Understanding Mysql Thread States for better performance.

The following list describes thread State values that are associated with general query processing.

·          After create

This occurs when the thread creates a table (including internal temporary tables), at the end of the function that creates the table. This state is used even if the table could not be created due to some error.

·          Analyzing

The thread is calculating a MyISAM table key distributions (for example, for ANALYZE TABLE).

·          checking permissions

The thread is checking whether the server has the required privileges to execute the statement.

·          Checking table

The thread is performing a table check operation.

·          cleaning up

The thread has processed one command and is preparing to free memory and reset certain state variables.

·          closing tables

The thread is flushing the changed table data to disk and closing the used tables. This should be a fast operation. If not, you should verify that you do not have a full disk and that the disk is not in very heavy use.

·          converting HEAP to MyISAM

The thread is converting an internal temporary table from a MEMORY table to an on-disk MyISAM table.

·          copy to tmp table

The thread is processing an ALTER TABLE statement. This state occurs after the table with the new structure has been created but before rows are copied into it.

·          Copying to group table

If a statement has different ORDER BY and GROUP BY criteria, the rows are sorted by group and copied to a temporary table.

·          Copying to tmp table

The server is copying to a temporary table in memory.

·          Copying to tmp table on disk

The server is copying to a temporary table on disk. The temporary result set has become too large. Consequently, the thread is changing the temporary table from in-memory to disk-based format to save memory.

·          Creating index

The thread is processing ALTER TABLE ... ENABLE KEYS for a MyISAM table.

·          Creating sort index

The thread is processing a SELECT that is resolved using an internal temporary table.

·          creating table

The thread is creating a table. This includes creation of temporary tables.

·          Creating tmp table

The thread is creating a temporary table in memory or on disk. If the table is created in memory but later is converted to an on-disk table, the state during that operation will be Copying to tmp table on disk.

·          deleting from main table

The server is executing the first part of a multiple-table delete. It is deleting only from the first table, and saving columns and offsets to be used for deleting from the other (reference) tables.

·          deleting from reference tables

The server is executing the second part of a multiple-table delete and deleting the matched rows from the other tables.

·          discard_or_import_tablespace

The thread is processing an ALTER TABLE ... DISCARD TABLESPACE or ALTER TABLE ... IMPORT TABLESPACE statement.

·          end

This occurs at the end but before the cleanup of ALTER TABLE, CREATE VIEW, DELETE, INSERT, SELECT, orUPDATE statements.

·          executing

The thread has begun executing a statement.

·          Execution of init_command

The thread is executing statements in the value of the init_command system variable.

·          freeing items

The thread has executed a command. Some freeing of items done during this state involves the query cache. This state is usually followed by cleaning up.

·          Flushing tables

The thread is executing FLUSH TABLES and is waiting for all threads to close their tables.

·          FULLTEXT initialization

The server is preparing to perform a natural-language full-text search.

·          init

This occurs before the initialization of ALTER TABLE, DELETE, INSERT, SELECT, or UPDATE statements. Actions taken by the server in this state include flushing the binary log, the InnoDB log, and some query cache cleanup operations.

For the end state, the following operations could be happening:

§  Removing query cache entries after data in a table is changed

§  Writing an event to the binary log

§  Freeing memory buffers, including for blobs

·          Killed

Someone has sent a KILL statement to the thread and it should abort next time it checks the kill flag. The flag is checked in each major loop in MySQL, but in some cases it might still take a short time for the thread to die. If the thread is locked by some other thread, the kill takes effect as soon as the other thread releases its lock.

·          Locked

The query is locked by another query.

·          logging slow query

The thread is writing a statement to the slow-query log.

·          NULL

This state is used for the SHOW PROCESSLIST state.

·          login

The initial state for a connection thread until the client has been authenticated successfully.

·          Opening tables, Opening table

The thread is trying to open a table. This is should be very fast procedure, unless something prevents opening. For example, an ALTER TABLE or a LOCK TABLE statement can prevent opening a table until the statement is finished. It is also worth checking that your table_cache value is large enough.

·          optimizing

The server is performing initial optimizations for a query.

·          preparing

This state occurs during query optimization.

·          Purging old relay logs

The thread is removing unneeded relay log files.

