microslow logs slow queries even if not executed

[Arjen Lentz]

When long_query_time is really small, the slow log will also see queries that are not actually executed, for instance because of a syntax error. Naturally this is not desirable behaviour.

The probable cause is actually likely to be with the original slow query log code and not with the microslow patch as such; with second-granularity, no syntax error query would ever take longer than a second to get through the parsing stage....

[Wultsch (wultsch)]

On Tue, Nov 11, 2008 at 10:26 PM, Arjen Lentz <email address hidden> wrote:
> Public bug reported:
>
> When long_query_time is really small, the slow log will also see queries
> that are not actually executed, for instance because of a syntax error.
> Naturally this is not desirable behaviour.
>
> The probable cause is actually likely to be with the original slow query
> log code and not with the microslow patch as such; with second-
> granularity, no syntax error query would ever take longer than a second
> to get through the parsing stage....
>
> ** Affects: ourdelta
> Importance: Undecided
> Status: New
>
> --
> microslow logs slow queries even if not executed
> https://bugs.launchpad.net/bugs/297060
> You received this bug notification because you are a member of OurDelta-
> developers, which is the registrant for OurDelta.
>
> Status in OurDelta - Builds for MySQL: New
>
> Bug description:
> When long_query_time is really small, the slow log will also see queries that are not actually executed, for instance because of a syntax error. Naturally this is not desirable behaviour.
>
> The probable cause is actually likely to be with the original slow query log code and not with the microslow patch as such; with second-granularity, no syntax error query would ever take longer than a second to get through the parsing stage....
>

I think this is not a bug. If a DBA decides that any query over that
takes over some period of time should be logged, and a query (with a
syntax error, or not) takes longer than that period it __should__ be
logged.

As long as the behavior is documented I do not see it as problematic.

--
Rob Wultsch

[Arjen Lentz (arjen-lentz)]

On 12/11/2008, at 4:42 PM, Wultsch wrote:
>> Bug description:
>> When long_query_time is really small, the slow log will also see
>> queries that are not actually executed, for instance because of a
>> syntax error. Naturally this is not desirable behaviour.
>>
>> The probable cause is actually likely to be with the original slow
>> query log code and not with the microslow patch as such; with
>> second-granularity, no syntax error query would ever take longer
>> than a second to get through the parsing stage....
>>
>
> I think this is not a bug. If a DBA decides that any query over that
> takes over some period of time should be logged, and a query (with a
> syntax error, or not) takes longer than that period it __should__ be
> logged.
>
> As long as the behavior is documented I do not see it as problematic.

The slow log is intended for execution time, queries with syntax
errors are not executed.
An error is an error, it already reports back instantly on the client
side... what would be the practical purpose of logging it in the slow
log?

I use a very low long_query_time in training to show how queries are
executed (mem/disk tmp table, mem/disk sort, etc); of course I make
typos on the cmdline client while typing, don't want all that junk
logged.

[Cafuego (cafuego)]

On Wed, 2008-11-12 at 08:32 +0000, Arjen Lentz wrote:
> On 12/11/2008, at 4:42 PM, Wultsch wrote:
> >> Bug description:
> >> When long_query_time is really small, the slow log will also see
> >> queries that are not actually executed, for instance because of a
> >> syntax error. Naturally this is not desirable behaviour.
> >>
> >> The probable cause is actually likely to be with the original slow
> >> query log code and not with the microslow patch as such; with
> >> second-granularity, no syntax error query would ever take longer
> >> than a second to get through the parsing stage....
> >>
> >
> > I think this is not a bug. If a DBA decides that any query over that
> > takes over some period of time should be logged, and a query (with a
> > syntax error, or not) takes longer than that period it __should__ be
> > logged.
> >
> > As long as the behavior is documented I do not see it as problematic.
>
>
> The slow log is intended for execution time, queries with syntax
> errors are not executed.
> An error is an error, it already reports back instantly on the client
> side... what would be the practical purpose of logging it in the slow
> log?
>
> I use a very low long_query_time in training to show how queries are
> executed (mem/disk tmp table, mem/disk sort, etc); of course I make
> typos on the cmdline client while typing, don't want all that junk
> logged.

Suggestion: log_long_parse_time/log_long_parse_fail as extra option.

I can see advantages both ways for DBAs. So why not give them both, and
have a second cfg option that allows them to log queries that spend more
than XXX microseconds in the parser, with whether or not they're
executed as a boolean?

Don't underestimate the need for a DBA to have numbers to beat their
developers over the head with ;-)

- P.
--
Peter Lieverdink counter.li.org #108200 -37.807478, 144.94465
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2.6.27-7-generic #1 SMP Tue Nov 4 19:33:06 UTC 2008 x86_64 GNU/Linux