I concur. In addition to suggested index I would add a new column in articles table called
body_length, which is going to be updated every time the body column is updated. Add that
column to the composite index mentioned below.
This should speed up the query a lot.
Cheers,
Mihail
On Jan 18, 2011, at 13:03, "Michael Dykman" <mdykman@stripped> wrote:
> Hi Simon,
>
> once you apply functions to a field, an index on that field is pretty
> much useless. For this particular query, I would be tempted to create
> additional fields to store the values of MONTH(articles.created_at)
> and DAY(articles.created_at). Create an index on (month_created,
> day_created) You could just sort by articles.created_at; no need for
> the YEAR function, the result will be the same given your other
> selectors.
>
> Given those adjustments, the query looks righteous enough.
>
> - michael dykman
>
> On Tue, Jan 18, 2011 at 12:22 PM, Simon Wilkinson
> <simon.wilkinson@stripped> wrote:
>> Hi,
>>
>> I am trying to optimize the following query:
>>
>> SELECT articles.* FROM articles INNER JOIN newsletters ON
>> articles.newsletter_id = newsletters.id INNER JOIN users ON users.id =
>> newsletters.user_id WHERE users.id =12 AND MONTH(articles.created_at) = '12'
>> AND DAY(articles.created_at) = '5' ORDER BY YEAR(articles.created_at),
>> LENGTH(articles.body);
>>
>> I am trying to retrieve all the articles created on a specific day of a
>> specific month that belong to a user, ordered by the oldest and then longest
>> article.
>>
>> I have run explain on the query, and get the following:
>>
>>
> +----+-------------+----------+-------+------------------------------------------------------------------------+--------------------------------------------+---------+---------------------+------+----------------------------------------------+
>> | id | select_type | table | type |
>> possible_keys |
>> key | key_len | ref |
>> rows | Extra |
>>
> +----+-------------+----------+-------+------------------------------------------------------------------------+--------------------------------------------+---------+---------------------+------+----------------------------------------------+
>> | 1 | SIMPLE | users | const |
>> PRIMARY |
>> PRIMARY | 4 | const
>> | 1 | Using index; Using temporary; Using filesort |
>> | 1 | SIMPLE | newsletters | ref |
>> PRIMARY,index_newsletters_on_user_id |
>> index_newsletters_on_user_id | 4 |
>> const | 1 | Using index |
>> | 1 | SIMPLE | articles | ref |
>> index_articles_on_newsletter_id,index_articles_on_newsletter_id_and_created_at
>> | index_articles_on_newsletter_id_and_created_at | 4 |
>> my_db.newsletters.id | 3 | Using where |
>>
>>
> +----+-------------+----------+-------+------------------------------------------------------------------------+--------------------------------------------+---------+---------------------+------+----------------------------------------------+
>> 3 rows in set (0.00 sec)
>>
>> This seems pretty decent, and does perform pretty well for some users (~0.5
>> - 1 sec), but for some users (seemingly those with large numbers of
>> articles) the query can take 20 - 30 seconds to run. This seems really slow
>> to me. I tried adding in the index
>> 'index_articles_on_newsletter_id_and_created_at' but the performance doesn't
>> seem to be any different then when it uses just the
>> 'index_articles_on_newsletter_id' index. I think this might be because of
>> the functions I am using on the created_at column to get the day and month
>> from it, making an index on created_at useless in this instance.
>>
>> Running both an 'optimize table entries' and 'analyze table entries' also
>> didn't seem to have any real impact on the performance.
>>
>> I was wondering if anybody had any suggestions for what else I might be able
>> to try, or if there is a better way to search on dates in this manner. Any
>> ideas would be greatly appreciated.
>>
>> Thanks,
>>
>> Simon
>>
>
>
>
> --
> - michael dykman
> - mdykman@stripped
>
> May the Source be with you.
>
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