Oracle 8i locking and timeout

Hi,
I am talking to an Oracle 8.1.7 db through Perl DBI for a certain Web Application.
In the back-end, a script is invoked every hour to sync parts of this db, with the master db. The sync'ing script takes quite a while to complete and it consists of a single transaction ( several update statements followed by a single commmit at the very end).
Now, I want to know what happens to any user who tries to modify something through the web-interface. If a query from the web-interface finds that a row is locked by the syncing script, how long will it wait before a timeout? ( if any timeout occurs at all, in the first place ! ). Can I control this timeout?
Please repond ASAP.
Thanks in advance,
Rajesh

How much control do you have over the SQL being generated? There is a keyword 'NOWAIT' that can be added to a statement indicating that it shouldn't wiat for resources-- if it can't lock them immediately, it returns an ORA-00054 (if memory serves) resource locked and NOWAIT specified. Otherwise, by default, the statement will wait indefinitely.
In ODBC, you can specify a query timeout that will kill all queries after some amount of time.
Justin

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Here is what Oracle defines an Enqueue to be in the 9.2 Glossary >>
enqueue
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I am trying to do the following:
Updating 5M rows in multiple database writer thread using OCI. I have not set any Oracle parallel execution related parameters yet.
However, it is found that there is no performance improvement in doing this in multiple threads.
My questions:
1. Does Oracle lock the table during each update? I think it does and that is why there is no performance enhancement.
- If yes, is there any way to tell Oracle not to lock the table during updates. As it is, my threads will never update the same row in parallel.
2. Is the way out is to do the following?
- Partition the table
- Do an "ALTER SESSION ENABLE PARALLEL DML"
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3. Is there any OCI way of doing this?
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~Sri

I am trying to do the following:
Updating 5M rows in multiple database writer thread using OCI. I have not set any Oracle parallel execution related parameters yet.
However, it is found that there is no performance improvement in doing this in multiple threads.
My questions:
1. Does Oracle lock the table during each update? I think it does and that is why there is no performance enhancement.
- If yes, is there any way to tell Oracle not to lock the table during updates. As it is, my threads will never update the same row in parallel.Unless you're explicitly locking the table, Oracle won't lock it. Oracle doesn't ever escalate row locks to table locks.
My guess is that something in your system is bottlenecked. Perhaps your disk, CPU, or RAM is maxed out. Perhaps your system is busy waiting to switch redo logs. There are lots of potential bottlenecks here, you'd have to do some investigation to figure out what's taking so long.
One quick thing you might try is to use the /*+ append */ hint (i.e. insert /*+ append */ into table (your query here)). This tells the database to do a parallel direct path load, avoiding most redo log generation. This improves the speed, but isn't particularly friendly for database recovery. Make sure you read the documentation on this hint before you use it.
You may also be able to change your SQL to use the bulk collection syntax.
I'd also take a look at this bit of the Oracle documentation, "Serial and Parallel INSERT"
<http://technet.oracle.com/docs/products/oracle8i/doc_library/817_doc/server.817/a76965/c21dlins.htm#2507>
There's a pretty good asktom article over here. Search the site and you'll find lots of info on this sort of thing.
<http://asktom.oracle.com/pls/ask/f?p=4950:8:::::F4950_P8_DISPLAYID:1119033812977>
2. Is the way out is to do the following?
- Partition the table
- Do an "ALTER SESSION ENABLE PARALLEL DML"
- Fire updatesI'm assuming that you have the partitioning options in your database. If so, this is likely to be faster, though I'm not sure by how much. Have you benchmarked a test to see? Of course, if you account for the time to partition the table, you're likely to remove all of your performance gain.
Also, unless you are able to spread your inserts across the various partitions, you're unlikely to see any performance benefit.
This strikes me as a pretty drastic approach.
3. Is there any OCI way of doing this?Well, you could execute the SQL above against the table from OCI. I'd recommend doing this sort of thing from SQL*Plus or something of that genre, though, simply because folks may get upset at you if your application partitions their tables for them.
Thanks in advance,
~Sri

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I would like to understand what is major difference between Dead Locks and Blocking Locks in Oracle. If someone could explain or point me to good web Link I would really appreciate
Thanks.

Tony's advise is very good.
In simple terms a blocking lock is a lock being held by one session that is preventing another session from performing an DML operation on the same data until the holding session commits or rollbacks.
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Locking and blocking - puzzlement.

