Ühel kenal päeval, N, 2007-02-15 kell 10:49, kirjutas Heikki Linnakangas:
> We already log tuple removals by normal vacuums. We can't use that wal > entry as it is: if a dead tuple is in the middle of an update chain, it > needs to be unlinked from the chain. But I don't see any particular > problem with that, it just needs to be wal logged like every other data > changing operation. > > Do we actually ever want to remove dead tuples from the middle of the > chain? If a tuple in the middle of the chain is dead, surely every tuple > before it in the chain is dead as well, and we want to remove them as > well. I'm thinking, removing tuples from the middle of the chain can be > problematic, because we'd need to fiddle with the xmin/xmax of the other > tuples to make them match. Or change the tuple-following logic to not do > the xmin=xmax check, but it's a nice robustness feature. What kind of robustness does it provide ? In other words - what failure scenario does this guard against ? I can't see the case where the xmin=xmax check can not succeed, at least not for same page tuples. -- ---------------- Hannu Krosing Database Architect Skype Technologies OÜ Akadeemia tee 21 F, Tallinn, 12618, Estonia Skype me: callto:hkrosing Get Skype for free: http://www.skype.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
