Re: idea: log_statement_sample_rate - bottom limit for sampling

On Sun, Aug 04, 2019 at 11:41:54PM +0200, Tomas Vondra wrote:
>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(dot)vondra(at)2ndquadrant(dot)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.
>

I've pushed the reworked version of log_statement_sample_rate patch [1].
If I understand correctly, that makes this patch unnecessary, and we
should mark it as rejected. Or do we still need it?

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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