On Fri, 2009-12-04 at 14:47 -0800, Chuck McDevitt wrote: > A curiosity question regarding torn pages: How does this work on file > systems that don't write in-place, but instead always do > copy-on-write? > > My example would be Sun's ZFS file system (In Solaris & BSD). Because > of its "snapshot & rollback" functionality, it never writes a page > in-place, but instead always copies it to another place on disk. How > does this affect the corruption caused by a torn write? > > Can we end up with horrible corruption on this type of filesystem > where we wouldn't on normal file systems, where we are writing to a > previously zeroed area on disk? > > Sorry if this is a stupid question... Hopefully somebody can reassure > me that this isn't an issue.
Think we're still good. Not a stupid question. Hint bits are set while the block is in shared_buffers and setting a hint bit dirties the page, but does not write WAL. Because the page is dirty we re-write the whole block at checkpoint, by bgwriter cleaning or via dirty page eviction. So ZFS is OK, but we do more writing than we want to, sometimes. -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
