Hi, Daniel! On May 12, Daniel Black wrote:
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?
Yes, of course. See in sql_cache.{h,cc} the structure Query_cache_query_flags and what's in there. But query_cache_info plugin doesn't show flags.
Anyone see a work around to get the restore file usable on all queries?
Perhaps, extending query_cache_info plugin to show flags? Your script will need to restore a lot more than just a collation. Some flags cannot be set from the sql script whatsoever - but you can skip these entries in your "select concat" query. Regards, Sergei