Re: New GUC to sample log queries

From: Adrien NAYRAT <adrien(dot)nayrat(at)anayrat(dot)info>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, <vik(dot)fearing(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "Michael Paquier" <michael(at)paquier(dot)xyz>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: New GUC to sample log queries
Date: 2018-11-29 17:14:01
Message-ID: aae0a20c-cb01-62e0-84c9-82f556555040@anayrat.info
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On 11/29/18 2:27 PM, Alvaro Herrera wrote:
>
> =# select name, short_desc, extra_desc, category from pg_settings where category like 'Reporting%When%' ;
> ─[ RECORD 1 ]────────────────────────────────────────────────────────────────────────────────────────────────────
> name │ log_min_duration_statement
> short_desc │ Sets the minimum execution time above which statements will be logged.
> extra_desc │ Zero prints all queries. -1 turns this feature off.
> category │ Reporting and Logging / When to Log
> ─[ RECORD 2 ]────────────────────────────────────────────────────────────────────────────────────────────────────
> name │ log_min_error_statement
> short_desc │ Causes all statements generating error at or above this level to be logged.
> extra_desc │ Each level includes all the levels that follow it. The later the level, the fewer messages are sent.
> category │ Reporting and Logging / When to Log
> ─[ RECORD 3 ]────────────────────────────────────────────────────────────────────────────────────────────────────
> name │ log_min_messages
> short_desc │ Sets the message levels that are logged.
> extra_desc │ Each level includes all the levels that follow it. The later the level, the fewer messages are sent.
> category │ Reporting and Logging / When to Log
> ─[ RECORD 4 ]────────────────────────────────────────────────────────────────────────────────────────────────────
> name │ log_statement_sample_rate
> short_desc │ Fraction of statements to log.
> extra_desc │ 1.0 logs all statements.
> category │ Reporting and Logging / When to Log
>
> The description here seems a bit short on details to me. I would say
> something like "Fraction of statements over log_min_duration_statement
> to log"; otherwise it's not clear why this doesn't apply to
> log_statement. I think the extra_desc should be more verbose too. (Not
> really clear to me what to put in each ... suggestions welcome.)

I totally agree with that.

I like your short_desc, so I propose:

short_desc: "Fraction of statements over log_min_duration_statement to log"
long_desc: "If we only want a sample, use a value between 0 (never log)
and 1.0 (always log)"

If you agree with that, I will send another patch (I will complete
postgresql.conf.sample with the same description).

>
> (More generally, I think we should add a lot more juice to the GUC
> description fields.)
>
> Attached is pgindent fixes for your next submission.
>

Thanks, (I have to remember to pgident patches before submission)

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