Re: Transaction timeout

On Fri, 26 Jan 2024 at 14:44, Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>> On 22 Jan 2024, at 11:23, Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>>
>> Hi, This patch has a CF status of "Needs Review" [1], but it seems
>> there was a CFbot test failure last time it was run [2]. Please have a
>> look and post an updated version if necessary.
> Thanks Peter!
>

Thanks for updating the patch. Here are some comments for v24.

+ <para>
+ Terminate any session that spans longer than the specified amount of
+ time in transaction. The limit applies both to explicit transactions
+ (started with <command>BEGIN</command>) and to implicitly started
+ transaction corresponding to single statement. But this limit is not
+ applied to prepared transactions.
+ If this value is specified without units, it is taken as milliseconds.
+ A value of zero (the default) disables the timeout.
+ </para>
The sentence "But this limit is not applied to prepared transactions" is redundant,
since we have a paragraph to describe this later.

+
+ <para>
+ If <varname>transaction_timeout</varname> is shorter than
+ <varname>idle_in_transaction_session_timeout</varname> or <varname>statement_timeout</varname>
+ <varname>transaction_timeout</varname> will invalidate longer timeout.
+ </para>
+

Since we are already try to disable the timeouts, should we try to disable
them even if they are equal.

+
+ <para>
+ Prepared transactions are not subject for this timeout.
+ </para>

Maybe wrap this with <note> is a good idea.

> I’ve inspected CI fails and they were caused by two different problems:
> 1. It’s unsafe for isaoltion tester to await transaction_timeout within a query. Usually it gets
> FATAL: terminating connection due to transaction timeout
> But if VM is a bit slow it can get occasional
> PQconsumeInput failed: server closed the connection unexpectedly
> So, currently all tests use “passive waiting”, in a session that will not timeout.
>
> 2. In some cases pg_sleep(0.1) were sleeping up to 200 ms. That was making s7 and s8 fail, because they rely on this margin.

I'm curious why this happened.

> I’ve separated these tests into different test timeouts-long and increased margin to 300ms. Now tests run horrible 2431 ms. Moreover I’m afraid that on buildfarm we can have much randomly-slower machines so this test might be excluded.
> This test checks COMMIT AND CHAIN and flow of small queries (Nik’s case).
>
> Also I’ve verified that every "enable_timeout_after(TRANSACTION_TIMEOUT)” and “disable_timeout(TRANSACTION_TIMEOUT)” is necessary and found that case of aborting "idle in transaction (aborted)” is not covered by tests. I’m not sure we need a test for this.

I see there is a test about idle_in_transaction_timeout and transaction_timeout.

Both of them only check the session, but don't check the reason, so we cannot
distinguish the reason they are terminated. Right?

> Japin, Junwang, what do you think?

However, checking the reason on the timeout session may cause regression test
failed (as you point in 1), I don't strongly insist on it.

--
Best regards,
Japin Li.