Mysql Buffer Variables

connect_timeout

The number of seconds the mysqld server is waiting for a connect packet before responding with Bad handshake.

join_buffer

The size of the buffer that is used for full joins (joins that do not use indexes). The buffer is allocated one time for each full join between two tables. Increase this value to get a faster full join when adding indexes is not possible. (Normally the best way to get fast joins is to add indexes.)

key_buffer

Index blocks are buffered and are shared by all threads. key_buffer is the size of the buffer used for index blocks. You might want to increase this value when doing many DELETE or INSERT operations on a table with lots of indexes. 

max_allowed_packet

The maximum size of one packet. The message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small to catch big (possibly wrong) packets. You must increase this value if you are using big BLOB columns. It should be as big as the biggest BLOB you want to use.

max_connections

The number of simultaneous clients allowed. Increasing this value increases the number of file descriptors that mysqld requires. 

max_connect_errors

If there is more than this number of interrupted connections from a host this host will be blocked for further connections. You can unblock a host with the command FLUSH HOSTS.

max_join_size

Joins that are probably going to read more than max_join_size records return an error. Set this value if your users tend to perform joins without a WHERE clause that take a long time and return millions of rows.

max_sort_length

The number of bytes to use when sorting BLOB or TEXT values (only the first max_sort_length bytes of each value are used; the rest are ignored).

net_buffer_length

The communication buffer is reset to this size between queries. This should not normally be changed, but if you have very little memory, you can set it to the expected size of a query. (That is, the expected length of SQL statements sent by clients. If statements exceed this length, the buffer is automatically enlarged, up to max_allowed_packet bytes.)

record_buffer

Each thread that does a sequential scan allocates a buffer of this size for each table it scans. If you do many sequential scans, you may want to increase this value.

sort_buffer

Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster ORDER BY or GROUP BY operations. 

table_cache

The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. MySQL needs two file descriptors for each unique open table. See below for comments on file descriptor limits. 

tmp_table_size

If a temporary table exceeds this size, MySQL generates an error of the form The table tbl_name is full. Increase the value of tmp_table_size if you do many advanced GROUP BY queries.

thread_stack

The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. The default is normally large enough.

wait_timeout

The number of seconds the server waits for activity on a connection before closing it.