Yeah but anything holding a lock that long can be terminated via statement_timeout can it not?
Well, no? statement_timeout is per-statement, while transaction_timeout is, well, per transaction. If there's a process which is going and has an open transaction and it's holding locks, that can be an issue.
No, what I mean is this:
BEGIN; select * from foo; update bar; delete baz;
Each one of those is subject to statement_timeout, yes? If so, then I don't see a point for transaction timeout. You set statement_timeout for what works for your environment. Once the timeout is reached within the statement (within the transaction), the transaction is going to rollback too.
This implies that a statement used takes a long time. It may not. The lock is held at the transaction level not the statement level, which is why a transaction level timeout is actually more useful than a statement level timeout.
It hard to compare these proposals because any proposal solves slightly different issue and has different advantages and disadvantages. The flat solution probably will by too limited. I see a possible advantages of transaction_timeout (max lock duration), transaction_idle_timeout, statement_timeout. Any of these limits has sense, and can helps with resource management. There is not full substitution.
Regards
Pavel
What I'm most interested in, in the use case which I described and which David built a system for, is getting that lock released from the lower priority process to let the higher priority process run. I couldn't care less about statement level anything.
