Re: Inserting 8MB bytea: just 25% of disk perf used? - Mailing list pgsql-performance

Thanks a lot for the detailed reply.

Matthew Wakeling:

> On Thu, 14 Jan 2010, fkater@googlemail.com wrote:
> > This takes about 50s, so, 800MB/50s = 16MB/s.
> >
> > However the harddisk (sata) could write 43 MB/s in the worst
> > case! Why is write performance limited to 16 MB/s?
>
> Several reasons:
>
> The data needs to be written first to the WAL, in order to provide
> crash-safety. So you're actually writing 1600MB, not 800.

I understand. So the actual throughput is 32MB/s which is
closer to 43 MB/s, of course.

Can I verify that by temporarily disabling WAL writes
completely and see if the thoughput is then doubled?

 Felix