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Re: estimating # of distinct values

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Jim Nasby <jim(at)nasby(dot)net>
Cc: Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: estimating # of distinct values
Date: 2011-01-18 02:11:14
Message-ID: AANLkTikysELCLWW9J-UfgUMQ1v8v+-YmpVEL0Fx7qfcf@mail.gmail.com (view raw or flat)
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On Mon, Jan 17, 2011 at 7:56 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
> - Forks are very possibly a more efficient way to deal with TOAST than having separate tables. There's a fair amount of overhead we pay for the current setup.

That seems like an interesting idea, but I actually don't see why it
would be any more efficient, and it seems like you'd end up
reinventing things like vacuum and free space map management.

> - Dynamic forks would make it possible to do a column-store database, or at least something approximating one.

I've been wondering whether we could do something like this by
treating a table t with columns pk, a1, a2, a3, b1, b2, b3 as two
tables t1 and t2, one with columns pk, a1, a2, a3 and the other with
columns pk, b1, b2, b3.  SELECT * FROM t would be translated into
SELECT * FROM t1, t2 WHERE t1.pk = t2.pk.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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