ANALYZE and ESTIMATE vs. COMPUTE

Does anyone have suggestions or recommendations about how best to specify percentages for the ANALYZE command?

I'm trying to figure out whether to use ESTIMATE vs. COMPUTE in a set of ANALYZE statements, and if ESTIMATE, what percentage to specify. (This is for Oracle 7.1.) In the course of checking the manuals, I found the following statements:

SQL Language Reference Manual (Dec 1992) - p 4-91:

"SAMPLE specifies the amount of data from the analyzed object Oracle
samples to estimate statistics. If you omit this parameter, Oracle samples 1064 rows."

Application Developer's Guide (Dec 1992) - p 5-11:

"Estimation is often much faster than computation, especially for such
large tables, because estimation never reads more than 1064 rows from the table."

As stated, the ADG description makes it appear that specifying large percentages or numbers of rows > 1064 is useless. I can't help but wonder if some qualifying phrase has dropped out: for example, "...estimation (by default) never reads more than 1064 rows..."

In any case, I'm looking for a rule of thumb. I would prefer to use percentages rather than a number of rows, because the tables are constantly growing, and I want to make sure the sample size is large enough to be valid. On the other hand, some of the tables are > 6,000,000 rows, and I want the analyze to run with reasonable dispatch. If I specify 20% of 6,000,000 rows, ANALYZE may read 1,200,000 rows, and I may be well into the area of diminishing returns.

I would also like to use a standard percentage across the board so I don't have to keep tweaking it.

Suggestions? Comments? Advice? Bitter experience?

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Tad Davis                  215-898-7864 voice
(davist_at_isc.upenn.edu)     215-898-0386 fax