Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Mailing Lists -> Oracle-L -> RE: How much overhead for datafile headers?

RE: How much overhead for datafile headers?

From: Norwood Bradly A <Bradley.A.Norwood_at_M1.IRSCOUNSEL.TREAS.GOV>
Date: Thu, 25 May 2000 12:43:19 -0400
Message-Id: <10508.106726@fatcity.com> 





If OPS, then do you not need to place control files as well as redo log
files on raw partitions in addition


to the datafiles???



-----Original Message-----



From: Steve Adams [mailto:steve.adams_at_ixora.com.au]
Sent: Thursday, May 25, 2000 7:42 AM


To: Multiple recipients of list ORACLE-L
Subject: RE: How much overhead for datafile headers?




Hi Steve,



When creating a datafile on raw, you need to allow both for the datafile 
header, and the logical volume control block. The size of the former is 
always exactly one Oracle block. The size of the latter depends on your 
platform, and LV manager. My web tip on "Planning Datafiles" suggests 128K 
as big enough if you don't know better. However, Jonathan Lewis and other 
recommend 1M.



I cannot comment on your database corruption experiment. There are too many 
possible "explanations".



Regards,


Steve Adams

http://www.ixora.com.au/
http://www.oreilly.com/catalog/orinternals/
http://www.christianity.net.au/




-----Original Message-----

From:	Steve.Gough_at_gocorp.com.au [SMTP:Steve.Gough_at_gocorp.com.au]
Sent:	Thursday, May 25, 2000 3:23 PM
To:	Multiple recipients of list ORACLE-L
Subject:	RE: How much overhead for datafile headers?






Hi Steve



I've been told to add an extra 1M when creating datafiles on raw devices.
is this too much overhead ?



During testing i've "dd" to a raw device datafile file in the hope of
corrupting it.  I had to "dd" about 4 -  5Mb before the DB wouldn't
function. I assumed it was overwritting a very large header on the data
file, can you shed a some light on this ?



Thanks


Steve Gough



 
   

                    Steve Adams 
                    <steve.adams_at_ixo        To:     Multiple recipients of 
list ORACLE-L
                    ra.com.au>              <ORACLE-L_at_fatcity.com> 
                    Sent by:                cc: 
                    root_at_fatcity.com        Subject:     RE: How much 


overhead for datafile headers?
 
   
 
   

                    25/05/00 11:54 
                    Please respond 
                    to ORACLE-L 
 
   
 
   







Hi Steve,



This is not a Veritas issue.


Your datafile header is just one block.


It is the bitmap for local space management that has messed you up.
The bitmap is always 64K, regardless of the database block size.
So, for locally managed tablespaces you always need to allow
64K more for "headers" than you might otherwise have done.



Regards,


Steve Adams

http://www.ixora.com.au/
http://www.oreilly.com/catalog/orinternals/
http://www.christianity.net.au/




-----Original Message-----

Sent:           Thursday, May 25, 2000 6:06 AM
To:        Multiple recipients of list ORACLE-L





Is there a way to determine how much overhead is being used for a datafile
header? From an X$ table?



Here's what I used to "know:" 1) for file systems you need to allocate one
database block for datafile overhead; 2) for raw the overhead is two
db_blocks. 3) Other considerations for volume managers...



Here's the story...


I had a datafile sized to 1GB + 2 db_blocks (16KB each) with the idea that
it could contain 8 equally sized extents of 128MB in a locally managed
tablespace. Then I "discovered" that the actual size of the datafile
overhead was 4 db_blocks so there wasn't any room for the 8th extent.
:-(The first extent begins at block 5.) The DBA_FREE_SPACE view does not
even list the tablespace, meaning it is full even though there is 131,040KB
of unused space in the datafile. What a waste! Now I have a slew of
datafiles to extend by 64KB.



This was on a Veritas volume which probably means that the overhead for
datafiles on Veritas is 4 db_blocks. The overhead on our non-Veritas files
is only 1 db_block as expected. Supposedly you should be able to find this
out from the platform-specific documentation but I didn't find anything in
the Oracle or Veritas manuals which addresses datafile overhead
requirements.




Here's what the Concepts manual says:




"Oracle creates a datafile for a tablespace by allocating the specified
amount of disk space plus the overhead required for the file header...



Additional Information: For information on the amount of space
required for the file header of datafiles on your operating system,
see your Oracle operating system specific documentation."




Anyone have an idea where to find this info?




Steve Orr



--



Author: Steve Orr


  INET: sorr_at_arzoo.com


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: 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).


--



Author: Steve Adams


  INET: steve.adams_at_ixora.com.au


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: 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).












The information contained in this transmission or any part of it is 
intended only for


the named recipient.  This information is confidential and no part of the 
information


shall be disclosed, copied, redirected or otherwise distributed without the 
express


permission of the sender.  Should this message be received in error by 
anyone other


than the named recipient or any employee or agent of the named recipient, 
or if the


transmission is incomplete, corrupted or includes a mistaken document 
please immediately


delete the transmission and its contents and promptly notify the sender by 
return email


or by telephone on (07) 5579-2800.  Any personal views and opinions of the 
sender expressed


in this transmission are those of the sender and shall not be taken to be 
endorsed nor


conveyed by GOCORP Limited.  While all care and appropriate security 
measures have been


implemented, GOCORP Limited does not accept responsibility for any virus or 
other corruption


of data that may occur as a result of this transmission.






--



Author:


  INET: Steve.Gough_at_gocorp.com.au


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: 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).


-- 



Author: Steve Adams


  INET: steve.adams_at_ixora.com.au


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: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
Received on Thu May 25 2000 - 11:43:19 CDT












Original text of this message













  HOME |
  ASK QUESTION |
  ADD INFO |
  SEARCH |
  E-MAIL US