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Re: Planner question - "bit" data types

From: Karl Denninger <karl(at)denninger(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Planner question - "bit" data types
Date: 2009-09-08 00:51:43
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Robert Haas wrote:
> On Sat, Sep 5, 2009 at 8:19 PM, Karl Denninger<karl(at)denninger(dot)net> wrote:
>> There was a previous thread and I referenced it. I don't have the other one
>> in my email system any more to follow up to it.
>> I give up; the attack-dog crowd has successfully driven me off.  Ciao.
> Perhaps I'm biased by knowing some of the people involved, but I don't
> think anyone on this thread has been anything but polite.  It would
> certainly be great if PostgreSQL could properly estimate the
> selectivity of expressions like this without resorting to nasty hacks,
> but it can't, and unfortunately, there's really no possibility of that
> changing any time soon.  Even if someone implements a fix today, the
> soonest it will appear in a production release is June 2010.  So, any
> suggestion for improvement is going to be in the form of suggesting
> that you modify the schema in some way.  I know that's not really what
> you're looking for, but unfortunately it's the best we can do.
> As far as I can tell, it is not correct to say that you referenced the
> previous thread.  I do not see any such reference.
> ...Robert
I was asking about modifying the schema.

The current schema is an integer being used as a bitmask.  If the
planner knows how to handle a type of "bit(X)" (and will at least FILTER
rather than NESTED LOOP it on a select, as happens for an Integer used
in this fashion), that change is easier than splitting it into
individual boolean fields.

-- Karl

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