Re:FW: bind vars change explain plan

Barbara,

    The path that the optimizer chooses is based on what values are bound into the variables, but also on what information it has in the data dictionary. If those particular tables/indexes have not been analyzed recently then the optimizer will make wrong decisions. Also init parameters like db_file_multiblock_read_count can prejudice the optimizer to a particular path over others. I would not so much blame the use of bind variables before looking at the data dictionary entries for the table/indexes and the init.ora file. And yes, the optimizer in 7.x was flaky, at best.

Dick Goulet

____________________Reply Separator____________________
Author: "Baker; Barbara" <bbaker_at_denvernewspaperagency.com>
Date:       7/22/2002 7:08 AM

prem.
Never did get an answer to this question. I don't know why using bind variables changed the execution path. My best guess comes from the developer. She thinks that when we supplied the values, the optimizer knew what the range of values would be, and could therefore determine to use the index. With the bind variable, the optimizer did not have a range of values to work with and therefore did not choose the index in the execution path.

I have no knowledge that using bind variables will suppress indexes. Just happened that it did in this case.
Also keep in mind that this particular database is using an old version of Oracle (7.3.4). Optimizer got much better in version 8.

The list helped me out with a work-around, which was to index-hint the index I wanted.

Bind variables are definitely "good guys". I highly recommend you continue with your code changes to include binds.

Good luck.
Barb

> ----------
> From: oraora oraora[SMTP:oraoraora_at_rediffmail.com]
> Reply To: oraora oraora
> Sent: Sunday, July 21, 2002 8:24 PM
> To: bbaker_at_denvernewspaperagency.com
> Subject: Re: bind vars change explain plan
>
> Baker,
>
> sorry i did not read the reply to ur query.
> what was the reply ?
> will using bind vars suppress index ?
> kindly let me know b'coz i have also changed my code to SQL with
> bind vars just now.
>
> Regards,
> prem.
>

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