Databases
StackOverflow2013
Postsdbo
POMySQL performance optimization: order by datetime field
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POMySQL performance optimization: order by datetime field
    primarykey
    data
    text
    <p>I have a table with roughly 100.000 blog postings, linked to a table with 50 feeds via an 1:n relationship. When I query both tables with a select statement, ordered by a datetime field of the postings table, MySQL always uses filesort, resulting in very slow query times (>1 second). Here's the schema of the <code>postings</code> table (simplified):</p> <pre><code>+---------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | feed_id | int(11) | NO | MUL | NULL | | | crawl_date | datetime | NO | | NULL | | | is_active | tinyint(1) | NO | MUL | 0 | | | link | varchar(255) | NO | MUL | NULL | | | author | varchar(255) | NO | | NULL | | | title | varchar(255) | NO | | NULL | | | excerpt | text | NO | | NULL | | | long_excerpt | text | NO | | NULL | | | user_offtopic_count | int(11) | NO | MUL | 0 | | +---------------------+--------------+------+-----+---------+----------------+ </code></pre> <p>And here's the <code>feed</code> table:</p> <pre><code>+-------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | type | int(11) | NO | MUL | 0 | | | title | varchar(255) | NO | | NULL | | | website | varchar(255) | NO | | NULL | | | url | varchar(255) | NO | | NULL | | +-------------+--------------+------+-----+---------+----------------+ </code></pre> <p>And here's the query that takes >1 second to execute. Please note that the <code>post_date</code> field has an index, but MySQL isn't using it to sort the postings table:</p> <pre><code>SELECT `postings`.`id`, UNIX_TIMESTAMP(postings.post_date) as post_date, `postings`.`link`, `postings`.`title`, `postings`.`author`, `postings`.`excerpt`, `postings`.`long_excerpt`, `feeds`.`title` AS feed_title, `feeds`.`website` AS feed_website FROM (`postings`) JOIN `feeds` ON `feeds`.`id` = `postings`.`feed_id` WHERE `feeds`.`type` = 1 AND `postings`.`user_offtopic_count` &lt; 10 AND `postings`.`is_active` = 1 ORDER BY `postings`.`post_date` desc LIMIT 15 </code></pre> <p>The result of the <code>explain extended</code> command on this query shows that MySQL is using filesort:</p> <pre><code>+----+-------------+----------+--------+---------------------------------------+-----------+---------+--------------------------+-------+-----------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------+--------+---------------------------------------+-----------+---------+--------------------------+-------+-----------------------------+ | 1 | SIMPLE | postings | ref | feed_id,is_active,user_offtopic_count | is_active | 1 | const | 30996 | Using where; Using filesort | | 1 | SIMPLE | feeds | eq_ref | PRIMARY,type | PRIMARY | 4 | feedian.postings.feed_id | 1 | Using where | +----+-------------+----------+--------+---------------------------------------+-----------+---------+--------------------------+-------+-----------------------------+ </code></pre> <p>When I remove the <code>order by</code> part, MySQL stops using filesort. Please let me know if you have any ideas on how to optimize this query to get MySQL to sort and select the data by using indexes. I have already tried a few things such as creating a combined index on all where/order by fields, as suggested by a few blog postings, but this didn't work either.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USDennis G.
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POMySQL performance optimization: order by datetime field
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POMySQL performance optimization: order by datetime field
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POMySQL performance optimization: order by datetime field
      1. USRobert Swisher
      1. VTFavorite
    1. COI really like the clear and detailed way you asked this.
      singulars
      1. POMySQL performance optimization: order by datetime field
      1. UStpdi
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload