Re: simple question on DDL

Hi Rachel,

Good point about the autonomous transactions. If I remember correctly that was new
in 8i.

My general theory on WHY questions is "That's the way they coded it!". They probably could have coded it differently, but they didn't. The important thing is that
it is well documented how it works. If someone mixes ddl and dml they have no basis
to complain about the result.

John

wisernet100_at_yahoo.com wrote:

>remember this "functionality" of committing before a DDL statement has
>been around from the beginning. Autonomous transactions have not. It
>may simply be a case of Oracle not getting around to adding that change
>to the kernel code.
>
>Or, as Kirti quoted from Tom Kyte, that might just be the way they want
>it to work.
>
>
>--- Arup Nanda <arupnanda_at_hotmail.com> wrote:
>
>
>>Dan,
>>
>>If I may, essentially you are saying that changes to data dictionary
>>tables
>>have to be committed immediately regardless of the outcome of the
>>transaction.
>>
>>For instance in the following code, starting with an empty table t1
>>
>>step 1: insert into table t1 values row1
>>step 2: create table t2
>>step 3: insert into table t1 values row2
>>step 4: rollback
>>
>>At this point a select * from t1 will show only row1, since the ddl
>>create
>>table t2 has inserted a commit. However, the point is, my transaction
>>should
>>have been from step 1 through step 4, not fromn step 3 through 4. The
>>DDL
>>broke my txn at step 2 and another transaction started from there.
>>The data
>>dictionary tables were updated and they should be committed; but that
>>commit
>>could have been done via an "autonomous transaction", not in the same
>>
>>transaction the user issued.
>>
>>The more I think about it, I see no point why a DDL should insert a
>>commit.
>>This is different from saying that DDL itself may issue a commit to
>>its
>>seprate transaction to update the catalog. Any thoughts on that?
>>
>>Arup
>>
>>
>>
>>>From: "Fink, Dan" <Dan.Fink_at_mdx.com>
>>>Reply-To: ORACLE-L_at_fatcity.com
>>>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>>>Subject: RE: simple question on DDL
>>>Date: Wed, 22 Jan 2003 14:18:57 -0800
>>>MIME-Version: 1.0
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>>>
>>>
>>22 Jan
>>
>>
>>>2003 15:13:04 -0800
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>>>
>>(PST)
>>
>>
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>>>
>>>
>>00537F3B;
>>
>>
>>>Wed, 22 Jan 2003 14:18:57 -0800
>>>Message-ID: <F001.00537F3B.20030122141857_at_fatcity.com>
>>>X-Comment: Oracle RDBMS Community Forum
>>>X-Sender: "Fink, Dan" <Dan.Fink_at_mdx.com>
>>>Sender: root_at_fatcity.com
>>>Errors-To: ML-ERRORS_at_fatcity.com
>>>Organization: Fat City Network Services, San Diego, California
>>>X-ListServer: v1.0g, build 72; ListGuru (c) 1996-2001 Bruce A.
>>>
>>>
>>Bergman
>>
>>
>>>Precedence: bulk
>>>Return-Path: root_at_fatcity.cts.com
>>>X-OriginalArrivalTime: 22 Jan 2003 23:13:04.0174 (UTC)
>>>FILETIME=[D0E4CCE0:01C2C26B]
>>>
>>>Don't forget that extent allocation also affects the extent map for
>>>
>>>
>>the
>>
>>
>>>segment and possibly the high water mark. The hwm can be set without
>>>allocating another extent and allocation of an extent may not alter
>>>
>>>
>>the hwm
>>
>>
>>>(if you manually allocate an extent). If I deallocate space from an
>>>
>>>
>>object,
>>
>>
>>>I will alter the rows in fet$ and uet$ but not update the hwm. Make
>>>
>>>
>>sense?
>>
>>
>>>As for the ATOMICITY of the transaction, this is usually used to
>>>
>>>
>>describe
>>
>>
>>>the changes to data of interest. I don't think it is used to
