Re: idea: log_statement_sample_rate - bottom limit for sampling
От | Tomas Vondra |
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Тема | Re: idea: log_statement_sample_rate - bottom limit for sampling |
Дата | |
Msg-id | 20190804204848.7f7ypsbijpgxojxx@development обсуждение исходный текст |
Ответ на | Re: idea: log_statement_sample_rate - bottom limit for sampling (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: idea: log_statement_sample_rate - bottom limit for sampling
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Список | pgsql-hackers |
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. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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