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28 February, 2016

Compression -- 1b : (more on) BASIC Table Compression

In the previous blog, I demonstrated creating an empty table with BASIC Compression and then populating it.

What if you have a pre-existing table with data that you want to compress ?

Here I start with a table that already has rows but doesn't have compression configured.

PDB1@ORCL> select tablespace_name, segment_type, bytes/1048576
  2  from user_segments
  3  where segment_name = 'REGULAR_1';

TABLESPACE_NAME         SEGMENT_TYPE   BYTES/1048576
------------------------------ ------------------ -------------
HEMANT          TABLE        49

PDB1@ORCL> select pct_free, blocks, num_rows, blocks*8192/1048576
  2  from user_tables
  3  where table_name = 'REGULAR_1';

  PCT_FREE     BLOCKS NUM_ROWS BLOCKS*8192/1048576
---------- ---------- ---------- -------------------
 10  6224   364496       48.625

PDB1@ORCL>


I then proceed to rebuild it as a COMPRESSed table.

PDB1@ORCL> alter table regular_1 move compress;

Table altered.

PDB1@ORCL> exec dbms_stats.gather_table_stats('','REGULAR_1');

PL/SQL procedure successfully completed.

PDB1@ORCL> select tablespace_name, segment_type, bytes/1048576
  2  from user_segments
  3  where segment_name = 'REGULAR_1';

TABLESPACE_NAME         SEGMENT_TYPE   BYTES/1048576
------------------------------ ------------------ -------------
HEMANT          TABLE        12

PDB1@ORCL> select pct_free, blocks, num_rows, blocks*8192/1048576
  2  from user_tables
  3  where table_name = 'REGULAR_1';

  PCT_FREE     BLOCKS NUM_ROWS BLOCKS*8192/1048576
---------- ---------- ---------- -------------------
  0  1448   364496      11.3125

PDB1@ORCL> 


Note how not only did the table size shrink to less than 12MB, the PCT_FREE also got  reset to 0 !
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21 February, 2016

Compression -- 1 : BASIC Table Compression

Now, starting a new series of blog posts on Compression.

Beginning with  BASIC Table Compression.

Basic Table Compression was introduced in 9i Release 2 (9.2.0).  It is free with the Enterprise Edition.  Basic Compression works only with Direct Path (Bulk Load) INSERTs.  It does not apply to "normal" INSERT and UPDATE operations.
Basic Compression is actually "de-duplication".  It identifies values that are repeated within the same database block and replaces them with tokens mapped to the list of values.   Note the section that I have underlined.  De-duplication does not span database blocks.

Here is a first demo of Basic Compression using INSERT /*+ APPEND */  (for Direct Path Insert).

I start with a table that is a multiplied copy of DBA_OBJECTS, named as SOURCE_DATA.

PDB1@ORCL> show user
USER is "HEMANT"
PDB1@ORCL> select count(*) from source_data;

  COUNT(*)
----------
    364496

PDB1@ORCL> 
PDB1@ORCL> select tablespace_name, segment_type, bytes/1048576
  2  from user_segments
  3  where segment_name = 'SOURCE_DATA';

TABLESPACE_NAME         SEGMENT_TYPE   BYTES/1048576
------------------------------ ------------------ -------------
HEMANT          TABLE        49

PDB1@ORCL> 


I then create table to hold compressed data.  Note (let me repeat again : Basic Compression works only with DIRECT PATH INSERT).

PDB1@ORCL> create table compressed_1 tablespace hemant compress as select * from source_data where 1=2;

Table created.

PDB1@ORCL> insert /*+ APPEND */ into compressed_1
  2  select * from source_data;

364496 rows created.

PDB1@ORCL> commit;

Commit complete.

PDB1@ORCL>
PDB1@ORCL> col segment_name format a30
PDB1@ORCL> select segment_name, segment_type, bytes/1048576
  2  from user_Segments
  3  where tablespace_name = 'HEMANT';

SEGMENT_NAME         SEGMENT_TYPE   BYTES/1048576
------------------------------ ------------------ -------------
COMPRESSED_1         TABLE        12
SOURCE_DATA         TABLE        49

PDB1@ORCL> 


So, a 49MB table is compressed down to 12MB.  What if I UPDATE these rows ?