I have a table - relatively simple
CREATE TABLE Sysstat
M_Time     DATE,
Usr_pct    NUMBER(10, 0),
Sys_pct    NUMBER(10, 0),
<a few more NUMBER(10, 0) deleted...
CONSTRAINT Sysstat_PK PRIMARY KEY (M_Time)
);Issue (From an SQLPlus session) the command DELETE FROM Sysstat - but do not COMMIT.
Go to SQLDeveloper - and (try to) do the following
INSERT INTO Sysstat
SELECT ROUND(TO_DATE (Sysstat_ext.M_Time, 'DD-MM HH24:MI:SS'), 'MI') AS "Measurement Time",
       ROUND(TO_NUMBER(Sysstat_ext.Usr_pct),    0) AS "% Usr",
       <fields deleted>
FROM Sysstat_ext
COMMIT;The SQLDeveloper session completely hangs - forever* (at least 20 mins at this stage).
As I understood matters with Oracle there were three possibilities.
1) PK violation. The SQLDeveloper session "sees" that there are still records in Sysstat (changes
are uncommitted as far as he's concerned), but there is a PK violation in the data to
be inserted anyway, so the SQLDeveloper session should tell the user Sysstat_PK violation.... error...
2) No potential PK violation. The SQLDeveloper session doesn't know whether the SQL*Plus
session will commit its deletions or not, therefore the SQLDeveloper session commits and Oracle keeps track of the
necessary chains of pointers internally and/or when the SQL*Plus session tries to commit, it's accepted or refused
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or
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and informs the user.
Could some kind soul explain to me what, exactly, is going on - and why my reasoning is so obviously erroneous.
I have been looking at Kyte's architecture book, so maybe a concrete example (I've never deadlocked Oracle
before) would help clarify the concepts for me.
Paul...

Paulie wrote:
>
Could some kind soul explain to me what, exactly, is going on - and why my reasoning is so obviously erroneous.
I have been looking at Kyte's architecture book, so maybe a concrete example (I've never deadlocked Oracle
before) would help clarify the concepts for me.I've now read a bit about mutexes in Oracle - not that I understood all of it.
no deadlock is occuring.Well, what else should one call a session that is blocked indefinitely? Is there another
computer science term for this phenomenon?
I suspect a Mutex wait is the cause.OK - so, some sort of device to "regulate concurrent access to a shared resource". That's fine.
The blogs and websites which discuss this seem to be a propeller-head's wet dream with obscure X$_Blah
table configs and Totallyunknown_even_to_Oracle_Support parameters being bandied about like there's
no tomorrow.
What I would like to know is a bit more prosaic (and perhaps a level less technically sophisticated).
Is my reading of Oracle's Locking/Latching/Multi-User behaviour correct in what I wrote originally, i.e.
Scenarios:
1) PK violation. The SQLDeveloper session "sees" that there are still records in Sysstat (deletion
is uncommitted as far as he's concerned), but there is a PK violation in the data to
be inserted anyway, so the SQLDeveloper session should tell the user Sysstat_PK violation.... error...
no change to database - SQLDev user informed
2) No potential PK violation. The SQLDeveloper session doesn't know whether the SQL*Plus
session will commit its deletions or not, therefore the SQLDeveloper session commits and Oracle keeps track of the
necessary chains of pointers internally and/or when the SQL*Plus session tries to commit, it's accepted or refused
depending on whether this will cause other issues (FK violation for example)
or
3) Oracle knows that there's a deadlock and after a certain period (configurable?) rolls back the SQLDeveloper session
and informs the user.
Or am I still competely at sea with what Oracle is about? I was of the understanding that whatever* happened,
you should never have a situation where a session hangs indefinitely, due to Oracle's system
of multi-version concurrency - basically, I'm asking what is going on here and how does it
fit with my current* (and obviously mistaken) understanding of how Oracle works.
Thanks for your input so far.
Paul...A basic truism exist for Oracle.
Readers do not block writers & writers do not block readers!
What you fail to recognize is that your test case has two WRITERS; both are doing DML!
two sessions want to change same resource & to maintain data consistency & integrity
the changes must be serialized. One must complete before the second can proceed.
Oracle utilizes Interested Transaction List (ITL) to maintain block level data consistency.
SELECT DECODE(request,0,'Holder: ','Waiter: ')||sid sess,
id1, id2, lmode, request, type
FROM V$LOCK
WHERE (id1, id2, type) IN
(SELECT id1, id2, type FROM V$LOCK WHERE request>0)
ORDER BY id1, request
/

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Hi Jurgen,
I'm a developper for PAL from Shanghai team.
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http://docs.oracle.com/cd/E12825_01/epm.111/epm_security/frameset.htm?apas02.html
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Edited by: Veerab on Apr 27, 2011 8:22 AM

Hi,
Have you refered [SAP Note 84348 - Oracle deadlocks, ORA-00060 |https://service.sap.com/sap/support/notes/84348]? It contains good detailed description about possible oracle deadlock situations and analysis.
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Thanks

svarma wrote:
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Oracle 8i locking and timeout

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