maria-discuss team mailing list archive

[Daniel Black <daniel.black@xxxxxxxxxxxxxxxx>]

I was testing out using the query_cache_info plugin (https://mariadb.com/kb/en/mariadb/query_cache_info-plugin/) to pre-cache data into a server after an upgrade. The read only slaves have a fairly high cache hit ratio.

select concat('use ', STATEMENT_SCHEMA, ';', STATEMENT_TEXT, ';') as q INTO OUTFILE '/tmp/qc.txt' FIELDS ESCAPED BY '' TERMINATED BY '' from information_schema.QUERY_CACHE_INFO;
Query OK, 7122 rows affected (0.03 sec)

When loading these it seems the statements have a collation however this isn't stored in the query cache.

$ mysql --force < /tmp/qc.txt > /dev/null
ERROR 1267 (HY000) at line 119: Illegal mix of collations (latin1_bin,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='
ERROR 1267 (HY000) at line 2390: Illegal mix of collations (latin1_bin,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='
ERROR 1267 (HY000) at line 7569: Illegal mix of collations (latin1_bin,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='

Attempts to force this with   --default-character-set={utf8|utf8mb4} also resulted in the same error or same with (echo "set character_set_connection=utf8;"; cat /tmp/qc.txt; ) | time mysql --force..

Are query cache results actually predictable if they have the same statement running in a different session character set/collation?

Anyone see a work around to get the restore file usable on all queries?

Is asking for query cache dump/load as a feature request (similar to innodb_buffer_pool_dump_at_shutdown/innodb_buffer_pool_restore_at_startup) going to be useful to anyone?

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Daniel Black, Engineer @ Open Query (http://openquery.com.au)
Remote expertise & maintenance for MySQL/MariaDB server environments.