Re: PostmasterIsAlive() in recovery (non-USE_POST_MASTER_DEATH_SIGNAL builds)

On 17/09/2020 12:48, Thomas Munro wrote:
> Hello,
> 
> In commits 9f095299 and f98b8476 we improved recovery performance on
> Linux and FreeBSD but we didn't help other operating systems.  David
> just confirmed for me that commenting out the PostmasterIsAlive() call
> in the main recovery loop speeds up crash recovery considerably on his
> Windows system: 93s -> 70s or 1.32x faster.

Nice speedup!

> So I think we should do
> something like what Heikki originally proposed to lower the frequency
> of checks, on systems where we don't have the ability to skip the
> check completely.  Please see attached.

If you put the counter in HandleStartupProcInterrupts(), it could be a 
long wait if the startup process is e.g. waiting for WAL to arrive in 
the loop in WaitForWALToBecomeAvailable(), or in recoveryPausesHere(). 
My original patch only reduced the frequency in the WAL redo loop, when 
you're actively replaying records.

We could probably do better on Windows. Maybe the signal handler thread 
could wait on the PostmasterHandle at the same time that it waits on the 
signal pipe, and set postmaster_possibly_dead. But I'm not going to work 
on that, and it would only help on Windows, so I'm OK with just adding 
the counter.

- Heikki