MySQL query cache is enabled but not being used

Question

I've checked the query cache is enabled

mysql> SHOW VARIABLES LIKE 'have_query_cache';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| have_query_cache | YES   |
+------------------+-------+
1 row in set (0.00 sec)

But seems it is not being used

mysql> SHOW STATUS LIKE 'Qcache%';
+-------------------------+----------+
| Variable_name           | Value    |
+-------------------------+----------+
| Qcache_free_blocks      | 1        |
| Qcache_free_memory      | 16759648 |
| Qcache_hits             | 0        |
| Qcache_inserts          | 0        |
| Qcache_lowmem_prunes    | 0        |
| Qcache_not_cached       | 21555882 |
| Qcache_queries_in_cache | 0        |
| Qcache_total_blocks     | 1        |
+-------------------------+----------+
8 rows in set (0.00 sec)

Any reason?

Show us the output from `show variables like 'query_cache%';` — user9517, Jun 05 '14 at 08:15
MySQL Query cache should not be used as [MySQL 8.0: Retired Support for the Query Cache](https://mysqlserverteam.com/mysql-8-0-retiring-support-for-the-query-cache/) -> *"Although MySQL Query Cache was meant to improve performance, it has serious scalability issues and it can easily become a severe bottleneck."* , innoDB 's buffer pool needs to be correctly configured to allow MySQL to be run more like a in memory RDMS.. — Raymond Nijland, Oct 02 '19 at 10:45

score 2 · Accepted Answer · answered Jun 05 '14 at 08:09

2

The system variable query_cache_type needs to be set to non-zero as well, because the presence of the cache doesn't mean it can be used.

answered Jun 05 '14 at 08:09

HBruijn

72,524
21
127
192

1

Sound like this variable defaulted to off in 5.6, not sure why.. – Ryan Jun 05 '14 at 09:10

score 1 · Answer 2 · answered May 02 '17 at 01:23

Please also be aware that not all queries are cacheable.

For example, if a query contains function like NOW(), it would not be cached. Please find the detailed description of which queries cannot be cached: https://dev.mysql.com/doc/refman/5.7/en/query-cache-operation.html

score 0 · Answer 3 · answered Mar 26 '15 at 13:22

You should also check at which position you have written your settings in the configuration file.

My problem was that i placed my qchace settings at the end of the file. Although the settings were reflected by executing mysql> SHOW STATUS LIKE 'Qcache%'; no queries were cached actually.

After placing the settings at a different position in the file and restarting the mysql server it was working.

Here you can see my configuration for MySQL 5.6:

[mysqld]
bind-address=*
#skip-networking
#
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
innodb_buffer_pool_size = 128M
#
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
#
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock

query_cache_type = 1
query_cache_size =256M
thread_concurrency=2
sort_buffer_size=25M
key_buffer=128M

# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

# Recommended in standard MySQL setup
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

score 0 · Answer 4 · answered Jan 21 '16 at 15:27

0

There was a MySQL 5.6 bug, fixed in 5.6.9: "if the db name (or table name) has a '-' (minus), it does not work", on InnoDB only.

answered Jan 21 '16 at 15:27

Victor Sergienko

477
5
15

MySQL query cache is enabled but not being used

4 Answers4

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