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From:Milan Andric Date:August 3 2009 4:16am
Subject:Re: logging slow queries with time
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Nuno, thanks for the tips. I think I will work on getting
mk-query-digest to log to a db table and run it periodically.  Sounds
like a very useful thing to have.

--
Milan

On Sun, Aug 2, 2009 at 10:02 AM, <nuno.tavares@stripped> wrote:
> Hi Milan,
>
> I can see many ways of accomplish what you want:
> * I'm almost sure mk-query-digest will allow you to do so;
> * Either crop the slow query log for the desired timespan (that's a couple of
> shell scripting commands) and run mk-query-digest against it;
> * Set the query log file to a filename which is a link to /dev/null and set a
> cron script to relink it to a real filename at noon and another to relink it to
> /dev/null at 1pm - and then run the scripts you want.
> * In newer versions you can log the slow queries to tables for analysis;
> * Ultimately, you can also try a patched version of mysqldumpslow I was using
> for some time, explained here:
> http://gpshumano.blogs.dri.pt/2009/07/04/analysing-mysql-slow-queries/
>
> In the last two options you'll be logging to a table, so it will be easy to
> select a timed range of queries for consideration.
>
> Hope that helps,
> -NT
>
> Quoting Milan Andric <mandric@stripped>:
>
>> Thanks for the quick replies guys. I won't be pulling queries our of
>> Drupal anytime soon.  The optimizations I will do are minimal.  Sounds
>> like we might just have to live with mediocre performance for now.
>>
>> I will definitely looks further at maatkit though.  I actually ran it
>> mk-query-digest on my slow log and it's pretty amazing output.  Lots
>> there but it might take me a while to digest it all.  And it does have
>> a time span for the queries it spots, like:
>>
>> # Time range 2009-07-31 06:46:48 to 2009-07-31 12:51:21
>>
>> Which is pretty helpful, but ideally I would like to pass args to
>> mk-query-digest to list specific queries that were slow between noon
>> and 1pm for example.  If anyone happens to know how to that it would
>> be helpful.  Otherwise I will keep grokking maatkit tools.
>>
>> Thanks,
>>
>> Milan
>>
>>
>> On Fri, Jul 31, 2009 at 3:14 PM, Johan De Meersman<vegivamp@stripped>
>> wrote:
>> > On Fri, Jul 31, 2009 at 8:14 PM, Milan Andric <mandric@stripped>
> wrote:
>> > Hello,
>> >
>> > I'm serving a burly Drupal install and at some points throughout the
>> > day the mysql threads go way up and iowait peaks.  I'm not sure which
>> > is causing which but during this time the server is unresponsive.  I
>> > would like to determine if there is a poorly optimized query causing
>> > this.
>> >
>> > Drupal is a disaster :-)
>> >
>> > I'm running a dozen drupals, and we've spent the last eight months heavily
>> > optimizing every aspect. It's reasonably good now, but I'd still like to
>> > move away from it.
>> >
>> > Drupal wants to remain compatible with multiple databases, notably both
>> > MySQL and Postgres, and for v7 also Oracle. This means that they can't
>> > optimize their DB layer and use the fancy tricks of a single DB, but must
>> do
>> > things in ways that are compatible with all of them. Postgres doesn't have
>> > autoincrement ? No autoincrement. Mysql doesn't have sequences ? No
>> > sequences.
>> >
>> > Some points:
>> >  - Drupal uses it's own internal unique ID system, not autoincrement,
> for
>> a
>> > number of things. This means that every insert that uses this locks all
>> > other inserts that use this.
>> >  - Drupal has the bothersome tendency to do full table locks around
> some
>> > inserts. This means that even if you move to InnoDB, you'll still get full
>> > table locks. We patched this out according to info found on drupal.org and
>> > other sites.
>> >  - Drupal's innate caching mechanisms are DB bound. Fun and dandy, but
>> > rather irritating if as soon as a busy page expires, a hundred threads all
>> > try to update the same table at the same time. We implemented Memcached.
>> > Patches, at least partial ones, are on drupal.org, but I know we did more
>> > and better in-house.
>> >  - Drupal can cache fine for anonymous users, but once you're logged
> in,
>> > it's nearly impossible to cache. We worked around this by basically making
>> > 'static' cacheable pages, and pulling any dynamic content in through AJAX.
>> >  - Get rid of Drupal's views (in drupal, that is, not wat is called a
> view
>> > in a database). They generate horribly inefficient queries.
>> >  - Full text search modules use MySQL's full text indices, but that's
> not
>> > the best way of doing things. We implemented Sphinx search, there's an
>> > existing drupal module for integration.
>> >
>> > There's lots more that was done, but I can't provide all that info because
>> > a) it's company internal, and b) because I'm not a developer and thus
>> don't
>> > know half of it :-)
>> >
>> > Suffice it to say, I don't like drupal for high-traffic interactive sites.
>> > Get away from it if you can.
>> >
>> >
>> >
>> >
>> >>   I'm logging slow queries but is there a way to see when the
>> >> slow queries take place also?  I'd like to know what queries are
> being
>> >> processed during this window of poor response time, usually around
>> >> noon local time.
>> >
>> > If you want more than just the slow queries, you'll have to enable the
>> full
>> > log. Be aware that this has noticeable impact on performance, and will
>> spam
>> > your disks. Log on different spindles if able, and monitor your disk usage
>> > carefully - mysql stops functioning if it can't write logs.
>> >
>> >
>> >
>> >
>> > --
>> > Celsius is based on water temperature.
>> > Fahrenheit is based on alcohol temperature.
>> > Ergo, Fahrenheit is better than Celsius. QED.
>> >
>>
>> --
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>>
>>
>
>
> --
> Nuno Tavares
> +351 93 618 40 86
> dri Consultoria Informatica
>
>
Thread
logging slow queries with timeMilan Andric31 Jul
  • RE: logging slow queries with timeGavin Towey31 Jul
  • Re: logging slow queries with timeJohan De Meersman31 Jul
    • Re: logging slow queries with timeMilan Andric2 Aug
      • Re: logging slow queries with timenuno.tavares2 Aug
        • Re: logging slow queries with timeMilan Andric3 Aug
          • Re: logging slow queries with timeMilan Andric3 Aug