Improvements for statement cancellation

Hi.

I have a nasty issue which involves WebLogic, pgpool-II and Postgres JDBC.

WebLogic has a habit on calling Statement.cancel() on all cached (by
itself) statements, when closing it's connection pools. It also calls
Statement.cancel() in some other circumstances, as far as I can understand,
and example is an abnormal transaction rollback.

Postgres JDBC, on Statement.cancel(), unconditionally calls
Connection.cancelQuery().

pgpool-II has a special code that sleeps for one second before releasing
cancel request (rather, between sending cancel requests to all backends
involved in a connection). It has its reasons for doing that sleep.

This leaves me with a neraly-locked up system sometimes, as the
cancellation process can take a very long time (these seconds do add up).
Below is a sample stack trace of how it looks like, code path-wise.

I'm wondering if it's possible if Postgres JDBC could change the
implementation of cancel() so that cancelQuery() is only sent if the
statement being called is the actual statement that is being executed on
the connection, and otherwise be a no-op.

at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at
org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:143)
at
org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:112)
at
org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:71)
at org.postgresql.core.PGStream.ReceiveEOF(PGStream.java:530)
at
org.postgresql.core.v3.ProtocolConnectionImpl.sendQueryCancel(ProtocolConnectionImpl.java:98)
at
org.postgresql.jdbc2.AbstractJdbc2Connection.cancelQuery(AbstractJdbc2Connection.java:1023)
at
org.postgresql.jdbc2.AbstractJdbc2Statement.cancel(AbstractJdbc2Statement.java:2775)
at sun.reflect.GeneratedMethodAccessor123.invoke(Unknown Source)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at
org.postgresql.ds.jdbc23.AbstractJdbc23PooledConnection$StatementHandler.invoke(AbstractJdbc23PooledConnection.java:453)
at $Proxy50.cancel(Unknown Source)
at
weblogic.jdbc.common.internal.ConnectionEnv.cancelStatements(ConnectionEnv.java:703)