Re: Add client connection check during the execution of the query

On Mon, Mar 1, 2021 at 6:18 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> I've done a quick rebase of this the patch and added it to the
> commitfest. No other changes. Several things were mentioned earlier
> that still need to be tidied up.

Rebased again due to bitrot. This time I did some actual work:

1. I didn't like the way it was rearming the timer *in the timer
handler*; I think it should be done in the CFI(), and only if it
determines that you're still running a query (otherwise you'll get
periodic wakeups while you're idle between quieries, which is bad for
the arctic ice cap; we already handle client going away efficiently
between queries with WaitEventSet socket readiness).
2. The timer handler surely has to set the latch to close a race (cf.
other similar handlers; between the CFI() and the beginning of the
sleep, you could handle the signal, set the flag, and then go to sleep
for 100 years).
3. The test might as well use pg_sleep() instead of doing a plpgsql
busy loop of SELECT queries.
4. I prefer the name CLIENT_CONNECTION_CHECK_TIMEOUT instead of
SKIP_CLIENT_CHECK_TIMEOUT; let's make up only one new name for a
concept instead of two.
5. Miniscule doc change.

I put these into a separate patch for ease of review. I don't claim
this is ready -- still needs more testing etc -- but it seems to be
generating the right system calls at the right times now.