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Re: Tablespace layout

From: Don Granaman <granaman_at_home.com>
Date: Tue, 28 Aug 2001 23:09:27 -0700
Message-ID: <F001.0037A9CD.20010828231023@fatcity.com>

There is no advantage at all in making extent sizes a function of db_block_buffers.

I agree, to a certain extent (no pun intended), with the idea of using
"dedicated" tablespaces. I prefer to use dedicated tablespaces for all
"significantly large" tables, where the value for "significantly large" is
subjective. For example, in a very critical 200 GB OLTP database, it might mean dedicated tablespaces for tables of 200 MB or larger, a few tablespaces - with uniform extent sizes - for smaller tables, and dedicated tablespaces - also with uniform extent sizes - for indexes on larger tables. For example, ACCT_DATA, ACCT_INDX, CUST_DATA, CUST_INDX, ORDR_DATA, ORDR_INDX, STAT_DATA, STAT_INDX, etc. Another consideration is in how the contents of the tablespace are used. STAT_DATA, for example, might be reserved for largely static tables. There might be another tablespace for similarly sized tables that are very volatile.

In general, my main considerations are:

Object size

    uniform extents - ironclad rule for everything except SYSTEM, in all but most rare circumstances

    only a few different extent sizes for all app data and indexes in the entire database

    ignore the "multiple extents kills performance" myth (but keep it
"reasonable"!)

Volatility

    read-only data?
    objects continually dropped/truncated and recreated/reloaded     intensely transactional?
     etc...

I/O distribution

    a single non-dedicated tablespace should not contain objects likely to be in contention

    separate indexes and data (I/O effect is debatable, but index rebuilds, etc. favor)

    tablespace design so as to support reasonably even I/O distribution across disks/stripe sets

    ability to (relatively) easily move datafiles to rebalance I/O

Recoverability

    Preference for many tablespaces over very large multi-table tablespaces     Preference for more smaller datafiles over very large datafiles (files > 2 GB are very rarely needed)

Partitioning

    For large partitioned objects - a tablespace for each partition     Rolling temporal partitions - as above. Age off or move data by partition exchange

Transportable tablespaces

    What, if anything , needs to be moved? (e.g to a warehouse staging area)     At what frequency / data volume?

Parallel server

    Access patterns, PCM lock allocation (pre-9i at least), etc.

This works best with something like only three or four different extent sizes for everything - except perhaps rollback, system, and temp, and perhaps only three or four different datafile sizes for everything except perhaps control files and redo logs.

The above is an "off the top of the head" list. I don't pretend that it is comprehensive. However, it might generate some interesting discussion. It seems that space management is sometimes almost a religious topic. I converted to the "uniform extents" philosophy early - about 1990 - and confess to being an evangelist.

-Don Granaman
[certifiable OraSaurus]

I agree completely with Lisa. Several years ago I had a chance to talk with an Oracle tester in IBM's benchmark lab. They had a one table/one tablespace/one datafile layout, mostly for recoverability. Once you document it fully (and name it logically) administration is not that difficult.

For those of you who know Oracle internals, is there any advantage in making the uniform extents a multiple of the db_block_buffers area in the SQA? Or is that just a feeling left over from when I had to align strings on full-words while programming assembler?

                    "Koivu, Lisa"
                    <lisa.koivu_at_efair        To:     Multiple recipients of
list ORACLE-L
                    field.com>               <ORACLE-L_at_fatcity.com>
                    Sent by:                 cc:
                    root_at_fatcity.com         Subject:     RE: Tablespace
layout
                    08/28/2001 05:07
                    PM
                    Please respond to
                    ORACLE-L








Well Satar you didn't even read Cherie's email.

Way back before I took that db to the tablespace layout you refer to (straight out of HOw to Stop Defragmenting and Start Living white paper) I had created a separate tablespace for each partition. It was an awful pain back then and the number of tablespaces I had was ridiculous. I can see your point with mttr and keeping your tablespaces fairly small in comparison to what it's become. I guess it's a tradeoff with pros and cons either way.

However, I suggest you take that paper (above) and throw it their faces. I disagree about different sized extents in the same tablespace vehemently. I think they should be uniform, period, for the same reason you state - if disk is so precious, then use it wisely !! Plus, when your partition starts looking for another 100MB extent, you are out of luck.

What's your feeling on partitioning? I think if you are dropping data monthly, use partitions wherever you can. That way you are more assured of reusing your disk - however, then you are looking at a different tablespace per partition.

I believe at one point I had 2-3 partitions in each tablespace, rotating them (part1 in ts1, part2 in ts2, part3 in ts1, part4 in ts2, etc.) Maybe that will provide the compromise in functionality, disk space management and recoverability you seek.

I do know your pain. Good Luck.

