On Sun, 2008-01-27 at 15:02 +0000, Gregory Stark wrote: > It occurred to me the other day that synchronized scans could play havoc with > clustered tables. When you dump and reload a table even if it was recently > clustered if any other sequential scans are happening in the system at the > time you dump it the dump could shuffle the records out of order. > > Now the records would still be effectively ordered for most purposes but our > statistics can't detect that. Since the correlation would be poor the restored > database would have markedly different statistics showing virtually no > correlation on the clustered column. > > Perhaps we should have some form of escape hatch for pg_dump to request real > physical order when dumping clustered tables. >
Thank you for bringing this up, it's an interesting point. Keep in mind that this only matters if you are actually running pg_dump concurrently with another scan, because a scan will reset the starting point after completing. Regards, Jeff Davis ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster