Re: cardinalism
From: Joe Celko <71062.1056_at_compuserve.com>
Date: 2000/07/10
Message-ID: <8kclr4$lml$1_at_nnrp1.deja.com>#1/1
Date: 2000/07/10
Message-ID: <8kclr4$lml$1_at_nnrp1.deja.com>#1/1
>> What role does cardinality play as a criterion for selecting the
indexes, and performance tuning? <<
That depends on the product -- some SQL products do not have indexes, but use bit vectors (Nucleus) or hashing (Teradata) instead. But as a general statement, table size allows the optimizer to computer how to use main storage and cache memory. You can get rules like:
- If the table is small enough to fit into main storage, do it.
- How many cache pages does the whole table need?
- Given a SARG, how many rows are expected back from the table.
--CELKO--
Joe Celko, SQL and Database Consultant
When posting, inclusion of SQL (CREATE TABLE ..., INSERT ..., etc)
which can be cut and pasted into Query Analyzer is appreciated.
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Received on Mon Jul 10 2000 - 00:00:00 CEST