PDB1@ORCL> update compressed_1
  2  set owner = owner;

364496 rows updated.

PDB1@ORCL> commit;

Commit complete.

PDB1@ORCL> select segment_name, segment_type, bytes/1048576
  2  from user_segments
  3  where tablespace_name = 'HEMANT';

SEGMENT_NAME         SEGMENT_TYPE   BYTES/1048576
------------------------------ ------------------ -------------
COMPRESSED_1         TABLE        22
SOURCE_DATA         TABLE        49

PDB1@ORCL> 


Updating only a single column without changing the length of the data in that column has increased the size of the table.

Let me continue the UPDATE experiment further, without increasing the length of data in any columns.

PDB1@ORCL> update compressed_1
  2  set owner = owner, object_name = object_name, subobject_name = subobject_name, object_id = object_id,
  3  data_object_id = data_object_id, object_type = object_type, created = created
  4  /  

364496 rows updated.

PDB1@ORCL> commit;

Commit complete.

PDB1@ORCL> select segment_name, segment_type, bytes/1048576
  2  from user_segments
  3  where tablespace_name = 'HEMANT';

SEGMENT_NAME         SEGMENT_TYPE   BYTES/1048576
------------------------------ ------------------ -------------
COMPRESSED_1         TABLE        22
SOURCE_DATA         TABLE        49

PDB1@ORCL> 


No further degradation ? (unless my UPDATE expands the size of data in one or more column(s)).

Note a difference between the two tables :

PDB1@ORCL> select table_name, compression, compress_for, pct_free
  2  from user_tables;

TABLE_NAME         COMPRESS COMPRESS_FOR    PCT_FREE
------------------------------ -------- ------------------------------ ----------
COMPRESSED_1         ENABLED BASIC     0
SOURCE_DATA         DISABLED            10

PDB1@ORCL> 


The Compressed table is created with PCT_FREE=10.  PCT_FREE=0  (Note that this can also have an impact when you issue UPDATEs subsequently, UPDATEs that increase the size of data in one or more columns).

UPDATE : In 12c the syntax for BASIC Compression is "ROW STORE COMPRESS BASIC". Simply specifying "COMPRESS" or "COMPRESS BASIC" is supported for backward compatibility.

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19 February, 2016

RMAN : Unused Block Compression and Null Block Compression

To quote the 11.2 documentation,  "Although it is referred to as block compression, it might be helpful to think of block compression as block skipping".  11.2 differentiates between Unused Block Compression and Null Block Compression.
UPDATE 28-Feb-16 : Please note the list of 5 pre-requisites for Unused Block Compression.

In response to a community thread, here is a quick demo to see both Null Block Compression and Unused Block Compression.

I start with a 100MB tablespace.

[oracle@ora11204 Desktop]$ sqlplus '/ as sysdba'

SQL*Plus: Release 11.2.0.4.0 Production on Fri Feb 19 22:37:47 2016

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> create tablespace hemant;

Tablespace created.

SQL> alter user hemant quota unlimited on hemant;

User altered.

SQL> select file_name, bytes/1048576 from dba_data_files
  2  where tablespace_name = 'HEMANT';

FILE_NAME
--------------------------------------------------------------------------------
BYTES/1048576
-------------
/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
   100


SQL> 


First I take a backup of this empty tablespace.

RMAN> backup tablespace hemant;

Starting backup at 19-FEB-16
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=152 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00011 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
channel ORA_DISK_1: starting piece 1 at 19-FEB-16
channel ORA_DISK_1: finished piece 1 at 19-FEB-16
piece handle=/u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224255_cdgbhhyh_.bkp tag=TAG20160219T224255 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 19-FEB-16

Starting Control File and SPFILE Autobackup at 19-FEB-16
piece handle=/u02/FRA/ORCL/autobackup/2016_02_19/o1_mf_s_904257776_cdgbhkcx_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 19-FEB-16

RMAN> list backup of tablespace hemant;


List of Backup Sets
===================


BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
25      Full    1.03M      DISK        00:00:01     19-FEB-16      
        BP Key: 25   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224255
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224255_cdgbhhyh_.bkp
  List of Datafiles in backup set 25
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4806951    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

RMAN> 

This 100MB datafile backed up to 1.03MB is Null Blocm compression.

