Re: Request: pg_cancel_backend variant that handles 'idle in transaction' sessions

JD,

On Wednesday, November 4, 2015, Joshua D. Drake <jd@commandprompt.com> wrote:

On 11/04/2015 02:15 PM, Stephen Frost wrote:

Yeah but anything holding a lock that long can be terminated via
statement_timeout can it not?

Well, no?  statement_timeout is per-statement, while transaction_timeout
is, well, per transaction.  If there's a process which is going and has
an open transaction and it's holding locks, that can be an issue.

No, what I mean is this:

BEGIN;
select * from foo;
update bar;
delete baz;

Each one of those is subject to statement_timeout, yes? If so, then I don't see a point for transaction timeout. You set statement_timeout for what works for your environment. Once the timeout is reached within the statement (within the transaction), the transaction is going to rollback too.

This implies that a statement used takes a long time. It may not. The lock is held at the transaction level not the statement level, which is why a transaction level timeout is actually more useful than a statement level timeout. 

What I'm most interested in, in the use case which I described and which David built a system for, is getting that lock released from the lower priority process to let the higher priority process run. I couldn't care less about statement level anything. 

Thanks!

Stephen