How to display open transactions in MySQL

Question

I did some queries without a commit. Then the application was stopped.

How can I display these open transactions and commit or cancel them?

Stoichiometric

I think all your transactions are canceled upon disconnect, but not 100% sure. – Eartha

What type of tables are you using? MyISAM, InnoDB, etc? – Virgo

@cdeszaq, obviously not MyISAM it does not have transactions, besides the question really has nothing to do with tables. – Eartha

@Eartha - I only gave MyISAM as an example of the table type. And it very much does matter, because not all tables that support transactions behave the same way with regard to transactions on connection loss. – Virgo

@cdeszaq, The MySQL docs state something very different. – Eartha

Answer 1

How can I display these open transactions and commit or cancel them?

There is no open transaction, MySQL will rollback the transaction upon disconnect.
You cannot commit the transaction (IFAIK).

You display threads using

SHOW FULL PROCESSLIST  

See: http://dev.mysql.com/doc/refman/5.1/en/thread-information.html

It will not help you, because you cannot commit a transaction from a broken connection.

What happens when a connection breaks
From the MySQL docs: http://dev.mysql.com/doc/refman/5.0/en/mysql-tips.html

4.5.1.6.3. Disabling mysql Auto-Reconnect

If the mysql client loses its connection to the server while sending a statement, it immediately and automatically tries to reconnect once to the server and send the statement again. However, even if mysql succeeds in reconnecting, your first connection has ended and all your previous session objects and settings are lost: temporary tables, the autocommit mode, and user-defined and session variables. Also, any current transaction rolls back.

This behavior may be dangerous for you, as in the following example where the server was shut down and restarted between the first and second statements without you knowing it:

Also see: http://dev.mysql.com/doc/refman/5.0/en/auto-reconnect.html

How to diagnose and fix this
To check for auto-reconnection:

If an automatic reconnection does occur (for example, as a result of calling mysql_ping()), there is no explicit indication of it. To check for reconnection, call mysql_thread_id() to get the original connection identifier before calling mysql_ping(), then call mysql_thread_id() again to see whether the identifier has changed.

Make sure you keep your last query (transaction) in the client so that you can resubmit it if need be.
And disable auto-reconnect mode, because that is dangerous, implement your own reconnect instead, so that you know when a drop occurs and you can resubmit that query.

Eartha

This has nothing to do with the question. This only impacts the mysql client, and the OP is talking about a generic application, which likely means his application. Additionally, since the calling application stopped, how would it be able to keep the transaction in memory? – Virgo

@cdeszaq, it has everything to do with the question. An application typically uses mysqld.dll AKA the client And you keep the SQL-statement that contains the full transaction in memory, so that you can play it back when the connection drops. Or you keep it locally on disk, so that upon restart you can resubmit it. – Eartha

There is only my process list command displayed in the SHOW FULL PROCESSLIST. So I guess there are just no open transactions. The funny part is that the autoincrement_ids seem to be lost. – Stoichiometric

@alex the official docs state that, so that is documented behaviour. See the links. – Eartha

Beautiful, Johan. Answered the question, and showed some consequences and the solutions to those consequences, all within a couple of paragraphs. – Git

"upon reconnect" or "upon disconnect"? – Jhvh

Answer 2

Although there won't be any remaining transaction in the case, as @Johan said, you can see the current transaction list in InnoDB with the query below if you want.

SELECT * FROM information_schema.innodb_trx\G

From the document:

The INNODB_TRX table contains information about every transaction (excluding read-only transactions) currently executing inside InnoDB, including whether the transaction is waiting for a lock, when the transaction started, and the SQL statement the transaction is executing, if any.

Burchell

Don't suppose there's any way to tell if the transactions in that table belong to your specific request/session? – Timeout

Please note \G modifier at the end is only useful if you want to format query output within mysql CLI tool. If you use GUI tool like Mysql Workbench, you don't need it. – Mossgrown

@CaptainHypertext the trx_mysql_thread_id column corresponds to the connection ID in the full processlist – Offertory

This works for me. SHOW FULL PROCESSLIST did not show the transactions I want but this statement shows running transaction. – Smegma

Answer 3

You can use show innodb status (or show engine innodb status for newer versions of mysql) to get a list of all the actions currently pending inside the InnoDB engine. Buried in the wall of output will be the transactions, and what internal process ID they're running under.

You won't be able to force a commit or rollback of those transactions, but you CAN kill the MySQL process running them, which does essentially boil down to a rollback. It kills the processes' connection and causes MySQL to clean up the mess its left.

Here's what you'd want to look for:

------------
TRANSACTIONS
------------
Trx id counter 0 140151
Purge done for trx's n:o < 0 134992 undo n:o < 0 0
History list length 10
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0 0, not started, process no 17004, OS thread id 140621902116624
MySQL thread id 10594, query id 10269885 localhost marc
show innodb status

In this case, there's just one connection to the InnoDB engine right now (my login, running the show query). If that line were an actual connection/stuck transaction you'd want to terminate, you'd then do a kill 10594.

Brucite

There is really no need to activly kill a connection after a timeout the connection will be killed anyway and pending transaction from a broken connection cannot be commited so they can be resubmitted without fear of duplications. – Eartha

Better to kill the stuck transactions without waiting for a timeout to clean up - you risk deadlocks otherwise. – Brucite

Ah yes, +1 for that comment. Forgot about those deadlocks for a minute. – Eartha

@MarcB, Why did they change it to show engine innodb status? – Exurb

Answer 4

By using this query you can see all open transactions.

List All:

SHOW FULL PROCESSLIST  

if you want to kill a hang transaction copy transaction id and kill transaction by using this command:

KILL <id>    // e.g KILL 16543

Deportment

transaction <> process – Gaptoothed

Answer 5

With this query below, you can check how many transactions are running currently:

mysql> SELECT count(*) FROM information_schema.innodb_trx;
+----------+
| count(*) |
+----------+
|        3 |
+----------+
1 row in set (0.00 sec)

Tempa