How to display open transactions in MySQL

Threads and connections: The movers and shapers

Track thread activity live

You can monitor live thread activity using the SHOW FULL PROCESSLIST command:

SHOW FULL PROCESSLIST;
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This enables you to watch transaction-supporting threads in real time and isolate potentially problematic long-running queries.

Reconnection mechanisms and their quirks

When a reconnection happens, MySQL drops the original connection, leading to a loss of session objects. The built-in auto-reconnect function in MySQL can obscure network glitches or server malfunctions.

To better manage reconnections:

• Disable the default auto-reconnect.
• Develop your own reconnection procedures.
• Store the last executed query on the client-side to re-apply after a disconnection.

mysql_thread_id() can be used to verify that you're still on the original thread when trying to resume a transaction post-disconnection:

SELECT CONNECTION_ID() = mysql_thread_id() AS is_same_thread; -- Are we in the Twilight Zone?
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Pro-level diagnostics: Getting transaction backstories

Transaction internals at your fingertips

Obtain high-level insight into transaction workings, including crucial information about lock requests, through:

SHOW ENGINE INNODB STATUS\G
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Scroll to the TRANSACTIONS section to find granular data on each transaction, such as deadlock stats, rollback segments, and undo logs.

Handling open transactions: Count, kill, chill

Identify current open transactions and get a total count:

SELECT COUNT(*) FROM INFORMATION_SCHEMA.INNODB_TRX; -- How many coffee breaks?
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Using this aggregate metric, you can keep an eye on the overall status of your transaction processing system. To remediate a specific transaction causing a bottleneck, be daring and use KILL <thread_id>:

KILL 12345; -- Bye-bye, 12345! You won't be missed.
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NB: This operation causes an automatic rollback of all changes made by the doomed transaction, releasing any held locks.

Going the extra mile with transactions

Developing a custom reconnection routine

When devising your reconnection scheme, consider the following:

• Using exception handling for lost connections.
• Maintaining state coherency after reconnection.
• Adding error checks and handling for transactional anomalies.

Keeping transactional integrity intact

Consider the following during an unexpected disruption:

• Keeping a transaction log to resurrect state on the client side.
• Implementing idempotent operations to prevent undesirable duplicates or peculiar data discrepancies upon transaction re-submission.

Dealing with stubborn transactions

For unyielding transactions, identify the root cause:

• Overly long-running operations owing to unoptimized queries.
• Shares of lock waits from other transactions.
• Inadequate resources due to hardware constraints or sub-optimal configuration.

Each of these issues can be resolved through targeted responses like query optimization, schema changes, or infrastructure modification.

References