Table size difference?

Question

we have 2 db's called UT & ST.. with same setup and data also same
running on hp-ux itanium 11.23 with same binary 9.2.0.6
one of schema called arb contain only materialised views in both db's and with same name of db link connect to same remote server in both db's...
in that schema of one table called rate has tablesize as 323 mb and st db, has same table rate has 480mb of tablesize, by querying the bytes of dba segement of table i found the difference.. query has follows
In UT db
select sum(bytes)/1024/1024 from dba_segments where segment_name='RATE'
output
323
In ST db
select sum(bytes)/1024/1024 from dba_segments where segment_name='RATE'
output
480mb
its quite strange, both of table, contain same ddl and same counts of records and initalextent and next extents, all storage parameter are same and same uniform size of 160k tablespace with both db..
ddl table of ut enviornment
SQL> select dbms_metadata.get_ddl('TABLE','RATE','ARB') from dual;
CREATE TABLE "ARB"."RATE"
( "SEQNUM" NUMBER(10,0) NOT NULL ENABLE,---------- ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
STORAGE(INITIAL 163840 NEXT 163840 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
TABLESPACE "AB_DATA"
ddl table of st enviornment
CREATE TABLE "ARB"."RATE"
( "SEQNUM" NUMBER(10,0) NOT NULL ENABLE,---------- ) PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
STORAGE(INITIAL 163840 NEXT 163840 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
TABLESPACE "AB_DATA"..
tablespace of st db
SQL> select dbms_metadata.get_ddl('TABLESPACE','AB_DATA') from dual;
CREATE TABLESPACE "AB_DATA" DATAFILE
'/koala_u11/oradata/ORST31/ab_data01ORST31.dbf' SIZE 1598029824 REUSE
LOGGING ONLINE PERMANENT BLOCKSIZE 8192
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 163840 SEGMENT SPACE MANAGEMENT MANUAL
tablespace of ut db
SQL> select dbms_metadata.get_ddl('TABLESPACE','AB_DATA') from dual;
CREATE TABLESPACE "AB_DATA" DATAFILE
'/koala_u11/oradata/ORDV32/ab_data01ORDV32.dbf' SIZE 1048576000 REUSE
LOGGING ONLINE PERMANENT BLOCKSIZE 8192
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 163840 SEGMENT SPACE MANAGEMENT MANUAL
why table size is difference?

Answer 1

If everything is the same as you stated, i would guess the bigger table might have some free blocks. If you truncate the bigger one and insert /*+ append */ into bigger (select * from smaller) then check the size of bigger table, see what you can find. By the way, dba_segments, or dba_extents only gives the usage to extents level granulity, withing a extent, there are blocks might not be fully occupied. In order to get exact bytes of the space, you 'll need to use dbms_space package.
You may get some idear from the extream example I created below :
SQL>create table big (c char(2000));
Table created.
SQL>select sum(bytes)/1024 kb from user_segments
SQL>where segment_name='BIG';
KB
128               -- my tablespace is LMT uniform sized 128KB
1 row selected.
SQL>begin
SQL> for i in 1..100 loop
SQL> insert into big values ('A');
SQL> end loop;
SQL>end;
SQL>/
PL/SQL procedure successfully completed.
SQL>select sum(bytes)/1024 kb from user_segments
SQL>where segment_name='BIG';
KB
256               -- 2 extents after loading 100 records, 2KB+ each record
1 row selected.
SQL>commit;
Commit complete.
SQL>update big set c='B' where rownum=1;
1 row updated.
SQL>delete big where c='A';
99 rows deleted.          -- remove 99 records at the end of extents
SQL>commit;
Commit complete.
SQL>select sum(bytes)/1024 kb from user_segments
SQL>where segment_name='BIG';
KB
256               -- same 2 extents 256KB since the HWM is not changed after DELETE
1 row selected.
SQL>select count(*) from big;
COUNT(*)
1               -- however, only 1 record occupies 256KB space(lots of free blocks)
1 row selected.
SQL>insert /*+ append */ into big (select 'A' from dba_objects where rownum<=99);
99 rows created.          -- insert 99 records ABOVE HWM by using /*+ append */ hint
SQL>commit;
Commit complete.
SQL>select count(*) from big;
COUNT(*)
100
1 row selected.
S6UJAZ@dor_f501>select sum(bytes)/1024 kb from user_segments
S6UJAZ@dor_f501>where segment_name='BIG';
KB
512               -- same 100 records, same uniformed extent size, same tablespace LMT, same table
                    -- now takes 512 KB space(twice as much as what it took originally)
1 row selected.