RE: RE: Separate Indexes and Data

Jared,  

Any indexes supporting a "In-Today; Gone-Tomorrow" status table will require index rebuilds. Most of them have monotonically increasing numbers which lends itself to a 'holey' index... (I have a bunch of them with Oracle Apps Concurrent Manager and Workflow tables)  

John Kanagaraj
DB Soft Inc
Phone: 408-970-7002 (W)

Disappointment is inevitable, but Discouragement is optional!

• The opinions and facts contained in this message are entirely mine and do not reflect those of my employer or customers **

-----Original Message-----
Sent: Monday, October 13, 2003 11:39 AM
To: Multiple recipients of list ORACLE-L

hmmm... fodder for an article I've been contemplating.

"Indexes: to rebuild or not to rebuild - that is the question"

There's no need to reclaim space, except in special circumstances.

As Kirti pointed out once, a sequentially incrementing numeric key is possibly one of those circumstances.

Not much point in rebuilding indexes in most cases.

If anyone cares to submit test cases for validation of the need of an index rebuild, you may do so here.

Give me some test fodder!

Jared

        JayMiller_at_tdwaterhouse.com
Sent by: ml-errors_at_fatcity.com

 10/13/2003 08:59 AM
 Please respond to ORACLE-L

        
        To:        Multiple recipients of list ORACLE-L
<ORACLE-L_at_fatcity.com> 
        cc:         
        Subject:        RE: RE: Separate Indexes and Data

I assume that what Rachel is referring to is the fact that indexes will generally not release much space when the underlying rows are deleted. They just keep growing, so if you have a large indexed table that frequently deletes and inserts the indexes can grow to fairly ridiculous sizes over a period of time. We just went through the exercise of rebuilding indexes on a db supporting a 3rd party app and reclaimed about 70% of the allocated index space.

Jay Miller
Sr. Oracle DBA
x68355

-----Original Message-----
Sent: Sunday, October 12, 2003 7:39 AM
To: Multiple recipients of list ORACLE-L

Hi Rachael,

You have me a little confused here.

What do you mean by "We over allocate space" ? To the index segments or to the tablespace ?

Why the need to rebuild the indexes ? How are they using more space than required ?

What do you mean that you adjust the pctfree so you can determine "how small you can resize them to" ?

You seem to go to a lot of trouble, I'm just failing to see what it all achieves ???

Cheers

Richard
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, October 01, 2003 4:34 AM

