Re: Connection terminated by the server causes deadlock in jdbc client side connection

Hi,

We are experiencing very frequent deadlocks in pgsql jdbc connections. The scenario is a replicated database with hot_standby = on

At times of high volumes of queries in both the primary and the replicated server, we sometimes get the following log indicating that the server has terminated the connection in the replicated database.

FATAL:  terminating connection due to conflict with recovery

DETAIL:  User query might have needed to see row versions that must be removed.

HINT:  In a moment you should be able to reconnect to the database and repeat your command.

This is expected and we see no issue with that. What I did not expect, however, is that in the JDBC client side, the connection is deadlocked.

java.lang.Thread.State: RUNNABLE

at java.net.SocketOutputStream.socketWrite0(Native Method)

at java.net.SocketOutputStream.socketWrite(Unknown Source)

at java.net.SocketOutputStream.write(Unknown Source)

at java.io.BufferedOutputStream.flushBuffer(Unknown Source)

at java.io.BufferedOutputStream.flush(Unknown Source)

- locked <0x0000000700742e30> (a java.io.BufferedOutputStream)

at org.postgresql.core.PGStream.flush(PGStream.java:518)

at org.postgresql.core.v3.ProtocolConnectionImpl.close(ProtocolConnectionImpl.java:136)

at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:280)

- locked <0x0000000700742fd0> (a org.postgresql.core.v3.QueryExecutorImpl)

at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:547)

at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:417)

at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:302)

...

Looking at the Postgres JDBC code, I notice that ProtocolConnectionImpl.close() (invoked by the exception handler in QueryExecutorImpl.execute) is trying to 'gracefully close' by sending an 'X' to the server before actually closing the socket.

...

if (logger.logDebug()) logger.debug(" FE=> Terminate"); pgStream.SendChar('X'); pgStream.flush(); pgStream.close(); ...

Does this make sense in a scenario of a connection which has already been terminated by the server side? 

At times of high load, all connections in the pool get eventually locked with exactly the same stack trace. 

I'd appreciate any advice on how to handle this. Could this be a bug in the JDBC driver?

Thanks,

Leonardo