Re: track_activity_query_size note

On 24 May 2012 15:19, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Magnus Hagander <magnus@hagander.net> writes:
>> On Thu, May 24, 2012 at 2:59 PM, Thom Brown <thom@linux.com> wrote:
>>>> I attach a proposed change to the docs which points out that if the
>>>> size of track_activity_query_size is changed and the is server
>>>> restarted, it won't have any effect if query statistics are already
>>>> present.
>
>> Ah, suddenly it makes sense.
>
>> And in that case yes, the docs changes should go under
>> pg_stat_statements, I believe.
>
> But surely the statement is flat out wrong; or if it's not wrong,
> there's a bug somewhere.  We do not absorb the value of
> track_activity_query_size from the stats file.

Hmm... well I think I may have misinterpreted the behaviour.  What I
saw was the size of the query shown in pg_stat_statements remaining
unchanged after restarting the server with a new
track_activity_query_size value, but I'm guessing this is merely
because its representation remains unchanged.  If I run the same query
with an extra condition on the end, it shows up as a separate row, but
not truncated to the same length as the previous query.

So I retract my proposed amendment as it's a falsehood.  It was merely
an unexpected behaviour on my part.  The truth is that pre-existing
queries listed in pg_stat_statements won't magically become less
truncated if track_activity_query_size is increased.  That only
applies to new entries from that point that don't share the same query
signature.

--
Thom