Calculate free space without reorg

Question

Hi DB-Gurus,
we  are currently on AIX and Oracle 9.2.0.6.0. The SAP System is BankAnalyzer, which is an add-on to a BIW (3.5). Data is loaded into the system via STS, a tool from a third party vendor. All relevant tables (BankAnalyzer and STS) are in one tablespace, the size of the tablespace is about 1 TB, of which STS-tables occupy about 400 GB. STS produces a lot of redundant overhead which we now want to archive and delete on a regular basis.
<b>Without</b> a DB-reorg, is there a way to tell how much space is currently free in the DB, and how much space ist occupied? As I understand, DB02 will keep showing the same figures until a reorg is done, even though we have deleted 200 GB from the tables. We need a way to tell the current free space in order to control DB-load and to calculate future DB costs.
We are using database managed tablespaces. If we can't reorg the whole tablespace or DB, will fragmentation over time (archive & delete old STS-data every 3 months and load new data on a daily basis) reduce performance, even though we reorg the index tables?
If we could identify the tables affected from the regular delete and update processes, is there a way to reorg just these tables? Would this be an advisable way to reduce DB-maintenance and increase DB-performence?
Thanks for your valued input & kind regards,
Mark
PS: yes, we are planing an upgrade to 10.2 sometime soon.

Answer 1

Hello Mark,
at first:
<b>>> Since I am not deep into the DB stuff (yet )</b>
That's no problem man ... nobody can know everthing...but i would recommend some extern support, if you don't have the know-how in-house. This topic is pretty deep on database level to make any suggestions or definitive statements...
But now lets start with your questions.
<b>>> STS produces a lot of redundant overhead which we now want to archive and delete on a regular basis.</b>
That's the first good idea
<b>>> Without a DB-reorg, is there a way to tell how much space is currently free in the DB, and how much space ist occupied?</b>
I don't know any SAP possibility to show this (because i don't use man SAP features for analyzing problems / reorgs,etc..), but i can show you some possibilites on database level.
At first some helpful views/tables:
http://download.oracle.com/docs/cd/B10501_01/server.920/a96536/ch2451.htm#1317269
INDEX_STATS - You have to analyze the index first with an ANALYZE INDEX and then you can query the view index_stats in the same session (that's important!). The columns DEL_LF_ROWS, USED_SPACE, PCT_USED are very interesting in your case.
The problem with INDEX_STATS is that you will lock the segment with the ANALYZE command.
http://download.oracle.com/docs/cd/B10501_01/server.920/a96536/ch2152.htm#1303953
ALL_TABLES - This values are populated if you collect statistics for the table, but the values are not as clear as the index ones. The column EMPTY_BLOCKS does not count the empty blocks.. it only counts the blocks that are not formated yet. The column AVG_SPACE is more interesting but you have to set it in the context of some other values.. its really difficult to explain this over the internet without any table values.
<b>>> We are using database managed tablespaces. If we can't reorg the whole tablespace or DB, will fragmentation over time (archive & delete old STS-data every 3 months and load new data on a daily basis) reduce performance, even though we reorg the index tables? </b>
I don't know what you mean with database managed tablespaces. Do you mean data dictionary managed ones or do you mean locally managed ones? But this does not have any affects on the block filling logic (only on extend logic is affected by that)... the block filling logic only depends on automatic segment space mangement or not. You can not make any over-all statement if the performance would be better or not. It depends on so many factors like execution plans (access pathes), reused blocks, etc... Normally the "freed" space is reused, but the performance can be as bad as before if the same blocks are touched (for example index range scans, full table scans, and so on...)
<b>>> If we could identify the tables affected from the regular delete and update processes, is there a way to reorg just these tables? Would this be an advisable way to reduce DB-maintenance and increase DB-performence?</b>
http://download.oracle.com/docs/cd/B10501_01/server.920/a96536/ch2146.htm#1303064
You could identify these ones if you activate the monitoring attribute on the tables and after that you can query the view ALL_TAB_MODIFICATIONS. The data which is populated in that view are the counters since the last collected statistics on the table.
The same as above you can not make any over-all statement if it is good or bad... it depends on so many factors if it will increase the db performance. You can reorg single tables.
I hope it helps a little bit, but if you don't have any experience/know-how on oracle .. it will be really difficult to do any further analysis on that topic.
Regards
Stefan