Re: Re: sudden spurt in swap utilization (was:cpu bound postgresql setup.)

On 25/06/10 20:00, Rajesh Kumar Mallah wrote:
> Dear tom, we have autocommit off in dbi. Any commit or rollback from
> the persistent modperl process immediately issues begin work; if the
> modperl process is waiting for request the database backend remains in
> idle in transaction state. Unless we modify data in a http request we
> neighter issue a commit nor rollback.
>

The backend shouldn't go to 'idle in transaction' state until there is
some activity within the transaction. I've attached an example script to
demonstrate this - note that even SELECT queries will leave the handle
as 'IDLE in transaction' unless you've changed the transaction isolation
level from the default.

Any queries that are idle in transaction will block connection pooling
and cause old versions of table rows to hang around, as described in
other replies. Note that this is nothing to do with mod_perl, it's
purely due to the way transactions are handled - a one-off script would
also have this issue, but on exit issues an implicit rollback and
disconnects.

Typically your database wrapper would handle this (I think DBIx::Class
should take care of this automatically, although I haven't used it myself).

Tom