I next load data into it and  then take a backup.

[oracle@ora11204 Desktop]$ sqlplus hemant/hemant

SQL*Plus: Release 11.2.0.4.0 Production on Fri Feb 19 22:45:12 2016

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> create table hkc_all_obj tablespace hemant
  2  as select * from dba_objects;

Table created.

SQL> insert into hkc_all_obj select * from hkc_all_obj;

28105 rows created.

SQL> /

56210 rows created.

SQL> /

112420 rows created.

SQL> /

224840 rows created.

SQL> commit;              

Commit complete.

SQL> select segment_name, bytes/1048576
  2  from user_segments
  3  where tablespace_name = 'HEMANT';

SEGMENT_NAME
--------------------------------------------------------------------------------
BYTES/1048576
-------------
HKC_ALL_OBJ
    49


SQL> 
RMAN> backup tablespace hemant;

Starting backup at 19-FEB-16
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=22 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00011 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
channel ORA_DISK_1: starting piece 1 at 19-FEB-16
channel ORA_DISK_1: finished piece 1 at 19-FEB-16
piece handle=/u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224721_cdgbqw0k_.bkp tag=TAG20160219T224721 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:07
Finished backup at 19-FEB-16

Starting Control File and SPFILE Autobackup at 19-FEB-16
piece handle=/u02/FRA/ORCL/autobackup/2016_02_19/o1_mf_s_904258049_cdgbr179_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 19-FEB-16

RMAN> list backup of tablespace hemant;


List of Backup Sets
===================


BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
25      Full    1.03M      DISK        00:00:01     19-FEB-16      
        BP Key: 25   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224255
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224255_cdgbhhyh_.bkp
  List of Datafiles in backup set 25
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4806951    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
27      Full    49.67M     DISK        00:00:04     19-FEB-16      
        BP Key: 27   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224721
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224721_cdgbqw0k_.bkp
  List of Datafiles in backup set 27
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4807559    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

RMAN> 


So, I now have 49.67MB backup of the datafile in the tablespace. What happens if I drop all objects (in this case only the 1 table) in that tablespace, with RECYLEBIN ?

SQL> show parameter recycle

NAME         TYPE  VALUE
------------------------------------ ----------- ------------------------------
buffer_pool_recycle       string
db_recycle_cache_size       big integer 0
recyclebin        string  on
SQL> drop table hkc_all_obj;

Table dropped.

SQL> select object_name, original_name, ts_name, space, space*8192/1048576
  2  from user_recyclebin;

OBJECT_NAME         ORIGINAL_NAME
------------------------------ --------------------------------
TS_NAME        SPACE SPACE*8192/1048576
------------------------------ ---------- ------------------
BIN$LCGWc71HDSzgUwEAAH/27g==$0 HKC_ALL_OBJ
HEMANT         6272    49


SQL> 
RMAN> backup tablespace hemant;

Starting backup at 19-FEB-16
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=26 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00011 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
channel ORA_DISK_1: starting piece 1 at 19-FEB-16
channel ORA_DISK_1: finished piece 1 at 19-FEB-16
piece handle=/u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T225023_cdgbxh72_.bkp tag=TAG20160219T225023 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 19-FEB-16

Starting Control File and SPFILE Autobackup at 19-FEB-16
piece handle=/u02/FRA/ORCL/autobackup/2016_02_19/o1_mf_s_904258224_cdgbxjg4_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 19-FEB-16

RMAN> list backup of tablespace hemant;


List of Backup Sets
===================


BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
25      Full    1.03M      DISK        00:00:01     19-FEB-16      
        BP Key: 25   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224255
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224255_cdgbhhyh_.bkp
  List of Datafiles in backup set 25
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4806951    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
27      Full    49.67M     DISK        00:00:04     19-FEB-16      
        BP Key: 27   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224721
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224721_cdgbqw0k_.bkp
  List of Datafiles in backup set 27
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4807559    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
29      Full    49.67M     DISK        00:00:00     19-FEB-16      
        BP Key: 29   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T225023
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T225023_cdgbxh72_.bkp
  List of Datafiles in backup set 29
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4807909    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

RMAN> 


The latest backup (BackupSet 29) is still 49.67MB although, technically, the tablespace has no Tables/Indexes.  It does have something in the RECYCLEBIN.

