Robert Klemme, 19.09.2011 13:13:
On Sun, Sep 18, 2011 at 9:31 PM, Stefan Keller<sfkeller@xxxxxxxxx> wrote:
I'm simply referring to literature (like the intro Ramakrishnan& Gehrke).
I just know that Oracle an Mysql actually do have them too and use it
without those current implementation specific restrictions in
Postgres.
Where exactly do you take that from that Oracle has hash indexes? I
can't seem to find them:
http://download.oracle.com/docs/cd/E11882_01/server.112/e16508/indexiot.htm#sthref293
Are you mixing this up with hash partitioning?
http://download.oracle.com/docs/cd/E11882_01/server.112/e16508/schemaob.htm#sthref443
Or am I missing something?
Maybe he was referring to a hash cluster:
http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/statements_5001.htm
This is a storage option where you can store related rows (e.g. in a parent/child relationship) in the same phyiscal database block based on a hash value. That enables the databse to read parent and child rows with just a single IO.
In the background Oracle probably has something like a hash index to support that.
Thomas
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