Re: 8.4 open item: copy performance regression?

Stefan Kaltenbrunner <stefan@kaltenbrunner.cc> wrote: 
> A 25-30% performance regression in our main bulk loading mechanism 
> should at least be explained before the release...
I think a performance regression of that magnitude merits holding up
a release to resolve.
Note that in a follow-up post showing the slow 8.4 copying on Linux,
the copy was 11.7% to 19.3% *faster* on 8.4 when the WAL writing was
suppressed:
http://archives.postgresql.org/pgsql-performance/2009-06/msg00219.php
Extracting from that post:
# I can reproduce that on Linux(CentoS 5.3/x86_64, Nehalem Xeon E5530)
# on 8.4 I get:
# 
# 3m59/4m01/3m56s runtime and a profile of
# 
# samples  %        symbol name
# 636302   19.6577  XLogInsert
# 415510   12.8366  CopyReadLine
# on 8.3.7 I get 2m58s,2m54s,2m55s
# 
# and a profile of:
# 
# samples  %        symbol name
# 460966   16.2924  XLogInsert
# 307386   10.8643  CopyReadLine
# If I do the same test utilizing WAL bypass the picture changes:
# 
# 8.3 runtimes:2m16,2min14s,2min22s
# 8.4 runtime: 2m1s,2m,1m59s
Is there a reason to believe that the XLogInsert part of this *only*
affects bulk loads?
-Kevin