On 9/11/07, Bruce Momjian <[EMAIL PROTECTED]> wrote: > > Heikki Linnakangas wrote: > > > > > Pruning does generate a WAL record at the moment. Maybe you could do > > some kind of a quick pruning without a WAL record. Like just modify the > > ctid of the oldest dead tuple in the chain, or the redirecting line > > pointer if there is one, to point to the latest live tuple, without > > removing the dead tuples or the line pointers. > > I am wondering what you even mean by removing the dead tuples when > pruning. I thought only defragmentation removed tuples. > > Pruning removes intermediate dead tuples by marking their line pointers ~LP_USED and redirecting the root line pointer to the first live/recently_dead tuple in the chain. OTOH defragmentation moves tuples around to repair fragmentation. IOW defragmentation is nothing but calling PageRepairFragmentation on the page.
For example, if we have a HOT chain of 5 tuples: 1 --> 2 --> 3 --> 4 --> 5 of which, 1, 2 and 3 are DEAD, 4 is RECENTLY_DEAD and 5 is LIVE At the end of pruning: - line pointer of 1 is redirected to 4 - line pointers of 2 and 3 are marked ~LP_USED - the offset of 4 and 5 is unchanged At the end of defragmentation: - 4 and 5 are moved to the end of the page to create a larger contiguous free space in the page. Thanks, Pavan -- Pavan Deolasee EnterpriseDB http://www.enterprisedb.com
