Aurora MySQL thread states - Amazon Aurora
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Aurora MySQL thread states

The following are some common thread states for Aurora MySQL.

checking permissions

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

checking query cache for query

The server is checking whether the current query is present in the query cache.

cleaned up

This is the final state of a connection whose work is complete but which hasn't been closed by the client. The best solution is to explicitly close the connection in code. Or you can set a lower value for wait_timeout in your parameter group.

closing tables

The thread is flushing the changed table data to disk and closing the used tables. If this isn't a fast operation, verify the network bandwidth consumption metrics against the instance class network bandwidth. Also, check that the parameter values for table_open_cache and table_definition_cache parameter allow for enough tables to be simultaneously open so that the engine doesn't need to open and close tables frequently. These parameters influence the memory consumption on the instance.

converting HEAP to MyISAM

The query is converting a temporary table from in-memory to on-disk. This conversion is necessary because the temporary tables created by MySQL in the intermediate steps of query processing grew too big for memory. Check the values of tmp_table_size and max_heap_table_size. In later versions, this thread state name is converting HEAP to ondisk.

converting HEAP to ondisk

The thread is converting an internal temporary table from an in-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, you can use the Performance Schema to obtain information about the progress of the copy operation.

creating sort index

Aurora MySQL is performing a sort because it can't use an existing index to satisfy the ORDER BY or GROUP BY clause of a query. For more information, see creating sort index.

creating table

The thread is creating a permanent or temporary table.

delayed commit ok done

An asynchronous commit in Aurora MySQL has received an acknowledgement and is complete.

delayed commit ok initiated

The Aurora MySQL thread has started the async commit process but is waiting for acknowledgement. This is usually the genuine commit time of a transaction.

delayed send ok done

An Aurora MySQL worker thread that is tied to a connection can be freed while a response is sent to the client. The thread can begin other work. The state delayed send ok means that the asynchronous acknowledgement to the client completed.

delayed send ok initiated

An Aurora MySQL worker thread has sent a response asynchronously to a client and is now free to do work for other connections. The transaction has started an async commit process that hasn't yet been acknowledged.


The thread has begun running a statement.

freeing items

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


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

master has sent all binlog to slave

The primary node has finished its part of the replication. The thread is waiting for more queries to run so that it can write to the binary log (binlog).

opening tables

The thread is trying to open a table. This operation is fast unless an ALTER TABLE or a LOCK TABLE statement needs to finish, or it exceeds the value of table_open_cache.


The server is performing initial optimizations for a query.


This state occurs during query optimization.

query end

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

removing duplicates

Aurora MySQL couldn't optimize a DISTINCT operation in the early stage of a query. Aurora MySQL must remove all duplicated rows before sending the result to the client.

searching rows for update

The thread is finding all matching rows before updating them. This stage is necessary if the UPDATE is changing the index that the engine uses to find the rows.

sending binlog event to slave

The thread read an event from the binary log and is sending it to the replica.

sending cached result to client

The server is taking the result of a query from the query cache and sending it to the client.

sending data

The thread is reading and processing rows for a SELECT statement but hasn't yet started sending data to the client. The process is identifying which pages contain the results necessary to satisfy the query. For more information, see sending data.

sending to client

The server is writing a packet to the client. In earlier MySQL versions, this wait event was labeled writing to net.


This is the first stage at the beginning of statement execution.


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 while performing other work.

storing result in query cache

The server is storing the result of a query in the query cache.

system lock

The thread has called mysql_lock_tables, but the thread state hasn't been updated since the call. This general state occurs for many reasons.


The thread is preparing to start updating the table.


The thread is searching for rows and is updating them.

user lock

The thread issued a GET_LOCK call. The thread either requested an advisory lock and is waiting for it, or is planning to request it.

waiting for more updates

The primary node has finished its part of the replication. The thread is waiting for more queries to run so that it can write to the binary log (binlog).

waiting for schema metadata lock

This is a wait for a metadata lock.

waiting for stored function metadata lock

This is a wait for a metadata lock.

waiting for stored procedure metadata lock

This is a wait for a metadata lock.

waiting for table flush

The thread is executing FLUSH TABLES and is waiting for all threads to close their tables. Or the thread received notification that the underlying structure for a table changed, so it must reopen the table to get the new structure. To reopen the table, the thread must wait until all other threads have closed the table. This notification takes place if another thread has used one of the following statements on the table: FLUSH TABLES, ALTER TABLE, RENAME TABLE, REPAIR TABLE, ANALYZE TABLE, or OPTIMIZE TABLE.

waiting for table level lock

One session is holding a lock on a table while another session tries to acquire the same lock on the same table.

waiting for table metadata lock

Aurora MySQL uses metadata locking to manage concurrent access to database objects and to ensure data consistency. In this wait event, one session is holding a metadata lock on a table while another session tries to acquire the same lock on the same table. When the Performance Schema is enabled, this thread state is reported as the wait event synch/cond/sql/MDL_context::COND_wait_status.

writing to net

The server is writing a packet to the network. In later MySQL versions, this wait event is labeled Sending to client.