On 14 November 2011 14:17, Richard Huxton <d...@archonet.com> wrote: > On 14/11/11 10:08, Sergey Konoplev wrote: >> >> On 14 November 2011 12:58, Richard Huxton<d...@archonet.com> wrote: > Let's say you were doing something like "UPDATE unlogged_table SET x=1 WHERE > y=2". If a crash occurs during this command, there's no guarantee that the > affected disk pages were all updated. Worse, a single page might be > partially updated or even have rubbish in it (depending on the nature of the > crash). > > Without the WAL there's no way to check whether the table is good or not, or > even to know what the last updates were. So - the only safe thing to do is > truncate the unlogged tables. > > In the event of a normal shutdown, we can flush all the writes to disk so we > know all the data has been written, so there is no need to truncate.
Thank you for the explanation. Now I understand it. > > -- > Richard Huxton > Archonet Ltd > -- Sergey Konoplev Blog: http://gray-hemp.blogspot.com LinkedIn: http://ru.linkedin.com/in/grayhemp JID/GTalk: gray...@gmail.com Skype: gray-hemp -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
