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分类: Mysql/postgreSQL
2010-08-03 11:34:44
SHOW PROCESSLIST
SHOW [FULL] PROCESSLIST
shows you which threads are running. You can also get this information using the mysqladmin processlist
command. If you have the SUPER
privilege, you can see all threads. Otherwise, you can see only your own threads. See section . If you don't use the FULL
option, then only the first 100 characters of each query will be shown.
Starting from 4.0.12, MySQL reports the hostname for TCP/IP connections in hostname:client_port
format to make it easier to find out which client is doing what.
This command is very useful if you get the 'too many connections' error message and want to find out what's going on. MySQL reserves one extra connection for a client with the SUPER
privilege to ensure that you should always be able to login and check the system (assuming you are not giving this privilege to all your users).
Some states commonly seen in mysqladmin processlist
Checking table
The thread is performing [automatic] checking of the table.
Closing tables
Means that the thread is flushing the changed table data to disk and closing the used tables. This should be a fast operation. If not, then you should check that you don't have a full disk or that the disk is not in very heavy use.
Connect Out
Slave connecting to master.
Copying to tmp table on disk
The temporary result set was larger than tmp_table_size
and the thread is now changing the in memory-based temporary table to a disk based one to save memory.
Creating tmp table
The thread is creating a temporary table to hold a part of the result for the query.
deleting from main table
When executing the first part of a multiple-table delete and we are only deleting from the first table.
deleting from reference tables
When executing the second part of a multiple-table delete and we are deleting the matched rows from the other tables.
Flushing tables
The thread is executing FLUSH TABLES
and is waiting for all threads to close their tables.
Killed
Someone has sent a kill 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 may still take a short time for the thread to die. If the thread is locked by some other thread, the kill will take effect as soon as the other thread releases its lock.
Sending data
The thread is processing rows for a SELECT
statement and is also sending data to the client.
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
.
Opening tables
This simply means that 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
can prevent opening a table until the command is finished.
Removing duplicates
The query was using SELECT DISTINCT
in such a way that MySQL couldn't optimise that distinct away at an early stage. Because of this MySQL has to do an extra stage to remove all duplicated rows before sending the result to the client.
Reopen table
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 now trying to reopen it.
Repair by sorting
The repair code is using sorting to create indexes.
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
.
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.
Sleeping
The thread is wating for the client to send a new command to it.
System lock
The thread is waiting for getting to get a external system lock for the table. If you are not using multiple mysqld servers that are accessing the same tables, you can disable system locks with the --skip-external-locking
option.
Upgrading lock
The INSERT DELAYED
handler is trying to get a lock for the table to insert rows.
Updating
The thread is searching for rows to update and updating them.
User Lock
The thread is waiting on a GET_LOCK()
.
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. To be able to reopen the table it must however wait until all other threads have closed the table in question. This notification happens if another thread has used FLUSH TABLES
or one of the following commands on the table in question: FLUSH TABLES table_name
, ALTER TABLE
, RENAME TABLE
, REPAIR TABLE
, ANALYZE TABLE
or OPTIMIZE TABLE
.
waiting for handler insert
The INSERT DELAYED
handler has processed all inserts and are waiting to get new ones. Most states are very quick operations. If threads last in any of these states for many seconds, there may be a problem around that needs to be investigated.
There are some other states that are not mentioned previously, but most of these are only useful to find bugs in mysqld
.