10.14.3 General Thread States

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MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4

10.14.3 General Thread States

The following list describes thread State values that are associated with general query processing and not more specialized activities such as replication. Many of these are useful only for finding bugs in the server.

  • 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. - altering table

The server is in the process of executing an in-place ALTER TABLE. - 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, verify that you do not have a full disk and that the disk is not in very heavy use. - committing alter table to storage engine

The server has finished an in-place ALTER TABLE and is committing the result. - converting HEAP to ondisk

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

For a thread in this state, the Performance Schema can be used to obtain about the progress of the copy operation. See Section 29.12.5, “Performance Schema Stage Event Tables”. - 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 (see Section 10.4.4, “Internal Temporary Table Use in MySQL”). 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 is 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, or UPDATE statements.

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

  • Writing an event to the binary log
  • Freeing memory buffers, including for blobs
  • 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. This state is usually followed by cleaning up. - 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 and the InnoDB log. - 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. - Locking system tables

The thread is trying to lock a system table (for example, a time zone or log table). - logging slow query

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

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

The server is enabling or disabling a table index. - Opening system tables

The thread is trying to open a system table (for example, a time zone or log table). - Opening tables

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_open_cache value is large enough.

For system tables, the Opening system tables state is used instead. - optimizing

The server is performing initial optimizations for a query. - preparing

This state occurs during query optimization. - preparing for alter table

The server is preparing to execute an in-place ALTER TABLE. - 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. - Receiving from client

The server is reading a packet from the client. - 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 multithreaded 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

This state is now included in the Executing state. - Sending to client

The server is writing a packet to the client. - 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 an 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. - starting

The first stage at the beginning of statement execution. - 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 has called mysql_lock_tables() and the thread state has not been updated since. This is a very general state that can occur for many reasons.

For example, the thread is going to request or is waiting for an internal or external system lock for the table. This can occur when InnoDB waits for a table-level lock during execution of LOCK TABLES. 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 has no effect. For SHOW PROFILE, this state means the thread is requesting the lock (not waiting for it).

For system tables, the Locking system tables state is used instead. - 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). - User sleep

The thread has invoked a SLEEP() call. - Waiting for commit lock

FLUSH TABLES WITH READ LOCK is waiting for a commit lock. - waiting for handler commit

The thread is waiting for a transaction to commit versus other parts of query processing. - Waiting for tables

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, or OPTIMIZE TABLE. - Waiting for table flush

The thread is executing FLUSH TABLES and is waiting for all threads to close their tables, or 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, or OPTIMIZE TABLE. - Waiting for lock_type lock

The server is waiting to acquire a THR_LOCK lock or a lock from the metadata locking subsystem, where lock_type indicates the type of lock.

This state indicates a wait for a THR_LOCK:

  • Waiting for table level lock

These states indicate a wait for a metadata lock:

  • Waiting for event metadata lock
  • Waiting for global read lock
  • Waiting for schema metadata lock
  • Waiting for stored function metadata lock
  • Waiting for stored procedure metadata lock
  • Waiting for table metadata lock
  • Waiting for trigger metadata lock

For information about table lock indicators, see Section 10.11.1, “Internal Locking Methods”. For information about metadata locking, see Section 10.11.4, “Metadata Locking”. To see which locks are blocking lock requests, use the Performance Schema lock tables described at Section 29.12.13, “Performance Schema Lock Tables”. - Waiting on cond

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

The server is writing a packet to the network.