First query take more then 5 seconds - php

Question

so I have this query
SELECT a.`title`,a.`id`,a.`numvol`,a.`numepi`,a.`release_date`,
(SELECT COUNT(id) FROM `Release` r WHERE r.`article_id`=a.`id`) AS `num_rows`,
(SELECT COUNT(id) FROM `Article_views` av WHERE av.`article_id`=a.`id`) AS `num_rows2`
FROM `Article` a WHERE a.`type` = 'ani' ORDER BY a.`title` ASC
The first load takes up to 5 secs and if I do a refresh it will take about 0.001 sec, is there a way to uniform the loading time?
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY a ALL NULL NULL NULL NULL 567 Using where; Using filesort
3 DEPENDENT SUBQUERY av ALL NULL NULL NULL NULL 5301 Using where
2 DEPENDENT SUBQUERY r ALL NULL NULL NULL NULL 11717 Using where
I tried to do it with join but it didn't work at all so I gave up this way...
Solution
use barmar query. way better :) (and indexes -,-')
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 536 Using temporary; Using filesort
1 PRIMARY a eq_ref PRIMARY PRIMARY 4 r.art.. 1 Using where
1 PRIMARY <derived3> ALL NULL NULL NULL NULL 574 Using where; Using join buffer
3 DERIVED Article_views index NULL article_id 4 NULL 5301 Using index
2 DERIVED Release index NULL article_id 4 NULL 11717 Using index
Thanks guys for your time and the solution :) I guess I need to redo a good part of this old project ahah :)

Answer 1

Try this query instead:
SELECT a.`title`,a.`id`,a.`numvol`,a.`numepi`,a.`release_date`, `num_rows`, `num_rows2`
FROM `Article` a
JOIN (SELECT article_id, COUNT(*) AS num_rows
FROM Release
GROUP BY article_id) r
ON r.article_id = a.id
JOIN (SELECT article_id, COUNT(*) AS num_rows2
FROM Article_views
GROUP BY article_id) av
ON av.article_id = a.id
WHERE a.`type` = 'ani'
ORDER BY a.`title` ASC
In my experience, JOINs are faster than correlated subqueries.
For performance, make sure you have indexes on Release.article_id and Article_views.article_id.

Answer 2

I guess, 2nd try is benefit from SQL QUERY CACHE. I wonder if adding SQL_NO_CACHE, every try took 5 secs?
SELECT SQL_NO_CACHE a.`title`,a.`id`,a.`numvol`,a.`numepi`,a.`release_date`,
....
INDEXES
Oops. you have no relevant INDEX. could you add following indexes?
ALTER TABLE Article ADD INDEX(type);
ALTER TABLE Release ADD INDEX(article_id);
ALTER TABLE Article_views ADD INDEX(article_id);
More Efficient Query
And your Query converted into JOIN. I guess this is much faster than yours. Assuming every Article has Release and Article_views
SELECT a.`title`,a.`id`,a.`numvol`,a.`numepi`,a.`release_date`,
COUNT(r.id) AS `num_rows`,
COUNT(av.id) AS `num_rows2`
FROM `Article` a JOIN Release r ON r.`article_id`=a.`id`
JOIN Article_views av ON av.`article_id`=a.`id`
WHERE a.`type` = 'ani'
GROUP BY a.title, a.id, a.numvol, a.numepi, a.release_date
ORDER BY a.`title` ASC;

Answer 3

That significant improvement on query latency is due to internal MySQL cache functioning.
After the first execution of the query the result set is cached in RAM, so the results second query which just matches the previous, are immediately taken from the RAM without HDD accesses.
There are different points of view about MySQL internal cache, and experts often recommend to disable it in highload production environments using memecached, Redis or some other caching layer instead.
But definitely you should try to optimize performance of your query with caching turned off - 5 seconds is extremely slow.
Try not to use subqueries, cause MySQL optimizer is not performant on them.
Store values of the counters (results of count()) in separate table and update them properly. Then you can use just the counters values in your query without performing heavy database request each time.
Create indexes, for example, for type field.
Use EXPLAIN for further optimizations