Re: Transaction timeout

Hey Andrey,

On Sun, Dec 24, 2023 at 1:14 AM Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
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> > On 22 Dec 2023, at 10:39, Japin Li <japinli(at)hotmail(dot)com> wrote:
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> > I try to split the test for transaction timeout, and all passed on my CI [1].
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> I like the refactoring you did in timeout.spec. I thought it is impossible, because permutations would try to reinitialize FATALed sessions. But, obviously, tests work the way you refactored it.
> However I don't think ignoring test failures on Windows without understanding root cause is a good idea.
> Let's get back to v13 version of tests, understand why it failed, apply your test refactorings afterwards. BTW are you sure that v14 refactorings are functional equivalent of v13 tests?
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> To go with this plan I attach slightly modified version of v13 tests in v16 patchset. The only change is timing in "sleep_there" step. I suspect that failure was induced by more coarse timer granularity on Windows. Tests were giving only 9 milliseconds for a timeout to entirely wipe away backend from pg_stat_activity. This saves testing time, but might induce false positive test flaps. So I've raised wait times to 100ms. This seems too much, but I do not have other ideas how to ensure tests stability. Maybe 50ms would be enough, I do not know. Isolation runs ~50 seconds now. I'm tempted to say that 200ms for timeouts worth it.
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> As to 2nd step "Try to enable transaction_timeout during transaction", I think this makes sense. But if we are doing so, shouldn't we also allow to enable idle_in_transaction timeout in a same manner? Currently we only allow to disable other timeouts... Also, if we are already in transaction, shouldn't we also subtract current transaction span from timeout?
> I think making this functionality as another step of the patchset was a good idea.
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> Thanks!
Seems V5~V17 doesn't work as expected for Nikolay's case:

postgres=# set transaction_timeout to '2s';
SET
postgres=# begin; select pg_sleep(1); select pg_sleep(1); select
pg_sleep(1); select pg_sleep(1); select pg_sleep(1); commit;
BEGIN

The reason for this seems the timer has been refreshed for each
command, xact_started along can not indicate it's a new
transaction or not, there is a TransactionState contains some
infos.

So I propose the following change, what do you think?

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index a2611cf8e6..cffd2c44d0 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -2746,7 +2746,7 @@ start_xact_command(void)
StartTransactionCommand();

/* Schedule or reschedule transaction timeout */
- if (TransactionTimeout > 0)
+ if (TransactionTimeout > 0 &&
!get_timeout_active(TRANSACTION_TIMEOUT))
enable_timeout_after(TRANSACTION_TIMEOUT,
TransactionTimeout);

xact_started = true;

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> Best regards, Andrey Borodin.

--
Regards
Junwang Zhao