> Nuh uh, not me... I have never used or experimented with
> auto-allocate.
>
> I separate indexes and tables so that I can reclaim space by
> rebuilding the indexes into smaller space.
>
> I've just completed writing the scripts for the following:
>
> we have a data warehouse, partitioned on the biggest table on date by
> month. There are 10 or 11 indexes on this table. We overallocate space
> when we create the new partition for the next month. Data is loaded
> daily. The hosting company has an automated procedure to add space to
> the datafile if the used space percentage is greater than some number
> (we get charged each time they do this, and they never allocate enough
> space so they do it over and over towards the end of the month).
>
> since the indexes are increasing on a daily basis, we overallocate the
> space. The next month, I go out, determine the
> partition/tablespace/datafiles that need to be resized (naming
> standards rule in this case), rebuild the indexes into an interim
> tablespace, rebuild them back to the original one with a smaller
> pctfree and then determine how small I can resize them down to.
>
> If there were table data in these tablespaces, I'd be out of luck on
> trying to reclaim space
>
>
> --- rgaffuri_at_cox.net wrote:
> > the defrag paper was written back in 1998 I believe. Uniform extents
> > were a good solution pre-9i. We use them here on our 8i databases. I
> > stick with an uniform 5m extent size even though I have tables that
> > can fit into 128k extents, but feel that the overall time savings by
> > using 1 extent size makes up for this.
> >
> > unfortunately unlike most systems we cannot break up our tables into
> > different tablespaces. We use transportable tablespaces to batch
> > publish data to data marts. New tablespaces mean additional
> > transportable tablespaces and more places for stuff to go wrong.
> >
> > I saw some posts on dejanews recently from some pretty experienced
> > DBAs stating that there may be 'flaws' in auto-allocate leading to
> > poor extent sizes that leads to fragmentation. I believe Rachel
> > Carmichael made a post on here a few months back with the similiar
> > experience(could be wrong). Due to even the 'small' chance of flaws
> > in auto-allocate, Im thinking of waiting for version 10g before
> > using it. Just to be safe. Not worth risking a defrag on a
> > production system.
> > >
> > > From: "MacGregor, Ian A." <ian_at_SLAC.Stanford.EDU>
> > > Date: 2003/09/30 Tue PM 01:34:28 EDT
> > > To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> > > Subject: RE: Separate Indexes and Data
> > >
> > > I'd be very interested to know how many people have their index
> > tablespaces on a different backup schedule from their data
> > tablespaces. If so how different? What happens when a media
> > failure occurs and you must restore from backup? You would need to
> > have on hand and apply more redo logs to make the database current.
> > >
> > > I understand the argument proffered is separating indexes and data
> > can mean that when physical corruption of the file happens to an
> > index tablespace then all one needs do is to offline, drop, drop and
> > rebuild the index tablespace. I admit I have not tried off-lining
> > the tablespace first, but you cannot normally drop a tablespace
> > which is being used to enforce referential integrity. If off-lining
> > the tablespace first does work, I can see someone trying to do the
> > rebuild with the database available and having duplicate records in
> > the parent tables and records without parents in the child tables.
> > >
> > > On the size of the segments: The paper entitled "How To Start
> > Defragmenting and Start Living" or something like that strongly
> > advocated uniform extent sizes, the suggestion sizes were 128K, 4M,
> > 128M, and 4G as I recall. However the paper
> > > Never mentioned what to do when an object that used to fit nicely
> > into the 128k extent category now more properly belongs to the 4M
> > category. If you move the data, large holes are left in the other
> > tablespace, and while this does not impact Oracle performance, it
> > does mean that your physical backups are larger than necessary. I
> > am in the process of migrating from uniform to autoallocated
> > extents. This means extents of different sizes share the same
> > tablespace. The extent sizes being multiples of each other. This
> > removes the argument about not having indexes and data in the same
> > tablespaces due to their different sizes.
> > >
> > > Ian MacGregor
> > > Stanford Linear Accelerator Center
> > > ian_at_slac.stanford.edu
> > >
> > > -----Original Message-----
> > > Sent: Monday, September 29, 2003 8:10 AM
> > > To: Multiple recipients of list ORACLE-L
> > >
> > >
> > > Thomas,
> > >
> > > It *is* a good idea to separate index data from heap data into
> > different tablespaces. But the reason isn't solely to eliminate I/O
> > competition. Even if I/O competition isn't an issue for you (and the
> > OFA Standard doesn't say that it will be), then it's *still* a good
> > idea to separate your index data from your heap data, for reasons
> > including:
> > >
> > > * Index segments have different backup and recovery requirements
> > than their corresponding heap segments. For example, as Peter
> > mentioned, if you have an index block corruption event, then it's
> > convenient to just offline, kill, and rebuild an index tablespace.
> > If the indexes and data are mixed up in a single tablespace, this is
> > not an option. Another
> > > example: If you construct your backup schedule to make media
> > recovery time a constant, then you probably don't need to back up
> > your indexes on the same schedule as you back up your heaps. But
> > unless they're in different tablespaces, this isn't an option
> > either.
> > >
> > > * Index segments are usually smaller than their corresponding heap
> > segments. Using separate tablespaces allows you to use a smaller
> > extent size to conserve disk storage capacity.
> > >
> > > I don't think I ever wrote that you need to put indexes and their
> > corresponding tables/clusters on separate disks, but you do need to
> > be
> > > *able* to do that if your I/O rates indicate that you should.
> > >
> > > For the original OFA Standard definition, please see section 3 of
> > the document called "The OFA Standard--Oracle for Open Systems," and
> > section 5 of "Configuring Oracle Server for VLDB," both available
> > for free at www.hotsos.com.
> > >
> > >
> > > Cary Millsap
> > > Hotsos Enterprises, Ltd.
> > > http://www.hotsos.com
> > >
> > > Upcoming events:
> > > - Performance Diagnosis 101: 10/28 Phoenix, 11/19 Sydney
> > > - Hotsos Symposium 2004: March 7-10 Dallas
> > > - Visit www.hotsos.com for schedule details...
> > >
> > >
> > > -----Original Message-----
> > > Thomas Day
> > > Sent: Monday, September 29, 2003 9:05 AM
> > > To: Multiple recipients of list ORACLE-L
> > >
> > >
> > > My struggle is not with the directory layout OFA.
> > >
> > > It is with the "mythical" OFA that every DBA that I have talked to
> > knows all about. Where ORACLE says that if you are a good and
> > competent DBA you will separate your table data and your index data
> > into two separate tablespaces so that one disk head can be reading
> > index entries while another disk head is reading the table data.
> > You've never run into that?
> > >
> > >
> > >
> > >
> > >
> > > Tim Gorman <tim
> > >
> > > @sagelogix.com> To: Multiple
> > > recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> >
> > > Sent by: cc:
> > >
> > > ml-errors Subject: Re: BAARF
> > >
> > >
> > >
> > >
> > >
> > > 09/28/2003 09:44
> > >
> > > PM
> > >
> > > Please respond
> > >
> > > to ORACLE-L
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Thomas,
> > >
> > > Please pardon me, but you are off-target in your criticisms of
> > > OFA.
> > >
> > > It has never advocated separating tables from indexes for
> > performance purposes. Ironically, your email starts to touch on the
> > real reason for separating them (i.e. different types of I/O,
> > different recovery requirements, etc). Tables and indexes do belong
> > in different tablespaces, but not for reasons of performance.
> > >
> > > Cary first designed and implemented OFA in the early 90s and
> > formalized it into a paper in 1995. Quite frankly, it is a
> > brilliant set of rules of how Oracle-based systems should be
> > structured, and a breath of fresh air from the simplistic way that
> > Oracle installers laid things out at the time. It took several years
> > for Oracle Development to see the light and become OFA-compliant,
> > and not a moment too soon either. Just imagine if everything were
> > still installed into a single directory tree under ORACLE_HOME? All
> > of things you mention here have nothing to do with OFA.
> > >
> > > Please read the paper.
> > >
> > > Hope this helps...
> > >
> > > -Tim
> > >
> > > P.S. By the way, multiple block sizes are not intended for
> > > performance
> > > optimization; they merely enable transportable
> > > tablespaces
> > between
> > > databases with different block sizes.
> > >
> > >
> > > on 9/25/03 11:04 AM, Thomas Day at tday6_at_csc.com wrote:
> > >
> > > >
> > > > I would love to have a definitive site that I could send all
> > RAID-F
> > > > advocates to where it would be laid out clearly, unambiguously,
> > and
> > > > definitively what storage types should be used for what purpose.
> > > >
> > > > Redo logs on RAID 0 with Oracle duplexing (y/n)?
> >
> === message truncated ===
>
>
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