After upgrading two MySQL-Servers which run Master-Slave replication from Percona MySQL 5.5 to Percona MySQL 5.6 an excessive amount of temporary Tables gets created on the slave.
The Master seems to have a similar rate as before.
On the slave we went from an average of roughly 35 per second to about 1000 per second. (these are very rough averages). We have about 3200 Queries per second on this server.
root:/var/lib/mysql# mysql -e "show global status like 'Created_tmp%_tables';" -e "show global status like 'Uptime%';"
+-------------------------+---------+
| Variable_name | Value |
+-------------------------+---------+
| Created_tmp_disk_tables | 1485718 |
| Created_tmp_tables | 1505629 |
+-------------------------+---------+
+---------------------------+-------+
| Variable_name | Value |
+---------------------------+-------+
| Uptime | 1523 |
| Uptime_since_flush_status | 1523 |
+---------------------------+-------+
As you can see, nearly all of the temporary tables are created on disk (~98%). Or rather a RAM-Disk for increased performance.
The configuration in my.cnf hasn't really changed. At most some Options have been renamed to the full length name.
Tweaking tmp_table_size, max_heap_table_size, join_buffer_size and sort_buffer_size doesn't seem to make any difference.
So my question now is what could cause this behaviour?
I've read the Upgrade notes, searched this site and generally googled this issue, but didn't come up with anything that would help me.
If I've forgotten some much needed information, please tell me.
Any help is greatly appreciatet.