Re: [BUGS] BUG #14821: idle_in_transaction_session_timeout sometimes gets ignored when statement timeout is pending

Hi,

As per the bug report at
https://www.postgresql.org/message-id/20170921010956.17345.61461%40wrigleys.postgresql.org
it seems that the query cancellation holdoff logic in ProcessInterrupts is
a bit overly aggressive in keeping other interrupts from running.

In particular I've seen an issue in the wild where
idle_in_transaction_session_timeout did not get triggered because
the HOLD_CANCEL_INTERRUPTS() in SocketBackend wraps around a pq_getbyte()
call, and so ProcessInterrupts doesn't do anything when it gets called
because the query cancel holdoff counter is positive.

Andres suggested the following re-ordering of the logic on -bugs:

> On Wed, Sep 20, 2017 at 6:29 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>
>>
>> if (QueryCancelPending && QueryCancelHoldoffCount != 0)
>> {
>> /* rearm */
>> }
>> else if (QueryCancelPending)
>> {
>> /* handle interrupt */
>> }
>>
>
Which is implemented in the attached patch.

Unless someone wants to pick this up right away, I'll register it in the
next commitfest tomorrow.

Best,
Lukas

--
Lukas Fittl