Jan Wieck wrote:Manfred Koizar wrote:
> On Thu, 21 Aug 2003 21:10:34 +0530, "Shridhar Daithankar"
> <[EMAIL PROTECTED]> wrote:
>>Point I am trying to make is to tune FSM and autovacuum frequency >>such that you catch all the dead tuples in RAM
> > You might be able to catch the pages with dead tuples in RAM, but
> currently there's no way to keep VACUUM from reading in all the clean
> pages, which can be far more ...
Which leads us to a zero gravity vacuum, that does the lazy vacuum for pages currently available in the buffer cache only. And another pg_stat column telling the number of tuples vacuumed so that an autovac has a chance to avoid IO consuming vacuum runs for relations where 99% of the dead tuples have been caught in memory.
What would be really interesting is to look for dead tuples when you write/discard a buffer page and add them to the FSM --- that is probably the latest time you still have access to the page and has the highest probability of being recyclable.
True, but it's again in the time critical path of a foreground application because it's done by a backend who has to read another page on behalf of a waiting client right now. Also, there is only a small probability that all the pages required to do the index purge for the tuples reclaimed are in memory too. Plus there is still no direct connection between a heap tuples ctid and the physical location of it's index tuples, so purging an index requires a full scan of it, which is best done in bulk operations.
Jan
-- #======================================================================# # It's easier to get forgiveness for being wrong than for being right. # # Let's break this rule - forgive me. # #================================================== [EMAIL PROTECTED] #
---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
