From: | Atri Sharma <atri(dot)jiit(at)gmail(dot)com> |
---|---|
To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: A better way than tweaking NTUP_PER_BUCKET |
Date: | 2013-06-26 14:39:10 |
Message-ID: | CAOeZVif6MjybNjG-YjLKtyy+3=QEp+fQYG_raQt4aA71aLSqMA@mail.gmail.com |
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On Wed, Jun 26, 2013 at 7:12 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> Atri,
>
> * Atri Sharma (atri(dot)jiit(at)gmail(dot)com) wrote:
>> I just popped in here on Simon's advice to put an idea I had about
>> optimizing hash joins on this thread.
>
> I'd encourage reading the thread a bit first, in the future.. :)
>
Yeah, I actually read a bit(admitted, not much) of the above thread. I
was following it a bit as well.
> I suggested this up-thread already, but it's not really a bloom filter
> as there's only one hash function available- I can't see us requiring
> every data type to provide multiple hash functions. Still, I do think
> breaking the single 32-bit hash key space up into fixed-sized chunks and
> then having a bitfield array which we test against (very similar to how
> the visibility map works) to see if there's any chance that a given hash
> key exists might be valuable. The problem is that, because we don't
> have multiple hash functions, it's not clear how much "empty" space we'd
> actually end up with.
Agreed.
> We could have a bitfield filter (as I described above) created for each
> bucket and then test against that before considering if we actually have
> to go look in that bucket, yes. I'm not sure if that's quite what you
> were thinking, but I can see how a bitfield per bucket might work. If
> you were suggesting something else, please clarify.
Yeah, this is what I wanted.
My point is that I would like to help in the implementation, if possible. :)
Regards,
Atri
--
Regards,
Atri
l'apprenant
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