Let me purge the RECYCLEBIN and then run a fresh backup.

SQL> select object_name, original_name, ts_name, space, space*8192/1048576
  2  from user_recyclebin;

OBJECT_NAME         ORIGINAL_NAME
------------------------------ --------------------------------
TS_NAME        SPACE SPACE*8192/1048576
------------------------------ ---------- ------------------
BIN$LCGWc71HDSzgUwEAAH/27g==$0 HKC_ALL_OBJ
HEMANT         6272    49


SQL> purge hkc_all_obj;
purge hkc_all_obj
      *
ERROR at line 1:
ORA-38302: invalid PURGE option


SQL> purge table hkc_all_obj;

Table purged.

SQL> select object_name, original_name, ts_name, space, space*8192/1048576
  2  from user_recyclebin;

no rows selected

SQL> 
RMAN> backup tablespace hemant;

Starting backup at 19-FEB-16
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=144 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00011 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
channel ORA_DISK_1: starting piece 1 at 19-FEB-16
channel ORA_DISK_1: finished piece 1 at 19-FEB-16
piece handle=/u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T225323_cdgc33tc_.bkp tag=TAG20160219T225323 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 19-FEB-16

Starting Control File and SPFILE Autobackup at 19-FEB-16
piece handle=/u02/FRA/ORCL/autobackup/2016_02_19/o1_mf_s_904258404_cdgc351n_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 19-FEB-16

RMAN> list backup of tablespace hemant;


List of Backup Sets
===================


BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
25      Full    1.03M      DISK        00:00:01     19-FEB-16      
        BP Key: 25   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224255
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224255_cdgbhhyh_.bkp
  List of Datafiles in backup set 25
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4806951    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
27      Full    49.67M     DISK        00:00:04     19-FEB-16      
        BP Key: 27   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T224721
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T224721_cdgbqw0k_.bkp
  List of Datafiles in backup set 27
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4807559    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
29      Full    49.67M     DISK        00:00:00     19-FEB-16      
        BP Key: 29   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T225023
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T225023_cdgbxh72_.bkp
  List of Datafiles in backup set 29
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4807909    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
31      Full    1.03M      DISK        00:00:00     19-FEB-16      
        BP Key: 31   Status: AVAILABLE  Compressed: NO  Tag: TAG20160219T225323
        Piece Name: /u02/FRA/ORCL/backupset/2016_02_19/o1_mf_nnndf_TAG20160219T225323_cdgc33tc_.bkp
  List of Datafiles in backup set 31
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4808966    19-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf

RMAN> 
[oracle@ora11204 Desktop]$ ls -l /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
-rw-rw----. 1 oracle oracle 104865792 Feb 19 22:53 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cdgb60g4_.dbf
[oracle@ora11204 Desktop]$ 


Aha ! BackupSet 31 is now 1.03MB only.  So, Unused Block Compression has kicked in !  The blocks that belonged to that table are yet formatted and in prior versions that did not have Unused Block Compression would still be backed up even though the table has been dropped.
(Note : I did not shrink the datafile, it is still 100MB).


