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 | 20190804214154.tbr5pbg5wss2adfu@development обсуждение исходный текст |
Ответ на | Re: idea: log_statement_sample_rate - bottom limit for sampling (Tomas Vondra <tomas.vondra@2ndquadrant.com>) |
Ответы |
Re: idea: log_statement_sample_rate - bottom limit for sampling
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Список | pgsql-hackers |
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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