Huge fragmentation/inflation in the table

Question

Hi,
I have an application that does insert of data from flat files to the tables every two week. Each time while loading data, the application deletes all the relevant data that is being reloaded (I mean the table is not entirely truncated or all rows are not deleted but a portion of it - identified by values of two columns like customer_id and data_category_type -all data of given customer_id and data_category_type are deleted every fortnight.)
Now the strange thing I see is that my table is getting HEAVILY inflated! The average row length is just 73 bytes for each rows, as of now this table has just 1316 rows and the number of blocks for this table are 2638!! Note that the table has undergone several huge inserts and deletes - several thousand rows over several months but as of now it has just this much data.
select num_rows,avg_row_len,blocks from
user_tables where table_name='MASS_DML_TABLE';
  NUM_ROWS AVG_ROW_LEN     BLOCKS
      1316          73       2638
(Note: i just made up a different table name as we have to give only generic info not actual schema name, but all other statistics are absolutely actual -not made up). What can cause this - I can confirm that we do not user /* +APPEND */ hint - the inserts are simple inserts...so when the rows are deleted shouldn't oracle be able to use to available space? Why is this extreme inflated space situation got created , what coudl be the cause of it?
I will be thankful for the help!
Regards

Answer 1

Mark D Powell wrote:
Space freed from deleted rows should be reusuable providing the session that performs the delete processing commits prior to performing the insert operation. The presence of Long or Long Raw columsn in the table would encourgage Oracle to send the inserts into new blocks.Mark,
While this is true for an index (or an IOT), I don't think this is applicable to heap tables.
My test case below. Table T1 has been created in an ASSM tablespace with 8KB block size.
SQL> select * from v$version ;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE     10.2.0.1.0     Production
TNS for Linux: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
SQL> create table t1 (tid number, padding char(200) default 'x');
Table created.
SQL> exec show_space('T1') ;
Unformatted Blocks .....................            0
FS1 Blocks (0-25)  .....................            0
FS2 Blocks (25-50) .....................            0
FS3 Blocks (50-75) .....................            0
FS4 Blocks (75-100).....................            0
Full Blocks        .....................            0
Total Blocks............................            8
Total Bytes.............................       65,536
Total MBytes............................            0
Unused Blocks...........................            5
Unused Bytes............................       40,960
Last Used Ext FileId....................            6
Last Used Ext BlockId...................        1,057
Last Used Block.........................            3
PL/SQL procedure successfully completed.
SQL> begin
  2    for i in 1..1000 loop
  3      delete from t1 where tid = (i-1);
  4      insert into t1(tid) values (i) ;
  5    end loop;
  6    commit ;
  7  end;
  8  /
PL/SQL procedure successfully completed.
SQL> select count(*) from t1 ;
  COUNT(*)
      1
SQL> exec show_space('T1') ;
Unformatted Blocks .....................            0
FS1 Blocks (0-25)  .....................            0
FS2 Blocks (25-50) .....................            0
FS3 Blocks (50-75) .....................            1
FS4 Blocks (75-100).....................            4
Full Blocks        .....................            0
Total Blocks............................            8
Total Bytes.............................       65,536
Total MBytes............................            0
Unused Blocks...........................            0
Unused Bytes............................            0
Last Used Ext FileId....................            6
Last Used Ext BlockId...................        1,057
Last Used Block.........................            8
PL/SQL procedure successfully completed.
SQL> truncate table t1 ;
Table truncated.
SQL> begin
  2    for i in 1..1000 loop
  3      delete from t1 where tid = (i-1);
  4      commit;
  5      insert into t1(tid) values (i) ;
  6      commit;
  7    end loop;
  8  end;
  9  /
PL/SQL procedure successfully completed.
SQL> exec show_space('T1') ;
Unformatted Blocks .....................            0
FS1 Blocks (0-25)  .....................            0
FS2 Blocks (25-50) .....................            0
FS3 Blocks (50-75) .....................            0
FS4 Blocks (75-100).....................            5
Full Blocks        .....................            0
Total Blocks............................            8
Total Bytes.............................       65,536
Total MBytes............................            0
Unused Blocks...........................            0
Unused Bytes............................            0
Last Used Ext FileId....................            6
Last Used Ext BlockId...................        1,057
Last Used Block.........................            8
PL/SQL procedure successfully completed.
SQL> select count(*) from t1 ;
  COUNT(*)
      1Edited by: user503699 on Oct 14, 2010 12:40 AM - Just realised that my test was flawed. So corrected it but the results still show that space is reused