UPDATE 28-Feb-16 :  Testing for TRUNCATE

SQL> select segment_name, bytes/1048576
  2  from user_segments
  3  where tablespace_name = 'HEMANT';

SEGMENT_NAME           BYTES/1048576
--------------------------------------------------------------------------------- -------------
HKC_ALL_OBJ               49

SQL> 
RMAN> backup tablespace hemant;

Starting backup at 28-FEB-16
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=19 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00011 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cf5nc41d_.dbf
channel ORA_DISK_1: starting piece 1 at 28-FEB-16
channel ORA_DISK_1: finished piece 1 at 28-FEB-16
piece handle=/u01/app/oracle/flash_recovery_area/ORCL/backupset/2016_02_28/o1_mf_nnndf_TAG20160228T190655_cf5o6lw3_.bkp tag=TAG20160228T190655 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:26
Finished backup at 28-FEB-16

Starting Control File and SPFILE Autobackup at 28-FEB-16
piece handle=/u01/app/oracle/flash_recovery_area/ORCL/autobackup/2016_02_28/o1_mf_s_905022445_cf5o7lyq_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 28-FEB-16

RMAN> list backup of tablespace hemant completed after "trunc(sysdate)";


List of Backup Sets
===================


BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
1       Full    49.55M     DISK        00:00:22     28-FEB-16      
        BP Key: 1   Status: AVAILABLE  Compressed: NO  Tag: TAG20160228T190655
        Piece Name: /u01/app/oracle/flash_recovery_area/ORCL/backupset/2016_02_28/o1_mf_nnndf_TAG20160228T190655_cf5o6lw3_.bkp
  List of Datafiles in backup set 1
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4776386    28-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cf5nc41d_.dbf

RMAN> 
SQL> show parameter recyclebin;

NAME         TYPE  VALUE
------------------------------------ ----------- ------------------------------
recyclebin        string  on
SQL> truncate table hkc_all_obj;

Table truncated.

SQL> select segment_name, bytes/1048576
  2  from user_segments
  3  where tablespace_name = 'HEMANT';

SEGMENT_NAME           BYTES/1048576
--------------------------------------------------------------------------------- -------------
HKC_ALL_OBJ            .0625

SQL> 
RMAN> backup tablespace hemant;

Starting backup at 28-FEB-16
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00011 name=/u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cf5nc41d_.dbf
channel ORA_DISK_1: starting piece 1 at 28-FEB-16
channel ORA_DISK_1: finished piece 1 at 28-FEB-16
piece handle=/u01/app/oracle/flash_recovery_area/ORCL/backupset/2016_02_28/o1_mf_nnndf_TAG20160228T190946_cf5octqc_.bkp tag=TAG20160228T190946 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:03
Finished backup at 28-FEB-16

Starting Control File and SPFILE Autobackup at 28-FEB-16
piece handle=/u01/app/oracle/flash_recovery_area/ORCL/autobackup/2016_02_28/o1_mf_s_905022589_cf5oczwq_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 28-FEB-16

RMAN> list backup of tablespace hemant completed after "trunc(sysdate)";


List of Backup Sets
===================


BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
1       Full    49.55M     DISK        00:00:22     28-FEB-16      
        BP Key: 1   Status: AVAILABLE  Compressed: NO  Tag: TAG20160228T190655
        Piece Name: /u01/app/oracle/flash_recovery_area/ORCL/backupset/2016_02_28/o1_mf_nnndf_TAG20160228T190655_cf5o6lw3_.bkp
  List of Datafiles in backup set 1
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4776386    28-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cf5nc41d_.dbf

BS Key  Type LV Size       Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ ---------------
3       Full    1.53M      DISK        00:00:01     28-FEB-16      
        BP Key: 3   Status: AVAILABLE  Compressed: NO  Tag: TAG20160228T190946
        Piece Name: /u01/app/oracle/flash_recovery_area/ORCL/backupset/2016_02_28/o1_mf_nnndf_TAG20160228T190946_cf5octqc_.bkp
  List of Datafiles in backup set 3
  File LV Type Ckp SCN    Ckp Time  Name
  ---- -- ---- ---------- --------- ----
  11      Full 4776656    28-FEB-16 /u01/app/oracle/oradata/ORCL/datafile/o1_mf_hemant_cf5nc41d_.dbf

RMAN> 


The TRUNCATE did reduce the size of the table and the backup !
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14 February, 2016

Trace Files -- 12 : Tracing a Particular Process

Unlike tracing for particular SQL statements, you can also trace by PID  (Oracle PID) or Server Process ID (SPID).

