Re: hash join and nested loop join in an oltp query
- From: "Ryan" <ryan.gaffuri@xxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 4 May 2004 20:34:07 -0400
Thanks Dan. What I have noticed recently that in some 3 table joins of the
form
1. one small table
2. two large tables
One of the large tables have multiple 'filters' that lead to just a small
fraction of the records returned. If I index properly where my indexes lead
with these filters, then have the join column last, I am occasionally get
hash joins used by the CBO. When I hint, Nested Loops, the query resulted in
significanlty worse response times and higher logical I/Os. Not quite sure
why. I'm more looking for 'patterns' now than plans, because I can find the
best plan. Its a matter of doing it faster.
The odd thing is that I am seeing 'range scans' with hash joins now. I can't
remember ever seeing this in 8i.
----- Original Message -----
From: <dantow@xxxxxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Tuesday, May 04, 2004 6:01 PM
Subject: Re: hash join and nested loop join in an oltp query
> I have generally found that when hash joins win for sensible OLTP queries,
> queries that return few enough rows to be useful online, you are either
looking
> at quite small tables (in which case either join method will likely be OK,
but
> hash may win), or your nested-loops join order was wrong. If you get the
join
>
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