OLTP behavior in Oracle 11g R2

Question

Hi everyone.
Someone could please explain this behavior.
I've three tables, one in OLTP compression, other in basic compression and other without compression.
When I inserted lines on OLTP table, these lines are not compressed.
Only after do a "move" the segment shrinks.
My test case (Oracle 11.2.0.3.8):
create table a_normal
as
select rownum id, a.*
from all_objects a
create table a_compress
as
select rownum id, a.*
from all_objects a
create table a_comp_oltp
as
select rownum id, a.*
from all_objects a
SQL> alter table a_compress move compress;
Table altered.
SQL> alter table a_comp_oltp compress for oltp;
Table altered.
SQL> select table_name, compression, compress_for, pct_free from dba_tables where table_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
TABLE_NAME                     COMPRESS COMPRESS_FOR   PCT_FREE
A_NORMAL                       DISABLED                      10
A_COMP_OLTP                    ENABLED  OLTP                 10
A_COMPRESS                     ENABLED  BASIC                 0
SQL> select segment_name, bytes/1024 from dba_segments where segment_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
SEGMENT_NAME                                                                      BYTES/1024
A_COMP_OLTP                                                                            10240
A_COMPRESS                                                                              3072
A_NORMAL                                                                               10240As you can see here, even after the move compress for oltp, the space used still the same.
Now, after the "move", our space shrinks.
SQL> alter table a_comp_oltp move;
Table altered.
SQL> select segment_name, bytes/1024 from dba_segments where segment_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
SEGMENT_NAME                                                                      BYTES/1024
A_COMP_OLTP                                                                             4096
A_COMPRESS                                                                              3072
A_NORMAL                                                                               10240And, after that, I inserted 4 million rows without append and more 4 million with append, both are not compressed until before I did a "move".
SQL> @ins_a_comp_oltp
Enter value for 1: 4000000
old   3: l_rows number := &1;
new   3: l_rows number := 4000000;
Enter value for 1: 4000000
old   9: where rownum <= &1;
new   9: where rownum <= 4000000;
PL/SQL procedure successfully completed.
SQL> select segment_name, bytes/1024 from dba_segments where segment_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
SEGMENT_NAME                                                                      BYTES/1024
A_COMP_OLTP                                                                           493568
A_COMPRESS                                                                              3072
A_NORMAL                                                                               10240
SQL> alter table A_COMP_OLTP move;
Table altered.
SQL>  select segment_name, bytes/1024 from dba_segments where segment_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
SEGMENT_NAME                                                                      BYTES/1024
A_COMP_OLTP                                                                           188416
A_COMPRESS                                                                              3072
A_NORMAL                                                                              499712
SQL> @ins_a_comp_oltp_append
Enter value for 1: 4000000
old   3: l_rows number := &1;
new   3: l_rows number := 4000000;
Enter value for 1: 4000000
old   9: where rownum <= &1;
new   9: where rownum <= 4000000;
PL/SQL procedure successfully completed.
SQL>  select segment_name, bytes/1024 from dba_segments where segment_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
SEGMENT_NAME                                                                      BYTES/1024
A_COMP_OLTP                                                                           665600
A_COMPRESS                                                                              3072
A_NORMAL                                                                              499712
SQL> alter table A_COMP_OLTP move;
Table altered.
SQL> select segment_name, bytes/1024 from dba_segments where segment_name in ('A_COMPRESS','A_COMP_OLTP','A_NORMAL');
SEGMENT_NAME                                                                      BYTES/1024
A_COMP_OLTP                                                                           360448
A_COMPRESS                                                                              3072
A_NORMAL                                                                              499712When I read the documentation, it says "When a block reaches the PCTFREE value, it will be compressed, if the compression make the block leaves the PCTFREE threshold it will can accept more lines, and do the compression again"
But here, even with a 4 million insert, the table is not compressed, neither with append (direct-path), why?
Thanks and regards,
Felipe.
Edited by: Felipe Romeu on 09/10/2012 14:43

Answer 1

It works for me:orcl> create table nocomp (c1 varchar2(10));
Table created.
orcl> create table oltpcomp(c1 varchar2(10)) compress for oltp;
Table created.
orcl> insert into nocomp select 'aaaaaaaaaa' from dual connect by level < 1000000;
999999 rows created.
orcl> insert into oltpcomp select 'aaaaaaaaaa' from dual connect by level < 1000000;
999999 rows created.
orcl> select segment_name,bytes from user_segments where segment_name like '%COMP';
SEGMENT_NAME                                                                           BYTES
NOCOMP                                                                              18874368
OLTPCOMP                                                                            13631488
orcl> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for 32-bit Windows: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
orcl>