On Sat, 02 Jun 2007 00:14:28 +0200, Ron Johnson <ron.l.johnson@xxxxxxx>
wrote:
On 06/01/07 16:38, PFC wrote:
Will the synchronized seq scan patch be able to do this by
issuing all the CREATE INDEX commands at the same time from several
different database connections ?
No, but it could someday.
Actually I tested, it does it right now, albeit unconsciously (pg
doesn't do anything to synchronize the scans, but if you launch the
concurrent connections at the same time and issue all your "create
index" at the same time, only 1 table scan is needed). Maybe if the
tables were bigger, it would lose sync between the 3 concurrent scans
and would end up going slower. That's why I spoke about the
"synchronized scan" patch.
How much of this, though, is from the OS's disk cache? Or are Seq Scans
O_DIRECT and bypass the OS cache?
Well, the file was larger than disk cache, and I checked in vmstat's
number of actual bytes read from disks...
Three threads read the table once, One thread reads the table 3 times.
So it works right now, except it doesn't have (yet) the infrastructure to
keep the scans synchronized, and psql can't open several connections (yet).
