection closed
java.sql.SQLRecoverableException: ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
IBM AIX RISC System/6000 Error: 2: No such file or directory
java.sql.SQLRecoverableException: ORA-01033: ORACLE initialization or shutdown in progress
No. The connection is "dead". Create a new connection.
A good approach is to use a connection pool, which will test if the connection is still OK before giving it to you, and automatically create a new connection if needed.
There are several open source connection pools to use. I've used Apache's JDCP, and it worked for me.
Edited:
Given that you want to wait until the database comes back up if it's down (interesting idea), you could implement a custom version of getConnection() that "waits a while and tries again" if the database doesn't respond.
p.s. I like this idea!
The connection cannot be recovered. What can be done is to failover the connection to another database instance. RAC and data guard installations support this configuration.
This is no problem for read-only transactions. However for transactions that execute DML this can be a problem, especially if the last call to the DB was a commit. In case of a commit the client cannot tell if the commit call completed or not. When did the DB fail; before executing the commit, or after executing the commit (but not sending back the acknowledgment to the client). Only the application has this logic and can do the right thing. If the application after failing over does not verify the state of the last transaction, duplicate transactions are possible. This is a known problem and most of us experienced it buying tickets or similar web transactions.
Related
In our production environment there are sometimes peaks of ORA-12599 errors the connection works otherwise.
The description is not quite clear to me.
Cause: The data received is not the same as the data sent.
Action:
Attempt the transaction again. If error persists, check (and correct)
the integrity of your physical connection.
https://www.oraexcel.com/database-oracle-11gR2-ORA-12599
Does that mean there is a problem with my network cable? Or any other Hardware?
Because our DBA said the error can be caused by a configuration issue on the client side.
Edit:
It started without any changes on the client or server side. And there are spikes. 80 errors in an hour and then no errors for 4 hours while the load is more or less constant
It can mean a mismatch in how the client and the server are wishing to communicate (in encrypted fashion). For example, trying to connect to an 11g database with 10g JDBC drivers will get this because the encryption implementation changed between these versions.
Check your local (ie, client) sqlnet.ora file - you may need to opt for a different method or change the order of them.
The error can be typically be ignored (its informational) but using the latest drivers will normally resolve the issue.
We had sporadic ORA-12599 errors and also ORA-24300 ("bad value for mode") in a Python web app using Flask and uwsgi. It turned out to be caused by multiple worker processes writing and reading to/from the same TCP connection to the DB, giving chaotic communications on the socket.
In our setup this was caused by creating the TCP connections to the DB before uwsgi forked the workers, and the file descriptors being inherited. We fixed this by using uwgsi's lazy-apps mode.
See also this question.
What does it do? How does it work? Why am I supposed to test the database connection before "borrowing it from the pool"?
I was not able to find any related information as to why I should be using it. Just how to use it. And it baffles me.
Can anyone provide some meaningful definition and possibly resources to find out more?
"test-on-borrow" indicates that a connection from the pool has to be validated usually by a simple SQL validation query defined in "validationQuery". These two properties are commonly used in conjunction to make sure that the current connections in the pool are not stale (no longer connected to the DB actively as a result of a DB restart, or timeouts enforced by the DB, or whatever other reason that might cause stale connections). By testing the connections on borrow, the application can automatically reconnect to the DB using new connections (and dropping the invalid ones) without a manual restart of the app and thus preventing DB connection errors in the app.
You can find more information on jdbc connection pool attributes here:
https://tomcat.apache.org/tomcat-8.0-doc/jdbc-pool.html#Common_Attributes
My application executes many queries and it is sure that all connections are closed well. PgAdmin shows many queries have gone "Idle in transaction" and finally DB becomes unresponsive. Is there a way to get the query caused to be 'Idle in transaction' ? Or any other tool which can track it ? Postgres 8.1 is used.
Edit: Connection Pool is used. Also, the state ' in transaction' got cleared after couple of minutes. Then, if any connection is opened, how this get cleared ?
If you check information in Postgres documentation regarding this:
idle in transaction (waiting for client inside a BEGIN block), or a
command type name such as SELECT. Also, waiting is attached if the
server process is presently waiting on a lock held by another server
process
I would suggest following things:
enable logging of "long queries" using log_min_duration_statement
and log_lock_waits option in postgresql.conf in Error Reporting and Logging section
check Lock Management parameters of postgresql.conf configuration file,deadlock_timeout option in particular
check Lock Monitoring article on Postgres Wiki and pg_locks view in Postgres
This is clean signal, so some about closing transaction and closing sessions is wrong in your application. The queries works well. Check your application - unexpected exceptions, fails, ... Some applications are pretty buggy - usually it is pretty serious problem. Orphaned transactions block VACUUM and block reusing connections.