SQL> select s.sid, p.pid
  2  from v$session s join v$process p
  3  on (s.paddr=p.addr)
  4  and s.username = 'HEMANT';

       SID   PID
---------- ----------
 19    22

SQL> 
SQL> alter system set events 'sql_trace {process: orapid=22}';

System altered.

SQL> 
SQL> select s.sid, p.pid, p.spid
  2  from v$session s join v$process p
  3  on (s.paddr=p.addr)
  4  and s.username = 'HR';

       SID   PID SPID
---------- ---------- ------------------------
 14    26 3207

SQL> alter system set events 'sql_trace {process:3207}';

System altered.

SQL> 


Tracing for the processes is disabled with :

SQL> alter system set events 'sql_trace {process: orapid=22} off';

System altered.

SQL> alter system set events 'sql_trace {process:3207} off';

System altered.

SQL> 


Tracing seems to get disabled after the next SQL, not immediately.

Remember : This is SQL Tracing, not Optimizer Tracing.
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07 February, 2016

Trace Files -- 11b : Using DBMS_SQLDIAG to trace the Optimization of an SQL Statement

My previous blogpost covered using ALTER SYSTEM/SESSION to set tracing for a specific SQL_ID that has been determined in advance.   The SQL may be executed in the future after the ALTER SYSTEM/SESSION.

Here is a method for an SQL that has already been executed.

SQL> select count(*) from all_objects_many_list
  2  where created > sysdate-365;

  COUNT(*)
----------
     25548

SQL> begin
  2  dbms_sqldiag.dump_trace(p_sql_id=>'b086mzzp82x7w',
  3                          p_component=>'Optimizer',
  4                         p_file_id=>'OPT_TRACE_b086mzzp82x7w');
  5  end;
  6  /

PL/SQL procedure successfully completed.

SQL> 
SQL> select value from v$diag_info where name = 'Default Trace File';

VALUE
------------------------------------------------------------------------------------
/u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_2987_OPT_TRACE_b086mzzp82x7w.trc

SQL> 


Let's review the trace file.

Registered qb: SEL$1 0x99b9000 (PARSER)
---------------------
QUERY BLOCK SIGNATURE
---------------------
  signature (): qb_name=SEL$1 nbfros=1 flg=0
    fro(0): flg=4 objn=35014 hint_alias="ALL_OBJECTS_MANY_LIST"@"SEL$1"

SPM: statement not found in SMB
SPM: statement not a candidate for auto-capture

**************************
Automatic degree of parallelism (ADOP)
**************************
Automatic degree of parallelism is disabled: Parameter.

PM: Considering predicate move-around in query block SEL$1 (#0)
**************************
Predicate Move-Around (PM)
**************************
OPTIMIZER INFORMATION

******************************************
----- Current SQL Statement for this session (sql_id=0b1t991khf449) -----
/* SQL Analyze(148,0) */ select count(*) from all_objects_many_list
where created > sysdate-365
----- PL/SQL Stack -----
----- PL/SQL Call Stack -----
  object      line  object
  handle    number  name
0x6be0d530       145  package body SYS.DBMS_SQLTUNE_INTERNAL
0x6be0d530     12098  package body SYS.DBMS_SQLTUNE_INTERNAL
0x6be6b738      1229  package body SYS.DBMS_SQLDIAG
0x6becaea8         2  anonymous block
*******************************************
Legend
The following abbreviations are used by optimizer trace.
CBQT - cost-based query transformation
JPPD - join predicate push-down
OJPPD - old-style (non-cost-based) JPPD
FPD - filter push-down
PM - predicate move-around
CVM - complex view merging
SPJ - select-project-join
SJC - set join conversion
SU - subquery unnesting
OBYE - order by elimination
OST - old style star transformation
ST - new (cbqt) star transformation
CNT - count(col) to count(*) transformation
JE - Join Elimination
JF - join factorization
CBY - connect by
SLP - select list pruning
DP - distinct placement
qb - query block
LB - leaf blocks
DK - distinct keys
LB/K - average number of leaf blocks per key
DB/K - average number of data blocks per key
CLUF - clustering factor
NDV - number of distinct values
Resp - response cost
Card - cardinality
Resc - resource cost
NL - nested loops (join)
SM - sort merge (join)
HA - hash (join)
CPUSPEED - CPU Speed
IOTFRSPEED - I/O transfer speed
IOSEEKTIM - I/O seek time
SREADTIM - average single block read time
MREADTIM - average multiblock read time
MBRC - average multiblock read count
MAXTHR - maximum I/O system throughput
SLAVETHR - average slave I/O throughput
dmeth - distribution method
  1: no partitioning required
  2: value partitioned
  4: right is random (round-robin)
  128: left is random (round-robin)
  8: broadcast right and partition left
  16: broadcast left and partition right
  32: partition left using partitioning of right
  64: partition right using partitioning of left
  256: run the join in serial
  0: invalid distribution method
sel - selectivity
ptn - partition
***************************************
PARAMETERS USED BY THE OPTIMIZER
********************************
  *************************************
  PARAMETERS WITH ALTERED VALUES
  ******************************
Compilation Environment Dump
is_recur_flags                      = 8
Bug Fix Control Environment


