Re: [RFC] Should smgrtruncate() avoid sending sinval message for temp relations - Mailing list pgsql-hackers

On 2014-07-26 13:58:38 -0400, Tom Lane wrote:

> Andres Freund <andres@2ndquadrant.com> writes:
> > That'd require either renegging on SA_RESTART or
> > using WaitLatchOrSocket() and nonblocking send/recv.
> 
> Yeah, I was wondering about using WaitLatchOrSocket for client I/O too.
> We already have a hook that lets us do the actual recv even when using
> OpenSSL, and in principle that function could do interrupt-service-like
> functions if it got kicked off the recv().

I've started playing with this. Looks clearly worthwile.

I think if we do it right we pretty much can get rid of the whole
prepare_for_client_read() machinery and handle everything via
ProcessInterrupts(). EnableCatchupInterrupt() et al don't really fill me
with joy.

I'm not yet entirely sure where the interrupt processing should happen,
but I guess that'll fall out of the work at some point. The important
bit imo is to *not* not do anything but return with BIO_set_retry_*()
from my_sock_read/write(). That then allows us to implement stuff like
the idle transaction timeout with much fewer problems.

I probably won't finish doing this before leaving on holidays, so nobody
should hesitate to look themselves if interested. If not, I plan to pick
this up again.  I think it's a prerequisite to getting rid of the FATAL
for recovery conflict interrupts which I really would like to do.

> Anything in this line is going to be a bigger change than I'd want to
> back-patch, though.

Agreed. I don't think it will, but it very well could have performance
implications. Besides the obvious risk of bugs...

> Are we OK with not fixing the problem in the back
> branches?  Given the shortage of field complaints, that might be all
> right.

I'm not really comfortable with that. How about simply flagging a couple
contexts to not do the SyncRepWaitForLsn() dance? Possibly just by doing
something ugly like
SetConfigOption('synchronous_commit', 'off', PGC_INTERNAL,
PGC_S_OVERRIDE, GUC_ACTION_LOCAL, true, ERROR)?
during startup, inval and similar transaction commands? Not pretty, but
it looks simple enough to be backpatchable.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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