Merge pull request #404 from percona/ps-9461

PS-9461 [DOCS] - Update kill idle transactions in 8.4

Author: patrickbirch

docs/kill-idle-trx.md

@@ -1,9 +1,60 @@
-# Kill idle transactions
+# Kill idle transaction
 
-This feature limits the age of idle transactions, for all transactional storage
-engines. If a transaction is idle for more seconds than the threshold
-specified, it will be killed. This prevents users from blocking *InnoDB* purge
-by mistake.
+Database servers face a constant challenge: managing resources efficiently while maintaining system stability. The kill idle transactions timeout option is a strategic tool to address this challenge. When you set a time limit, any transaction that stays inactive beyond this limit is automatically stopped.  This action prevents forgotten or stuck transactions from slowing down your database by blocking critical cleanup processes.
+
+The option has the following benefits:
+
+* Automatically terminates long-running, inactive database connections
+
+* Prevents resource hogging by abandoned or forgotten transactions
+
+* Frees up database connection pools
+
+* Reduces unnecessary memory consumption
+
+* Protects against potential connection leaks
+
+* Prevents unnecessary server load from dormant sessions
+
+You must also be consider the following:
+
+* May interrupt legitimate long-running queries
+
+* Requires careful configuration to avoid disrupting critical processes
+
+* Can cause unexpected application behavior if timeout is too aggressive
+
+* Might create additional overhead in monitoring and logging
+
+* Requires precise tuning for different application requirements
+
+
+We recommend that you start with conservative timeout settings and review the logs frequently to track terminated transactions.
+
+This feature works with all types of database storage that support transactions.
+
+## Determine the idle transaction threshold
+
+When setting up a database, you must decide how long to let inactive transactions sit before ending them. This decision affects the database's performance.
+
+| Items to consider                  | Description                                                                                          |
+|---------------------------------|------------------------------------------------------------------------------------------------------|
+| How your database is used       | Look at how long transactions usually take and how often they happen. If most transactions finish quickly, you should end idle ones sooner. |
+| How many things happen at once  | Count how many transactions your system handles simultaneously. If it's a lot, you might need to end idle transactions faster to free up space for new ones. |
+| How it affects speed            | Watch how idle transactions change your database's speed. If they slow things down a lot, ending them sooner can help keep everything running smoothly. |
+| What your business needs        | Consider what's important for your work. Some important transactions might need more time, so you shouldn't end them too quickly. |
+
+## InnoDB purge
+
+The InnoDB purge process in MySQL removes outdated row versions (undo logs) from the system. When a transaction modifies data, InnoDB keeps old row versions for rollback and to support transactions running with multi-version concurrency control (MVCC). Once these versions are no longer needed, the purge process deletes them to free up space and improve performance.
+
+Blocking the InnoDB purge can lead to increased disk space usage and potential performance degradation. This feature helps prevent issues such by:
+
+* Limiting idle transactions: It kills any idle transaction after a specified threshold, ensuring transactions don’t remain idle for too long.
+
+* Preventing mistakes: Users can’t accidentally block the InnoDB purge by leaving transactions idle.
+
+* Improving performance: Keeping the purge process running smoothly helps maintain optimal database performance.
 
 ## System variables
 
@@ -16,6 +67,7 @@ by mistake.
 | Dynamic:       | Yes                |
 | Data type      | Integer            |
 | Default value  | 0 (disabled)       |
-| Units          | Seconds            |
+| Unit           | Seconds            |
+
+If set to a non-zero value, the server kills any idle transaction after it stays idle for this number of seconds.
 
-If non-zero, any idle transaction will be killed after being idle for this many seconds.