  *************************************
  PARAMETERS WITH DEFAULT VALUES
  ******************************
Compilation Environment Dump
optimizer_mode_hinted               = false
optimizer_features_hinted           = 0.0.0
parallel_execution_enabled          = true
parallel_query_forced_dop           = 0
parallel_dml_forced_dop             = 0
parallel_ddl_forced_degree          = 0
parallel_ddl_forced_instances       = 0
_query_rewrite_fudge                = 90
optimizer_features_enable           = 11.2.0.4
_optimizer_search_limit             = 5
.... continued to a long list of parameters ........
....................................................
Bug Fix Control Environment
    fix  3834770 = 1
    fix  3746511 = enabled
    fix  4519016 = enabled
.... continued to a long list of bug fixes ........
...................................................
 ***************************************
  PARAMETERS IN OPT_PARAM HINT
  ****************************
***************************************
Column Usage Monitoring is ON: tracking level = 1
***************************************

Considering Query Transformations on query block SEL$1 (#0)
**************************
Query transformations (QT)
**************************
JF: Checking validity of join factorization for query block SEL$1 (#0)
JF: Bypassed: not a UNION or UNION-ALL query block.
ST: not valid since star transformation parameter is FALSE
TE: Checking validity of table expansion for query block SEL$1 (#0)
TE: Bypassed: No partitioned table in query block.
CBQT bypassed for query block SEL$1 (#0): no complex view, sub-queries or UNION (ALL) queries.
CBQT: Validity checks failed for 0b1t991khf449.
CSE: Considering common sub-expression elimination in query block SEL$1 (#0)
*************************
Common Subexpression elimination (CSE)
*************************
CSE:     CSE not performed on query block SEL$1 (#0).
OBYE:   Considering Order-by Elimination from view SEL$1 (#0)
***************************
Order-by elimination (OBYE)
***************************
OBYE:     OBYE bypassed: no order by to eliminate.
CVM: Considering view merge in query block SEL$1 (#0)
OJE: Begin: find best directive for query block SEL$1 (#0)
OJE: End: finding best directive for query block SEL$1 (#0)
CNT:   Considering count(col) to count(*) on query block SEL$1 (#0)
*************************
Count(col) to Count(*) (CNT)
*************************
CNT:     COUNT() to COUNT(*) not done.
query block SEL$1 (#0) unchanged
Considering Query Transformations on query block SEL$1 (#0)
**************************
Query transformations (QT)
**************************
JF: Checking validity of join factorization for query block SEL$1 (#0)
JF: Bypassed: not a UNION or UNION-ALL query block.
ST: not valid since star transformation parameter is FALSE
TE: Checking validity of table expansion for query block SEL$1 (#0)
TE: Bypassed: No partitioned table in query block.
CBQT bypassed for query block SEL$1 (#0): no complex view, sub-queries or UNION (ALL) queries.
CBQT: Validity checks failed for 0b1t991khf449.
CSE: Considering common sub-expression elimination in query block SEL$1 (#0)
*************************
Common Subexpression elimination (CSE)
*************************
CSE:     CSE not performed on query block SEL$1 (#0).
SU: Considering subquery unnesting in query block SEL$1 (#0)
********************
Subquery Unnest (SU)
********************
SJC: Considering set-join conversion in query block SEL$1 (#0)
*************************
Set-Join Conversion (SJC)
*************************
SJC: not performed
PM: Considering predicate move-around in query block SEL$1 (#0)
**************************
Predicate Move-Around (PM)
**************************
PM:     PM bypassed: Outer query contains no views.
PM:     PM bypassed: Outer query contains no views.
query block SEL$1 (#0) unchanged
FPD: Considering simple filter push in query block SEL$1 (#0)
"ALL_OBJECTS_MANY_LIST"."CREATED">SYSDATE@!-365
try to generate transitive predicate from check constraints for query block SEL$1 (#0)
finally: "ALL_OBJECTS_MANY_LIST"."CREATED">SYSDATE@!-365

