Cardinality from an Explain plan

From: Steve Perry <sperry_at_sprynet.com>
Date: Sat, 19 May 2001 05:18:13 GMT
Message-ID: <pmnN6.5355$y_3.2669085@typhoon.austin.rr.com>

I have a query that returns 300 rows using nested loops, index range scans and unique scans.
standard tables, b-tree indexes, the stats are up to date and the data is freshly loaded.

When I do an explain on the sql, Oracle estimates the cardinality for the statement is 300,000 rows.

I've noticed this same problem for certain bitmapped access paths.

Can somebody explain why Oracle is so far off (1000%) when the metrics should not be skewed.

Solaris 2.6
Oracle 8.1.5 EE
optimizer_mode: first_rows

Thanks,
Steve Received on Sat May 19 2001 - 00:18:13 CDT