I have 3 servers set up for SQL mirroring and automatic failover using a witness server. This works as expected.
Now my application that connects to the database, seems to have a problem when a failover occurs - I need to manually intervene and change connection strings for it to connect again.
The best solution I've found so far involves using Failover Partner parameter of the connection string, however it's neither intuitive nor complete: Data Source="Mirror";Failover Partner="Principal" found here.
From the example in the blog above (scenario #3) when the first failover occurs, and principal (failover partner) is unavailable, data source is used instead (which is the new principal). If it fails again (and I only tried within a limited period), it then comes up with an error message. This happens because the connection string is cached, so until this is refreshed, it will keep coming out with an error (it seems connection string refreshes ~5 mins after it encounters an error). If after failover I swap data source and failover partner, I will have one more silent failover again.
Is there a way to achieve fully automatic failover for applications that use mirroring databases too (without ever seeing the error)?
I can see potential workarounds using custom scripts that would poll currently active database node name and adjust connection string accordingly, however it seems like an overkill at the moment.
Read the blog post here
http://blogs.msdn.com/b/spike/archive/2010/12/15/running-a-database-mirror-setup-with-the-sqlbrowser-service-off-may-produce-unexpected-results.aspx
It explains what is happening, the failover partner is actually being read from the sql server not from your config. Run the query in that post to find out what is actually being used as the failover server. It will probably be a machine name that is not discoverable from where your client is running.
You can clear the application pool in the case a failover has happened. Not very nice I know ;-)
// ClearAllPools resets (or empties) the connection pool.
// If there are connections in use at the time of the call,
// they are marked appropriately and will be discarded
// (instead of being returned to the pool) when Close is called on them.
System.Data.SqlClient.SqlConnection.ClearAllPools();
We use it when we change an underlying server via SQL Server alias, to enforce a "refresh" of the server name.
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.clearallpools.aspx
The solution is to turn connection pooling off Pooling="false"
Whilst this has minimal impact on small applications, I haven't tested it with applications that receive hundreds of requests per minute (or more) and not sure what the implications are. Anyone care to comment?
Try this connectionString:
connectionString="Data Source=[MSSQLPrincipalServerIP,MSSQLPORT];Failover Partner=[MSSQLMirrorServerIP,MSSQLPORT];Initial Catalog=DatabaseName;Persist Security Info=True;User Id=userName; Password=userPassword.; Connection Timeout=15;"
If you are using .net development, you can try to use ObjAdoDBLib or PigSQLSrvLib and PigSQLSrvCoreLib, and the code will become simple.
Example code:
New object
ObjAdoDBLib
Me.ConnSQLSrv = New ConnSQLSrv(Me.DBSrv, Me.MirrDBSrv, Me.CurrDB, Me.DBUser, Me.DBPwd, Me.ProviderSQLSrv)
PigSQLSrvLib or PigSQLSrvCoreLib
Me.ConnSQLSrv = New ConnSQLSrv(Me.DBSrv, Me.MirrDBSrv, Me.CurrDB, Me.DBUser, Me.DBPwd)
Execute this method to automatically connect to the online database after the mirror database fails over.
Me.ConnSQLSrv.OpenOrKeepActive
For more information, see the relevant links.
https://www.nuget.org/packages/ObjAdoDBLib/
https://www.nuget.org/packages/PigSQLSrvLib/
https://www.nuget.org/packages/PigSQLSrvCoreLib/
I have a client-server app that uses .NET SqlClient Data Provider to connect to sql server - pretty standard stuff. By default how long must connections be idle before the connection pooling manager will close the database connection and remove it from the pool? What setting if any controls this?
This MSDN document only says
The connection pooler removes a connection from the pool after it has been idle for a long time, or if the pooler detects that the connection with the server has been severed.
A few years ago the answer beneath was the situation, but now it's changed so you can refer to the source and write up a summary :)
Old answer
This excellent article tells us what we need to know, using reflection to reveal the inner workings of connection pooling.
From how I understand it, 'closed' connections are cleaned up periodically on a semi-random interval. The cleanup process runs somewhere between every 2min and 3min 50s, but it needs to run twice before a 'closed' connection will be properly closed. Therefore after 7min 40s of being 'closed' the underlying sql connection should be properly closed, but it could be as short as 2min. At the time of writing the first connection pool created in a process would always have a timer interval of 3min 10s, so you'd normally see sql connections being closed somewhere between 3min 10s and 6min 20s after you call Close() on the ADO object.
Obviously this uses undocumented code so could change in future - or could even have changed since that article was written.
Please go through this:
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.connectionstring%28VS.80%29.aspx
The part
"The following table lists the valid
names for connection pooling values
within the ConnectionString."
seems to be of your interest.