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Further second thoughts about idle_session_timeout patch.

Thu, 7 Jan 2021 16:45:08 +0000 (11:45 -0500)

Thu, 7 Jan 2021 16:45:23 +0000 (11:45 -0500)

On reflection, the order of operations in PostgresMain() is wrong.
These timeouts ought to be shut down before, not after, we do the
post-command-read CHECK_FOR_INTERRUPTS, to guarantee that any
timeout error will be detected there rather than at some ill-defined
later point (possibly after having wasted a lot of work).

This is really an error in the original idle_in_transaction_timeout
patch, so back-patch to 9.6 where that was introduced.

src/backend/tcop/postgres.c patch | blob | blame | history

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c

index 2b53ebf97dc48d5210eae7021f2687a489b158f5..28055680aad73486f612226cb3eb6122b45e2aca 100644 (file)

--- a/src/backend/tcop/postgres.c

+++ b/src/backend/tcop/postgres.c

@@ -4323,22 +4323,11 @@ PostgresMain(int argc, char *argv[],

firstchar = ReadCommand(&input_message);

- * (4) disable async signal conditions again.

+ * (4) turn off the idle-in-transaction and idle-session timeouts, if

+ * active. We do this before step (5) so that any last-moment timeout

+ * is certain to be detected in step (5).

- * Query cancel is supposed to be a no-op when there is no query in

- * progress, so if a query cancel arrived while we were idle, just

- * reset QueryCancelPending. ProcessInterrupts() has that effect when

- * it's called when DoingCommandRead is set, so check for interrupts

- * before resetting DoingCommandRead.

- */

- CHECK_FOR_INTERRUPTS();

- DoingCommandRead = false;

- /*

- * (5) turn off the idle-in-transaction and idle-session timeouts, if

- * active.

- *

- * At most one of these two will be active, so there's no need to

+ * At most one of these timeouts will be active, so there's no need to

* worry about combining the timeout.c calls into one.

if (idle_in_transaction_timeout_enabled)

@@ -4352,6 +4341,18 @@ PostgresMain(int argc, char *argv[],

idle_session_timeout_enabled = false;

}

+ /*

+ * (5) disable async signal conditions again.

+ *

+ * Query cancel is supposed to be a no-op when there is no query in

+ * progress, so if a query cancel arrived while we were idle, just

+ * reset QueryCancelPending. ProcessInterrupts() has that effect when

+ * it's called when DoingCommandRead is set, so check for interrupts

+ * before resetting DoingCommandRead.

+ */

+ CHECK_FOR_INTERRUPTS();

+ DoingCommandRead = false;

* (6) check for any other interesting events that happened while we

* slept.

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