Optimizing Slow Query MySQL InnoDB (Doctrine2)
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12-12-2019 - |
Question
I have a slow query in a Symfony2 project using Doctrine2. I am unsure about what is slowing this down. I have tried to track it down myself, but have run out of ideas. The basic idea is I want to get the first 20 articles from a given feed (by ID) and sort them by the date published. It seems like 1 second is kind of long when I am sorting on about 300 articles on my development machine (production machine has thousands).
The query is:
SELECT
a0_.id AS id0, a0_.guid AS guid1, a0_.title AS title2, a0_.pub_date AS pub_date3,
a0_.summary AS summary4, a0_.content AS content5, a0_.source_url AS source_url6,
a0_.comment_url AS comment_url7, a0_.slug AS slug8, a0_.bitly_url AS bitly_url9,
a0_.thumbnail_id AS thumbnail_id10, a0_.feed_id AS feed_id11,
a0_.author_id AS author_id12
FROM
articles a0_
WHERE
a0_.feed_id = ?
ORDER BY
a0_.pub_date DESC LIMIT 20
Parameters: ['19']
Time: 958.46 ms
Running EXPLAIN, I get this:
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: a0_
type: ref
possible_keys: feed_guid,article_slug_unique,feed
key: feed_guid
key_len: 4
ref: const
rows: 338
Extra: Using where; Using filesort
1 row in set (0.11 sec)
This is my table:
+--------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| guid | varchar(255) | NO | | NULL | |
| title | varchar(255) | NO | | NULL | |
| author_id | int(10) unsigned | YES | MUL | NULL | |
| pub_date | datetime | YES | MUL | NULL | |
| summary | text | YES | | NULL | |
| content | text | NO | | NULL | |
| source_url | varchar(255) | YES | | NULL | |
| comment_url | varchar(255) | YES | | NULL | |
| feed_id | int(10) unsigned | NO | MUL | NULL | |
| slug | varchar(64) | NO | MUL | NULL | |
| bitly_url | varchar(32) | YES | | NULL | |
| thumbnail_id | int(10) unsigned | YES | UNI | NULL | |
+--------------+------------------+------+-----+---------+----------------+
13 rows in set (0.09 sec)
And my indices:
+----------+------------+-----------------------+--------------+--------------+----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+----------+------------+-----------------------+--------------+--------------+------------------------+----------+--------+------+------------+---------+---------------+
| articles | 0 | PRIMARY | 1 | id | A | 51479 | NULL | NULL | | BTREE | | |
| articles | 0 | feed_guid | 1 | feed_id | A | 352 | NULL | NULL | | BTREE | | |
| articles | 0 | feed_guid | 2 | guid | A | 352 | NULL | NULL | | BTREE | | |
| articles | 0 | article_slug_unique | 1 | feed_id | A | 352 | NULL | NULL | | BTREE | | |
| articles | 0 | article_slug_unique | 2 | slug | A | 352 | NULL | NULL | | BTREE | | |
| articles | 0 | UNIQ_BFDD3168FDFF2E92 | 1 | thumbnail_id | A | 51479 | NULL | NULL | YES | BTREE | | |
| articles | 1 | author | 1 | author_id | A | 3677 | NULL | NULL | YES | BTREE | | |
| articles | 1 | feed | 1 | feed_id | A | 1660 | NULL | NULL | | BTREE | | |
| articles | 1 | slug_idx | 1 | slug | A | 51479 | NULL | NULL | | BTREE | | |
| articles | 1 | pub_date_idx | 1 | pub_date | A | 51479 | NULL | NULL | YES | BTREE | | |
+----------+------------+-----------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
10 rows in set (0.68 sec)
And if it helps, here is the Doctrine2 code:
$dql = $this->getEntityManager()
->createQueryBuilder()
->select('art')
->from('MyMainBundle:Article', 'art')
->where('art.feed = :f_id')
->orderBy('art.pubDate', 'DESC');
I'm thinking there must be some way to get MySQL to use my pub_date_idx
index to order the records. I had specifically added the index because I thought I had read that indices should be used for the columns used in ORDER BY
. Please help me in improving this query performance.
Solution
you should have an index for (feed, pubDate) for this query to use index. it should work out if you put it:
CREATE INDEX idx_feed_pub_date ON articles (feed_id, pub_date)