Thread: new hash function
I've attached a patch which implements Bob Jenkin's hash function for PostgreSQL. This hash function replaces the one used by hash indexes and the catalog cache. Hash joins use a different, relatively poor-quality hash function, but I'll fix that later. As suggested by Tom Lane, this patch also changes the size of the fixed hash table used by the catalog cache to be a power-of-2 (instead of a prime: I chose 256 instead of 257). This allows the catcache to lookup hash buckets using a simple bitmask. This should improve the performance of the catalog cache slightly, since the previous method (modulo a prime) was slow. In my tests, this improves the performance of hash indexes by between 4% and 8%; the performance when using btree indexes or seqscans is basically unchanged. Unless anyone seems a problem, please apply. Cheers, Neil -- Neil Conway <neilconway@rogers.com> PGP Key ID: DB3C29FC
Attachment
Your patch has been added to the PostgreSQL unapplied patches list at:
http://candle.pha.pa.us/cgi-bin/pgpatches
I will try to apply it within the next 48 hours.
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Neil Conway wrote:
> I've attached a patch which implements Bob Jenkin's hash function for
> PostgreSQL. This hash function replaces the one used by hash indexes and
> the catalog cache. Hash joins use a different, relatively poor-quality
> hash function, but I'll fix that later.
>
> As suggested by Tom Lane, this patch also changes the size of the fixed
> hash table used by the catalog cache to be a power-of-2 (instead of a
> prime: I chose 256 instead of 257). This allows the catcache to lookup
> hash buckets using a simple bitmask. This should improve the performance
> of the catalog cache slightly, since the previous method (modulo a
> prime) was slow.
>
> In my tests, this improves the performance of hash indexes by between 4%
> and 8%; the performance when using btree indexes or seqscans is
> basically unchanged.
>
> Unless anyone seems a problem, please apply.
>
> Cheers,
>
> Neil
>
> --
> Neil Conway <neilconway@rogers.com>
> PGP Key ID: DB3C29FC
[ Attachment, skipping... ]
>
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--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
Patch applied. Thanks. --------------------------------------------------------------------------- Neil Conway wrote: > I've attached a patch which implements Bob Jenkin's hash function for > PostgreSQL. This hash function replaces the one used by hash indexes and > the catalog cache. Hash joins use a different, relatively poor-quality > hash function, but I'll fix that later. > > As suggested by Tom Lane, this patch also changes the size of the fixed > hash table used by the catalog cache to be a power-of-2 (instead of a > prime: I chose 256 instead of 257). This allows the catcache to lookup > hash buckets using a simple bitmask. This should improve the performance > of the catalog cache slightly, since the previous method (modulo a > prime) was slow. > > In my tests, this improves the performance of hash indexes by between 4% > and 8%; the performance when using btree indexes or seqscans is > basically unchanged. > > Unless anyone seems a problem, please apply. > > Cheers, > > Neil > > -- > Neil Conway <neilconway@rogers.com> > PGP Key ID: DB3C29FC [ Attachment, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026