Re: Plan_table Columns

Cost is a 'meaningless number' measure
of the cost of that step of the query.

Cardinality is the number of rows that
will be returned in that step of the query

Bytes is Cardinality x average row length for that step of the query - useful to the optimizer when the next stage could be a sort.

The position relates to the fact that each row may have several child rows - the position gives you the order in which child rows should appear for each parent. It's actually redundant since the ID column dictates the order of all the rows, nevertheless is gives a nice warm glow when the ID and the
POSITION columns are consistent with
each other.

Try the Oracle Reference Manual, chapter 2, ca. page 114

--

Jonathan Lewis
Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk

eric_peterson_at_maurices.inrg.com wrote in message <7ph8l8$1b7$1_at_nnrp1.deja.com>...
>I am running some explain plans and was looking at columns I don't
>normally use. Does anyone know what the following columns give me?
> POSITION NUMBER(38)
> COST NUMBER(38)
> CARDINALITY NUMBER(38)
> BYTES NUMBER(38)
>I have looked at all four columns on several different statements
>ranging in different levels of complexity. I believe the COST column
>is mainly used for the COST BASED OPTIMIZER and I am assuming that a
>low number is good. What can I expect out of the BYTES field, i.e.
>what does this represent? I have looked at Oracle Documentation but
>have not found a good explanation of what these fields represent.
>
>BTW I am on Oracle 7.3.3.6
>
>Eric Peterson
>Programmer/Analyst DBA
>Maurices Inc.
>eric_peterson_at_maurices.inrg.com
>
>
>Sent via Deja.com http://www.deja.com/
>Share what you know. Learn what you don't.
Received on Thu Aug 19 1999 - 11:13:18 CDT