>>>
>>>
>>describe any
>>
>>
>>>underlying data dictionary changes. Thus the answer is Yes (for 99%
>>>
>>>
>>of the
>>
>>
>>>Oracle techies) and No (for the 1% of us who really like to know
>>>
>>>
>>exactly
>>
>>
>>>what is going on under the covers).
>>>
>>>Thanks for a great question, it brought up a subject that I had
>>>
>>>
>>never
>>
>>
>>>thought about. Yee-Haw! I learned someting today!
>>>
>>>Cheers,
>>>Dan
>>>
>>>-----Original Message-----
>>>Sent: Wednesday, January 22, 2003 2:04 PM
>>>To: Multiple recipients of list ORACLE-L
>>>
>>>
>>>
>>>Thanks Dan. The gist of your response was that all changes to the
>>>
>>>
>>data
>>
>>
>>>dictionary are immediately commited. Seems to make sense to me.
>>>
>>>
>>Maybe,
>>
>>
>>>thats one reason why one cannot free space below the high water
>>>
>>>
>>mark. Coz
>>
>>
>>>changes to UET$ has been committed, even though the data was rolled
>>>
>>>
>>back.
>>
>>
>>>I sent an email to one of my senior DBA friends, posing the same
>>>
>>>
>>question,
>>
>>
>>>and he replied with a one liner "To make the transaction as ATOMIC
>>>
>>>
>>as
>>
>>
>>>possible - They either run completely, or not at all". Now, does
>>>
>>>
>>that mean
>>
>>
>>>the Insert, update and delete statements are not ATOMIC? For on a
>>>
>>>
>>rollback,
>>
>>
>>>changes to the data dictionary are commited, whereas the data is
>>>
>>>
>>rolled
>>
>>
>>>back.
>>>
>>>Thanks
>>>Raj
>>>
>>>
>>>
>>>
>>>
>>>
>>> "Fink, Dan"
>>>
>>> <Dan.Fink_at_mdx To: Multiple
>>>
>>>
>>recipients of
>>
>>
>>>list
>>>ORACLE-L <ORACLE-L_at_fatcity.com>
>>> .com> cc:
>>>
>>> Sent by: Subject: RE: simple
>>>
>>>
>>question
>>
>>
>>>on
>>>DDL
>>> root_at_fatcity.
>>>
>>> com
>>>
>>>
>>>
>>>
>>>
>>> January 22,
>>>
>>> 2003 02:16 PM
>>>
>>> Please
>>>
>>> respond to
>>>
>>> ORACLE-L
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>Take the case of an insert (we'll call tx1), where space allocation
>>>
>>>
>>is
>>
>>
>>>required. As you insert records, the table allocated additional
>>>
>>>
>>extents
>>
>>
>>>(updating fet$ (free extent table) and uet$ (used extent table) in
>>>
>>>
>>the data
>>
>>
>>>dictionary). These updates to the data dictionary are implicitly
>>>
>>>
>>committed,
>>
>>
>>>even if you issue an explicit rollback for the insert statement.
>>>
>>>
>>Imagine if
>>
>>
>>>the dd changes are not immediately committed. Let's say another tx
>>>
>>>
>>(we'll
>>
>>
>>>call tx2) needs to allocate an extent in the same datafile. If fet$
>>>contains only a single row for the file requested, then tx1 will
>>>
>>>
>>have an
>>
>>
>>>exclusive lock on the row. tx2 needs to also lock the row
>>>
>>>
>>exclusively in
>>
>>
>>>order to update it. Thus, tx2 would wait until tx1 has completed and
>>>released the lock. In the meantime, any transaction that needs to
>>>
>>>
>>allocate
>>
>>
>>>a
>>>new extent in that file will have to wait...and wait...and wait.
>>>
>>>A different strategy is to commit the changes to fet$ and uet$
>>>
>>>
>>immediately.
>>
>>
>>>Then the next tx can access the row and grab space. While this could
>>>
>>>
>>result
>>
>>
>>>in an overallocation of space if the tx is rolled back, it does not
>>>
>>>
>>block
>>
>>
>>>other txs. If space was allocated to an object, and the tx failed,
>>>
>>>
>>there is
>>
>>
>>>a strong probability that this space will be used at some point in
>>>
>>>
>>the
>>
>>
>>>future.
>>>
>>>It seems that the tradeoff here is that the access to the data
>>>
>>>
>>dictionary
>>
>>
>>
>=== message truncated ===
>
>
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