Index size keep growing while table size unchanged

Question

Hi Guys,
I've got some simple and standard b-tree indexes that keep on acquiring new extents (e.g. 4MB per week) while the base table size kept unchanged for years.
The base tables are some working tables with DML operation and nearly same number of records daily.
I've analysed the schema in the test environment.
Those indexes do not fulfil the criteria for rebuild as follows,
- deleted entries represent 20% or more of the current entries
- the index depth is more then 4 levels
May I know what cause the index size keep growing and will the size of the index reduced after rebuild?
Grateful if someone can give me some advice.
Thanks a lot.
Best regards,
Timmy

Answer 1

Please read the documentation. COALESCE is available in 9.2.
Here is a demo for coalesce in 10G.
YAS@10G>truncate table t;
Table truncated.
YAS@10G>select segment_name,bytes from user_segments where segment_name in ('T','TIND');
SEGMENT_NAME              BYTES
T                         65536
TIND                      65536
YAS@10G>insert into t select level from dual connect by level<=10000;
10000 rows created.
YAS@10G>commit;
Commit complete.
YAS@10G>
YAS@10G>select segment_name,bytes from user_segments where segment_name in ('T','TIND');
SEGMENT_NAME              BYTES
T                        196608
TIND                     196608We have 10,000 rows now. Let's delete half of them and insert another 5,000 rows with higher keys.
YAS@10G>delete from t where mod(id,2)=0;
5000 rows deleted.
YAS@10G>commit;
Commit complete.
YAS@10G>insert into t select level+10000 from dual connect by level<=5000;
5000 rows created.
YAS@10G>commit;
Commit complete.
YAS@10G>select segment_name,bytes from user_segments where segment_name in ('T','TIND');
SEGMENT_NAME              BYTES
T                        196608
TIND                     327680Table size is the same but the index size got bigger.
YAS@10G>exec show_space('TIND',user,'INDEX');
Unformatted Blocks .....................               0
FS1 Blocks (0-25)  .....................               0
FS2 Blocks (25-50) .....................               6
FS3 Blocks (50-75) .....................               0
FS4 Blocks (75-100).....................               0
Full Blocks        .....................              29
Total Blocks............................              40
Total Bytes.............................         327,680
Total MBytes............................               0
Unused Blocks...........................               0
Unused Bytes............................               0
Last Used Ext FileId....................               4
Last Used Ext BlockId...................          37,001
Last Used Block.........................               8
PL/SQL procedure successfully completed.We have 29 full blocks. Let's coalesce.
YAS@10G>alter index tind coalesce;
Index altered.
YAS@10G>select segment_name,bytes from user_segments where segment_name in ('T','TIND');
SEGMENT_NAME              BYTES
T                        196608
TIND                     327680
YAS@10G>exec show_space('TIND',user,'INDEX');
Unformatted Blocks .....................               0
FS1 Blocks (0-25)  .....................               0
FS2 Blocks (25-50) .....................              13
FS3 Blocks (50-75) .....................               0
FS4 Blocks (75-100).....................               0
Full Blocks        .....................              22
Total Blocks............................              40
Total Bytes.............................         327,680
Total MBytes............................               0
Unused Blocks...........................               0
Unused Bytes............................               0
Last Used Ext FileId....................               4
Last Used Ext BlockId...................          37,001
Last Used Block.........................               8
PL/SQL procedure successfully completed.The index size is still the same but now we have 22 full and 13 empty blocks.
Insert another 5000 rows with higher key values.
YAS@10G>insert into t select level+15000 from dual connect by level<=5000;
5000 rows created.
YAS@10G>commit;
Commit complete.
YAS@10G>select segment_name,bytes from user_segments where segment_name in ('T','TIND');
SEGMENT_NAME              BYTES
T                        262144
TIND                     327680Now the index did not get bigger because it could use the free blocks for the new rows.