From: | Thom Brown <thom(at)linux(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Magnus Hagander <magnus(at)hagander(dot)net>, pgsql-docs <pgsql-docs(at)postgresql(dot)org> |
Subject: | Re: track_activity_query_size note |
Date: | 2012-05-24 14:43:43 |
Message-ID: | CAA-aLv6aW9jBHEeBeC4CiMTGOPUNytdiE7d4hv=2FWq=+-rZvQ@mail.gmail.com |
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On 24 May 2012 15:19, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Magnus Hagander <magnus(at)hagander(dot)net> writes:
>> On Thu, May 24, 2012 at 2:59 PM, Thom Brown <thom(at)linux(dot)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
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