Re: Group-count estimation statistics

From: Sailesh Krishnamurthy <sailesh(at)cs(dot)berkeley(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Group-count estimation statistics
Date: 2005-01-28 23:42:09
Message-ID: mjqwttxnmsu.fsf@drones.CS.Berkeley.EDU
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>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

Tom> The only real solution, of course, is to acquire cross-column
Tom> statistics, but I don't see that happening in the near
Tom> future.

Another approach is a hybrid hashing scheme where we use a hash table
until we run out of memory at which time we start spilling to disk. In
other words, no longer use SortAgg at all ..

Under what circumstances will a SortAgg consumer more IOs than a
hybrid hash strategy ?

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

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