Re: [PERFORM] "Hash index" vs. "b-tree index" (PostgreSQL

Quoting Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Mischa Sandberg <mischa(dot)sandberg(at)telus(dot)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.