From: Mischa Sandberg <mischa.sandberg@telus.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jim C. Nasby <decibel@decibel.org>
Cc: Neil Conway <neilc@samurai.com>
Cc: Christopher Petrilli <petrilli@gmail.com>
Cc: Ying Lu <ying_lu@cs.concordia.ca>
Cc: pgsql-general@postgresql.org
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL
Date: Tue, 10 May 2005 16:24:01 -0700
Message-ID: <1115767441.4281429124b9b@webmail.telus.net> (raw)
In-Reply-To: <27799.1115765781@sss.pgh.pa.us>
References: <427F6853.90308@cs.concordia.ca>
<427F757A.8000407@samurai.com>
<59d991c405050908271b55e673@mail.gmail.com>
<427F8321.5030702@samurai.com>
<20050509163423.GH35026@decibel.org>
<427F9211.2090008@samurai.com>
<20050509165133.GJ35026@decibel.org>
<427FFCD3.1010803@samurai.com>
<20050510153245.GA31103@decibel.org>
<1115760957.4281293e0155b@webmail.telus.net>
<27799.1115765781@sss.pgh.pa.us>
Quoting Tom Lane <tgl@sss.pgh.pa.us>:
> Mischa Sandberg <mischa.sandberg@telus.net> writes:
> > The PG hash join is the simplest possible: build a hash table in
> memory, and match an input stream against it.
>
> [ raised eyebrow... ] Apparently you've not read the code. It's
> been hybrid hashjoin since we got it from Berkeley. Probably not the
> best possible implementation of the concept, but we do
> understand about spill to disk.
Apologies. I stopped reading around line 750 (PG 8.0.1) in
src/backend/executor/nodeHashjoin.c
if (!node->hj_hashdone)
{
....
/*
* execute the Hash node, to build the hash table
*/
hashNode->hashtable = hashtable;
(void) ExecProcNode((PlanState *) hashNode);
...
and missed the comment:
/*
* Open temp files for outer batches,
*/
Will quietly go and read twice, talk once.
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To: pgsql-performance@postgresql.org
Cc: mischa.sandberg@telus.net, tgl@sss.pgh.pa.us, decibel@decibel.org, neilc@samurai.com, petrilli@gmail.com, ying_lu@cs.concordia.ca, pgsql-general@postgresql.org
Subject: Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL
In-Reply-To: <1115767441.4281429124b9b@webmail.telus.net>
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