From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Adrien Nayrat <adrien.nayrat@anayrat.info>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: idea: log_statement_sample_rate - bottom limit for sampling
Date: Sun, 4 Aug 2019 23:41:54 +0200
Message-ID: <20190804214154.tbr5pbg5wss2adfu@development> (raw)
In-Reply-To: <20190804204848.7f7ypsbijpgxojxx@development>
References: <20190727221948.irg6sfqh57dynoc7@development>
<4540bafe-1b23-a6ce-a313-f3b03bb418df@anayrat.info>
<cfe72bab-dc4c-d194-4ea2-ac9dc89d6243@anayrat.info>
<20190801100445.yo5v3pdxelijztzm@development>
<3f6b75ea-03bb-7c35-1f20-e989f4b7f9ac@anayrat.info>
<20190804191037.em6rmlvxjpcsjtqu@development>
<25079.1564946172@sss.pgh.pa.us>
<20190804195823.qi7vntgybfgitdnn@development>
<27954.1564950312@sss.pgh.pa.us>
<20190804204848.7f7ypsbijpgxojxx@development>
On Sun, Aug 04, 2019 at 10:48:48PM +0200, Tomas Vondra wrote:
>On Sun, Aug 04, 2019 at 04:25:12PM -0400, Tom Lane wrote:
>>Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
>>>On Sun, Aug 04, 2019 at 03:16:12PM -0400, Tom Lane wrote:
>>>>Isn't the issue here the interaction between log_transaction_sample_rate
>>>>and log_min_duration_statement?
>>
>>>No, that interaction only affects statement-level sampling.
>>
>>OK, I was confusing the features.
>>
>>>For transaction-level sampling we do the sampling independently of the
>>>statement duration, i.e. we when starting a transaction we determine
>>>whether the whole transaction will be sampled. It has nothing to do with
>>>the proposed log_statement_sample_limit.
>>
>>So, to clarify: our plan is that a given statement will be logged
>>if any of these various partial-logging features says to do so?
>>
>
>Yes, I think that's the expected behavior.
>
>- did it exceed log_min_duration_statement? -> log it
>- is it part of sampled xact? -> log it
>- maybe sample the statement (to be reverted / reimplemented)
>
>>(And the knock on HEAD's behavior is exactly that it breaks that
>>independence for log_min_duration_statement.)
>>
>
>Yeah. There's no way to use sampling, while ensure logging of all
>queries longer than some limit.
>
FWIW I've reverted the log_statement_sample_rate (both from master and
REL_12_STABLE). May the buildfarm be merciful to me.
I've left the log_transaction_sample_rate in, as that seems unaffected
by this discussion.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: tomas.vondra@2ndquadrant.com, tgl@sss.pgh.pa.us, adrien.nayrat@anayrat.info, pgsql-hackers@lists.postgresql.org
Subject: Re: idea: log_statement_sample_rate - bottom limit for sampling
In-Reply-To: <20190804214154.tbr5pbg5wss2adfu@development>
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