oh man I could have used this information a few weeks ago, during
database design......
- "Magaliff, Bill" <Bill.Magaliff_at_lendware.com> wrote:
> Hope you find this useful . . . this info enabled me to drop appx 200
> indexes that had solely been created to avoid supposed parent-table
> locking
> . . .
>
> I'd been trying to determine locking patters on parent-child tables
> with and
> without foreign key indexes. Oracle docs (notably 11828.1, which
> does say
> for Kernel version 7) specifies a shared lock on parent table when
> updating
> child table with no index on foreign key. My testing on 8.1.7
> disproved
> this - index or no index, there was never a lock on the parent table.
>
>
> Having not seen any doc regaring versions 8+, I opened a TAR to
> clarify.
> Wanted to share the outcome:
>
> bill
>
> *************************************************
>
> Oracle rep says:
> We no longer will acquire a share lock on the parent table
>
> The only difference that the FK index makes is that if a delete is
> done on
> the parent table, no FK index results
> in a share lock being acquired on the child table.
>
> An index means that no such lock is acquired.
> (I confirmed this)
>
> I said:
> "from a performance standpoint this should not matter, right? (as
> long as
> none would
> try to modify the child table while the dml on the parent is
> happening, and
> thus have to
> wait for the share lock to be released). And from a r/i perspective,
> the FK
> definition should
> prevent the deletion of a parent value referenced in the child table,
> index
> or no index.
> So as long as I manage who performs DDL on my tables (as a good dba
> should)
> I should safely be able to drop any indexes on FK columns are not
> used in
> where-clauses of joins
> and reduce my overhead."
>
> Oracle rep says:
> "Yes, your assessment is correct. Provided you can manage DDL
> operation, you
> can safely
> drop any indexes on FK columns that are not used in 'where' clauses
> of
> joins."
>
>
>
>
>
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Magaliff, Bill
> INET: Bill.Magaliff_at_lendware.com
>
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Rachel Carmichael
INET: wisernet100_at_yahoo.com
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Received on Fri Sep 13 2002 - 11:48:20 CDT