Close Idle reserved connections and Rollback Idle transactions

[harshit-gangal]

Currently reserved connections and transactions both are killed after a specific connection timeout from the time of its first use.
This change make use of last connection used time to see if the connection is idle for a certain time.

The current modification changes the logic for both reserved and transaction connection to use last used time. Also, the transaction connections will call rollback rather than closing the underlying connection.

Open Discussion Point:

1. Should transaction connection killer still continue to use created time to identify the idle transactions or it can use the last used time?
2. Should transaction connection killer still continue to close idle transaction or it can be changed to do rollback instead?

[systay]

I don’t think changing the behaviour of the transaction killer is a good idea. Long running transactions are problematic because they lock rows and resources for other users. the same does not really apply to long running reserved connections. I would suggest we keep transaction killing as-is, and only start killing reserved connections by last time used.

Have no opinions on if we should do a ROLLBACK or not.

[sougou]

Agree with @systay on the tx connection timing. That should continue to use start time.