Re: plans for bitmap indexes? - Mailing list pgsql-hackers

From Sailesh Krishnamurthy
Subject Re: plans for bitmap indexes?
Date
Msg-id mjqsm89jt61.fsf@drones.CS.Berkeley.EDU
Whole thread Raw
In response to Re: plans for bitmap indexes?  (Gavin Sherry <swm@linuxworld.com.au>)
List pgsql-hackers
>>>>> "Gavin" == Gavin Sherry <swm@linuxworld.com.au> writes:
   Gavin> I'm uncertain about the potential benefit of   Gavin> this. Isn't/shouldn't the effects of caching be
assisting  Gavin> us here?
 

It all depends on how large your table is, and how busy the system is
(other pressures on the cache). While it's difficult to plan for the
latter you can plan for the former. For the latter you could assume
that the effective cache size is some fraction of the real size to
account for the effects of other queries. Unless you are real sure
that you will never kick out a page from the buffer cache .. 

I believe that for large enough tables this can certainly help .. it
sure is something that many other systems have implemented. 

-- 
Pip-pip
Sailesh
http://www.cs.berkeley.edu/~sailesh




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