On Feb 9, 2010, at 5:00 PM, Jeff Davis wrote: > On Tue, 2010-02-09 at 15:28 -0800, Erik Jones wrote: >> * Set zero_damaged_pages=on, run query that originally showed the >> corruption. This reports 3 different blocks with invalid page headers >> and reports that they are being zero'd out. Unfortunately, >> subsequently querying the table the same blocks show as corrupt. >> Well, after running the query twice with zero_damaged_pages=on the >> first one did go away but the other two remain. > > You probably already did this, but remember to back up your $PGDATA > directory. > > The only thing that I can think of is that the pages are not being > marked as dirty after being zeroed, so it evicts the zeroed page without > actually writing it to disk. That combined with the ring buffer for > sequential scans (which eliminates cache pollution by only using a few > blocks for a sequential scan) would explain why even subsequent queries > encounter the damaged page again. > > VACUUM with zero_damaged_pages on would probably do the trick. > > It's possible that this is a bug. What version are you on? Not sure if it's a bug. Version is 8.3.5 the issue sticks when starting a copy of the data directory with 8.3.8. Anyways, I realized that the dump run with zero_damaged_pages does actually finish. Also, I found that I can actually select all of the data by doing per-day queries to cause data access to be done via index scans since there is a date column indexed; I'm guessing that's because that avoids having to read the data pages' headers? Regardless, I now have two different ways to view the data and decide which works best if there are differences. Erik Jones, Database Administrator Engine Yard Support, Scalability, Reliability 866.518.9273 x 260 Location: US/Pacific IRC: mage2k -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
