The theory will make much more sense after you see it in action.
Jared
"Magaliff, Bill" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
09/06/2002 07:23 AM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
cc:
Subject: RE: foreign key indexes and parent-table locking
I agree that that's the best way to see what actually happens, and I will
do
that
but I like to understand the theory, too . . .
-bill
-----Original Message-----
Sent: Thursday, September 05, 2002 5:40 PM
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Importance: High
Bill,
Rather than try to understand that explanation, you may find it
more educational to create a pair of tables with a parent/child
relationship via foreign key.
Put some data in the tables, then do updates and deletes
both with and without FK indexes.
Examine dba_locks while doing so and observe the lock modes.
This will be much easier to understand than the 'documentation'
Jared
"Magaliff, Bill" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
09/05/2002 02:23 PM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
cc:
Subject: foreign key indexes and parent-table locking
Hi,
I'm trying to understand the whole issue of foreign key indexes and
locking.
Found a note on metalink (11828.1) that seems to explain it, but either
it's
not clear or I'm missing something.
"Why then, does an index on the foreign key mean that the shared lock on
the
parent table is not required?
"When a row in the child table is inserted, deleted or has its foreign key
updated, the corresponding index entry/entries is/are also locked. When an
application attempts to delete or update the primary key of a parent row,
it
reads the FIRST corresponding entry in the child's foreign key index
(uncommitted or otherwise) and, if locked, waits for that lock to be
released."
So far so good . . . this next piece, too, seems to make sense:
"If the modified child row is NOT the first occurrence of the foreign key
in
the index then the parent modification must be prevented anyway,
regardless
of the outcome of uncommitted transactions on other child rows with this
key."
But now here's the part that leaves me hanging . . .
"Hence the error can be flagged immediately and so the transaction is not
forced to wait. This mechanism ensures the minimum reads and wait times to
maintain data consistency. "
Can anyone help by either translating this last part or rephrasing it? Or
explaining the issue differnetly?
Thanks
bill
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Magaliff, Bill
INET: [EMAIL PROTECTED]
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Magaliff, Bill
INET: [EMAIL PROTECTED]
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author:
INET: [EMAIL PROTECTED]
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).
