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From:Johan De Meersman Date:August 11 2013 8:32pm
Subject:Re: Concurrent read performance problems
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True, which is why I said I suspected file-based sort :-) At one million rows, that seems
to be an accurate guess, too. Still on the phone, though, and in bed. I'll read the
thread better tomorrow, but you might get some benefit from cutting out the subselect if
that's possible.

If you have plenty of memory, have a look at the max_temp_table_size and max_heap_table
variables, too; those decide when the sort goes to disk.

Johnny Withers <johnny@stripped> wrote:
>Just because it says filrsort doesn't mean it'll create a file on disk.
>Table schema and full query would be helpful here too
>
>http://www.mysqlperformanceblog.com/2009/03/05/what-does-using-filesort-mean-in-mysql/
>On Aug 11, 2013 1:28 PM, "Brad Heller" <brad@stripped> wrote:
>
>> Yes sorry, here's the explain. It was taken from MariaDB 5.5.32.
>Looks like
>> there is a lot of filesort goin' on here. Also note that I'm only
>using the
>> first two fields of the covering index (intentionally).
>>
>>
>>
>+------+-------------+------------------------+-------+------------------------------------+----------------------------+---------+-------------------------------------------------------+---------+-----------------------------------------------------------+
>> | id   | select_type | table                  | type  | possible_keys
>>                | key                        | key_len | ref
>>                                   | rows    | Extra
>>                             |
>>
>>
>+------+-------------+------------------------+-------+------------------------------------+----------------------------+---------+-------------------------------------------------------+---------+-----------------------------------------------------------+
>> |    1 | PRIMARY     | <derived2>             | ALL   | NULL
>>                 | NULL                       | NULL    | NULL
>>                                    | 1004685 | Using temporary; Using
>> filesort                           |
>> |    2 | DERIVED     | accounts               | range |
>> PRIMARY,unique_account_identifiers | unique_account_identifiers | 257
>    |
>> NULL                                                  |       3 |
>Using
>> where; Using index; Using temporary; Using filesort |
>> |    2 | DERIVED     | facts                  | ref   | covering
>>                 | covering                   | 4       |
>> facts.accounts.id                                    |  334895 |
>Using
>> where
>>                               |
>>
>>
>+------+-------------+------------------------+-------+------------------------------------+----------------------------+---------+-------------------------------------------------------+---------+-----------------------------------------------------------+
>>
>>
>> *Brad Heller *| Engineering Lead | Cloudability.com | 541-231-1514 |
>> Skype:
>> brad.heller | @bradhe <http://www.twitter.com/bradhe> |
>> @cloudability<http://www.twitter.com/cloudability>
>>
>>
>> On Sun, Aug 11, 2013 at 8:45 AM, Johan De Meersman
><vegivamp@stripped
>> >wrote:
>>
>> > On my phone now, but it smells of file-based sorting, making disk
>access
>> > the bottleneck. Can you provide the explain?
>> >
>> >
>> > Brad Heller <brad@stripped> wrote:
>> >>
>> >> Hey list, first time posting here so apologies if this is the
>wrong
>> forum
>> >> for this but I'm really out of options on how to solve this
>problem!
>> >>
>> >> *Short version:*
>> >>
>> >>
>> >> 1. High concurrent reads, performing the same well-indexed query
>type to
>> >> the same two tables.
>> >> 2. No additional traffic at all--just reads from these two tables.
>No
>> >> writes anywhere.
>> >> 3. Very fast (sub-second) when server is only servicing one
>request at a
>> >> time.
>> >> 4. Very slow (30s+) when server is servicing 2-3 requests at a
>time.
>> >>
>> >> Questions:
>> >>
>> >> 1. What resource is under contention for servicing read-only
>queries if
>> you
>> >> have a large buffer pool and a plenty-big thread cache?
>> >> 2. What parameters can I tune to increase concurrent reads to
>these two
>> >> tables?
>> >>
>> >> *Long version:*
>> >>
>> >>
>> >> I've got a MySQL server that has only about 50 connections open to
>it at
>> >> any given time. It basically only has one OLAP q
>> >>  uery
>> >> type being ran against
>> >> it that amounts to something like this:
>> >>
>> >> SELECT (3 fields with 1 count) FROM (SELECT (3 fields with 1
>aggregate)
>> >> FROM table INNER JOIN ... WHERE ... GROUP BY ...) dt GROUP BY ...;
>> >>
>> >> These queries are well indexed and run very well
>> individually--sub-second,
>> >> usually even faster. When I run a few of these queries
>simultaneously
>> (2-3
>> >> on my laptop, 6-7 on our production boxes) performance grinds to a
>halt:
>> >> Consistently about 30 seconds to service a query.
>> >>
>> >> Ideally, I'd like to be able to run 50+ of these queries
>concurrently.
>> >>
>> >> I've tried MySQL 5.5.27 and MySQL 5.6.13 and get the same results
>on
>> both
>> >> machines. I've tried tweaking the following my.cnf parameters to
>be
>> higher:
>> >>
>> >> thread_concurrency = 20
>> >> thread_cache_size = 340
>> >> innodb_buffer_pool_size=2G
>> >>
>> >> A few other my.cnf parameters that I have set:
>> >>
>> >> innodb_file_format=Barracuda
>> >> innodb_file_format_max=Barracuda
>> >> innodb_file_per_table=1
>> >> skip-external-locking
>> >> innodb_log_files_in_group=2
>> >> innodb_log_file_size=2000M
>> >> max_allowed_packet=64M
>> >>
>> >> Thanks in advance,
>> >>
>> >> Brad Heller
>> >>
>> >>
>> > --
>> > Sent from Kaiten Mail. Please excuse my brevity.
>> >
>>

-- 
Sent from Kaiten Mail. Please excuse my brevity.
Thread
Concurrent read performance problemsBrad Heller10 Aug
  • Re: Concurrent read performance problemsJohan De Meersman11 Aug
    • Re: Concurrent read performance problemsBrad Heller11 Aug
      • Re: Concurrent read performance problemsJohnny Withers11 Aug
        • Re: Concurrent read performance problemsJohan De Meersman11 Aug
          • Re: Concurrent read performance problemsBrad Heller11 Aug
            • Re: Concurrent read performance problemsJohan De Meersman11 Aug
              • RE: Concurrent read performance problemsRick James12 Aug