Lisa Koivu
Certified Monkey and DBA
Ft. Lauderdale, FL, USA

   -----Original Message-----
   From: Satar Naghshineh [SMTP:Satar.Naghshineh_at_irvine.mellesgriot.com]    Sent: Tuesday, August 28, 2001 4:30 PM    To: Multiple recipients of list ORACLE-L    Subject: RE: Tablespace layout

   Hi Cherie,

   Just shove all your data on a RAID 5 (great for data Warehouses) and    forget about it. If that is not possible, then stick with what your DBA    team has stated about everything being ok as long as the extents are    multiples of one another.

   Regards,
   Satar Naghshineh

   -----Original Message-----
   From: Cherie_Machler_at_gelco.com [SMTP:Cherie_Machler_at_gelco.com]    Sent: Tuesday, August 28, 2001 7:27 PM    To: Multiple recipients of list ORACLE-L    Subject: Tablespace layout

   I've been thinking a lot about our tablespace layout for our    data warehouse. Our warehouse is approaching 200Gig    and is almost out of space on disk. I'm getting another 75 Gig    this weekend and am trying to plan the best use for that 75Gig.

   Our current data tablespace layout is that we have two tablespaces    for small, medium, and large data tables and the same for indexes.    So it's something like this:

   SM_DATA01
   SM_DATA02
   MED_DATA01
   MED_DATA02

   LG_DATA01
   LG_DATA02
   SM_IDX01
   SM_IDX02

   MED_IDX01
   MED_IDX02
   LG_IDX01
   LG_IDX02    I think that theoretically, all of the tables in each of the tablespaces    were supposed to have the same sized extents when they were    originally created. However, over time, there are multiple sizes    of extents in the large and medium tablespaces. Even though we    show significant free space, it is fragmented and coalescing can    not put together enough contiguous space to reuse a lot of the available    space.

   Our largest tables are partitioned. However the partitions are not    split
   out into separate tablespaces but go into the same medium and large    tablespaces as non-partitioned tables. Theoretically, I suppose that    this
   is not a problem if, when partitions are dropped every month, the    resulting
   space is reused 100%. I'm not sure if it is.

   Here is my question. My DBA team members feel that it's fine to have    tables with a variety of extent sizes in the same tablespace as long as    they are all multiples of each other (50, 100, 400, 2000, etc.). My    concern
   is that this setup is fine when the smaller tables need to extend but    when
   the larger tables need to extend, they can't pull together enough    contiguous
   space and I keep having to add more. I'd prefer to have only one size    of
   extent in each tablespace and keep it very pure that way. Then I know    every single extent can be reused. So I am considering increasing the    number of tablespaces so we have something more like this:

   1kdata
   10kdata
   100kdata
   1mdata
   10mdata
   100mdata
   1000mdata
   1kidx
   10kidx
   100kidx
   1midx
   10midx
   100midx
   1000midx

   I would also probably split them out into at least two tablespaces for    each
   level.
   Maybe not for the smaller sizes, but for the larger sizes.

   I have several issues I'm trying to keep in mind. One is the ease of    maintenance
   for initial creation and ongoing upkeep. I don't want to have too many    tablespaces
   if I don't need to. Another issue is mean time to recover. If we    lose a
   single tablespace,
   I'd prefer to have to recover fewer files. The maximum file size we are    using is 2Gig.
   We need to keep our recovery time under four hours total.

   Probably the biggest issue I'm facing now is the sheer size of the large    tablespaces.
   They are so big and bulky that it's almost impossible to reorg them or    even
   just
   clean them up. I think that if I had more smaller tablespaces, I would    have more
   options. This database is still at 8.0.4 and it's going to be a while    before it can be
   upgraded so that limits my options for reorging as well. All cleanup    has
   to be done
   in a series short Sunday windows. I don't have the luxury of a tool for    doing this
   reorg so have to do it manually.

   Another issue is partitions. We are dropping the old partitions on the    main fact
   table once a month. We are not currently planning on dropping any of    the
   other partitions.
   The tables have a variety of partition names and schemes. Some are    partitioned yearly,
   monthly, quarterly, half-yearly. There is no consistency. I'm    debating
   whether I should
   split each partition out into it's own tablespace. That would be    almost a
   hundred tablespaces.
   Or just the table that we're dropping partitions on monthly. That    would
   be about 50 tablespaces.
   Or should I just leave them all in the same tablespaces as    non-partitioned
   tables?

   We are using Sun Solaris 2.6 on an E10K. We have EMC disk and Veritas    file manager.
   Using version 8.0.4 of Oracle, as I said. Using RMAN and Veritas for    backups.

   Any feedback, ideas, suggestions, things to watch out for, think about,    etc. would be greatly
   appreciated. This is going to take a lot of time and effort to do and    I
   don't want to get all the
   work done and find out it doesn't work as well as I hoped and have to    redo
   everything.

   Thanks for your time,

   Cherie Machler
   Oracle DBA
   Gelco Information Network

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   Author:
   INET: Cherie_Machler_at_gelco.com

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Received on Wed Aug 29 2001 - 01:09:27 CDT

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