·          query end

This state occurs after processing a query but before the freeing items state.

·          Reading from net

The server is reading a packet from the network.

·          Removing duplicates

The query was using SELECT DISTINCT in such a way that MySQL could not optimize away the distinct operation at an early stage. Because of this, MySQL requires an extra stage to remove all duplicated rows before sending the result to the client.

·          removing tmp table

The thread is removing an internal temporary table after processing a SELECT statement. This state is not used if no temporary table was created.

·          rename

The thread is renaming a table.

·          rename result table

The thread is processing an ALTER TABLE statement, has created the new table, and is renaming it to replace the original table.

·          Reopen tables

The thread got a lock for the table, but noticed after getting the lock that the underlying table structure changed. It has freed the lock, closed the table, and is trying to reopen it.

·          Repair by sorting

The repair code is using a sort to create indexes.

·          Repair done

The thread has completed a multi-threaded repair for a MyISAM table.

·          Repair with keycache

The repair code is using creating keys one by one through the key cache. This is much slower than Repair by sorting.

·          Rolling back

The thread is rolling back a transaction.

·          Saving state

For MyISAM table operations such as repair or analysis, the thread is saving the new table state to the .MYI file header. State includes information such as number of rows, the AUTO_INCREMENT counter, and key distributions.

·          Searching rows for update

The thread is doing a first phase to find all matching rows before updating them. This has to be done if the UPDATE is changing the index that is used to find the involved rows.

·         Sending data

The thread is reading and processing rows for a SELECT statement, and sending data to the client. Because operations occurring during this this state tend to perform large amounts of disk access (reads), it is often the longest-running state over the lifetime of a given query.

·          setup

The thread is beginning an ALTER TABLE operation.

·          Sorting for group

The thread is doing a sort to satisfy a GROUP BY.

·          Sorting for order

The thread is doing a sort to satisfy a ORDER BY.

·          Sorting index

The thread is sorting index pages for more efficient access during a MyISAM table optimization operation.

·          Sorting result

For a SELECT statement, this is similar to Creating sort index, but for nontemporary tables.

·          statistics

The server is calculating statistics to develop a query execution plan. If a thread is in this state for a long time, the server is probably disk-bound performing other work.

·          System lock

The thread is going to request or is waiting for an internal or external system lock for the table. If this state is being caused by requests for external locks and you are not using multiple mysqld servers that are accessing the same MyISAM tables, you can disable external system locks with the --skip-external-locking option. However, external locking is disabled by default, so it is likely that this option will have no effect. For SHOW PROFILE, this state means the thread is requesting the lock (not waiting for it).

·          Table lock

The next thread state after System lock. The thread has acquired an external lock and is going to request an internal table lock.

·          update

The thread is getting ready to start updating the table.

·          Updating

The thread is searching for rows to update and is updating them.

·          updating main table

The server is executing the first part of a multiple-table update. It is updating only the first table, and saving columns and offsets to be used for updating the other (reference) tables.

·          updating reference tables

The server is executing the second part of a multiple-table update and updating the matched rows from the other tables.

·          User lock

The thread is going to request or is waiting for an advisory lock requested with a GET_LOCK() call. For SHOW PROFILE, this state means the thread is requesting the lock (not waiting for it).

·          Waiting for release of readlock

The thread is waiting for a global read lock obtained by another thread (with FLUSH TABLES WITH READ LOCK) to be released.

·          Waiting for tables, Waiting for table

The thread got a notification that the underlying structure for a table has changed and it needs to reopen the table to get the new structure. However, to reopen the table, it must wait until all other threads have closed the table in question.

This notification takes place if another thread has used FLUSH TABLES or one of the following statements on the table in question: FLUSH TABLES tbl_name, ALTER TABLE, RENAME TABLE, REPAIR TABLE, ANALYZE TABLE, orOPTIMIZE TABLE.

·          Waiting on cond

A generic state in which the thread is waiting for a condition to become true. No specific state information is available.

·          Waiting to get readlock

The thread has issued a FLUSH TABLES WITH READ LOCK statement to obtain a global read lock and is waiting to obtain the lock.

·          Writing to net

The server is writing a packet to the network.