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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Automatic Segment Space Management
Gee, John, I was not aware of this underscore parameter. In my 9.2 database
it's 6, just as yours.
I did my test using upto three concurrent tranactions; guess I'll need to test with 7 or more. However, even if 7 concurrent transactions update the block's rows, and the limit is 6, then the waits should be based in ITL (Interested Trasnaction List) Waits, not BBW. since this is not due to a session not being able to get a particular buffer to the SGA, rather the lack of resources to get the CR copy of a buffer.
Has anyone done this test? I'll certainly take it up later to build up on my upcoming article on ITL Waits.
Regards,
Arup
> Arup,
>
> Just picking up the thread on the BBWs. (Btw, I asked this question in
this
> list - never got an answer!) The following undocumented parameter limits
the
> numbe of CR copies in the Block buffers.
>
> Name Value
> --------------------------------------------- ----------------------------
--Received on Wed Feb 19 2003 - 16:03:29 CST
> Description
> --------------------------------------------------------------------------
--
> ---
> _db_block_max_cr_dba 6
> Maximum Allowed Number of CR buffers per dba
>
> What if there are more than 6 concurrent update requests for the same
block.
> Would that not result in BBW?
>
> John Kanagaraj
> Oracle Applications DBA
> DBSoft Inc
> (W): 408-970-7002
>
> Disappointment is inevitable, but Discouragement is optional!
>
> ** The opinions and statements above are entirely my own and not those of
my
> employer or clients **
>
>
> > -----Original Message-----
> > From: Arup Nanda [mailto:orarup_at_hotmail.com]
> > Sent: Wednesday, February 19, 2003 8:24 AM
> > To: Multiple recipients of list ORACLE-L
> > Subject: Re: Automatic Segment Space Management
> >
> >
> > Jay,
> >
> > I have been using ASSM for last five months in our Datawarehouse
> > environment. Haven't had a chance to play with the OLTP side, yet.
> >
> > Inserts are way faster as compared to system managed extent
> > allocation. I
> > read Don's article on DBAZINE. However, I would like to add
> > one caveat here:
> > ASSM does not *eliminate* buffer busy waits as the article claims; it
> > *reduces* them. BBW occur due to concurrent access to a
> > buffer by more than
> > one session. This will be the case regardless of number of
> > freelists. While
> > ASSM eliminates the freelist contention - thereby reducing
> > BBW in inserts -
> > it does not reduce the likelihood that more than one sessions
> > will try to
> > get the same block to the buffer cache simulataneously.
> >
> > Table drops appear a little slower in ASSM; but that could be
> > wrong - I
> > never timed dropping a table in the system managed mode.
> >
> > HTH.
> >
> > Arup Nanda
> >
> >
> > ----- Original Message -----
> > To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> > Sent: Wednesday, February 19, 2003 9:33 AM
> >
> >
> > > I'm continuing to introduce myself to 9i. I've been reading about
> > Automatic Segment Space Management, and I just wondered if
> > anybody had any
> > positive/negative experiences with it. I got some good info at:
> > >
> > > http://www.dbazine.com/burleson11.html
> > >
> > >
> > > Thank you,
> > >
> > >
> > > Jay Hostetter
> > > Oracle DBA
> > > D. & E. Communications
> > > Ephrata, PA USA
> > >
> > >
> > >
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Arup Nanda INET: orarup_at_hotmail.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (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).
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