Optimizing

When it comes to SQL Query tuning with customers we often get the slow running SQL query and possibly, in good cases, also the table structure. But very often, for various reasons, we do not get the data.

SQL query tuning on an empty table or a table with only little data is not really fun because either the results of the optimizer have nothing to do with reality or the response times do not really show if your change has improved anything. For example if your query response time before the change was 2 ms …

Binlog format MIXED changes the binary log format (ROW or STATEMENT) depending on the queries (deterministic or not). This makes it impossible to define 100% correctly working binary log filter rules.

If the variable flush_time is set to a non-zero value, all tables are closed (and flushed) every flush_time seconds to disk. This can cause unnecessary and high I/O spikes.

For further information consult MariaDB or MySQL documentation.

The Table Open Cache (table_open_cache or old name table_cache) is a cache to store file handles for all threads. The actual value of cache entries can be seen with the global status of open tables (Open_tables).
Increasing table_open_cache increases the number of file descriptors (open_files_limit) that MySQL requires.
You can check whether you need to increase the Table Open Cache by checking Open_tables and Opened_tables. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which …