Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

Hi Greg,

On Tuesday 19 January 2010 15:52:25 Greg Stark wrote:
> On Mon, Jan 18, 2010 at 4:35 PM, Greg Stark <gsstark(at)mit(dot)edu> wrote:
> > Looking at this patch for the commitfest I have a few questions.
>
> So I've touched this patch up a bit:
>
> 1) moved the posix_fadvise call to a new fd.c function
> pg_fsync_start(fd,offset,nbytes) which initiates an fsync without
> waiting on it. Currently it's only implemented with
> posix_fadvise(DONT_NEED) but I want to look into using sync_file_range
> in the future -- it looks like this call might be good enough for our
> checkpoints.
Why exactly should that depend on fsync? Sure, thats where most of the pain
comes from now but avoiding that cache poisoning wouldnt hurt otherwise as
well.

I would rather have it called pg_flush_cache_range or such...

> 2) advised each 64k chunk as we write it which should avoid poisoning
> the cache if you do a large create database on an active system.
>
> 3) added the promised but afaict missing fsync of the directory -- i
> think we should actually backpatch this.
I think as well. You need it during recursing as well though (where I had
added it) and not only for the final directory.

> Barring any objections shall I commit it like this?
Other than the two things above it looks fine to me.

Thanks,

Andres