apadrv-start sqlid=398332482954924169
  :
    call(in-use=2008, alloc=16344), compile(in-use=56240, alloc=59416), execution(in-use=2456, alloc=4032)

*******************************************
Peeked values of the binds in SQL statement
*******************************************

Final query after transformations:******* UNPARSED QUERY IS *******
SELECT COUNT(*) "COUNT(*)" FROM "HEMANT"."ALL_OBJECTS_MANY_LIST" "ALL_OBJECTS_MANY_LIST" WHERE "ALL_OBJECTS_MANY_LIST"."CREATED">SYSDATE@!-365
kkoqbc: optimizing query block SEL$1 (#0)

        :
    call(in-use=2056, alloc=16344), compile(in-use=57320, alloc=59416), execution(in-use=2456, alloc=4032)

kkoqbc-subheap (create addr=0x7f4409c4fb18)
****************
QUERY BLOCK TEXT
****************
select count(*) from all_objects_many_list
where created > sysdate-365
---------------------
QUERY BLOCK SIGNATURE
---------------------
signature (optimizer): qb_name=SEL$1 nbfros=1 flg=0
  fro(0): flg=0 objn=35014 hint_alias="ALL_OBJECTS_MANY_LIST"@"SEL$1"

-----------------------------
SYSTEM STATISTICS INFORMATION
-----------------------------
  Using NOWORKLOAD Stats
  CPUSPEEDNW: 937 millions instructions/sec (default is 100)
  IOTFRSPEED: 4096 bytes per millisecond (default is 4096)
  IOSEEKTIM:  10 milliseconds (default is 10)
  MBRC:       NO VALUE blocks (default is 8)


And here is the actual information about how the Costing is done and Execution Plan determined.

***************************************
BASE STATISTICAL INFORMATION
***********************
Table Stats::
  Table: ALL_OBJECTS_MANY_LIST  Alias: ALL_OBJECTS_MANY_LIST
    #Rows: 7197952  #Blks:  98279  AvgRowLen:  93.00  ChainCnt:  0.00
Index Stats::
  Index: ALL_OBJ_M_L_CRTD_NDX  Col#: 7
    LVLS: 2  #LB: 19093  #DK: 1232  LB/K: 15.00  DB/K: 351.00  CLUF: 432893.00
Access path analysis for ALL_OBJECTS_MANY_LIST
***************************************
SINGLE TABLE ACCESS PATH
  Single Table Cardinality Estimation for ALL_OBJECTS_MANY_LIST[ALL_OBJECTS_MANY_LIST]
  Column (#7): CREATED(
    AvgLen: 8 NDV: 1232 Nulls: 0 Density: 0.000812 Min: 2455803 Max: 2457343
  Table: ALL_OBJECTS_MANY_LIST  Alias: ALL_OBJECTS_MANY_LIST
    Card: Original: 7197952.000000  Rounded: 1313133  Computed: 1313133.42  Non Adjusted: 1313133.42
  Access Path: TableScan
    Cost:  27174.11  Resp: 27174.11  Degree: 0
      Cost_io: 26619.00  Cost_cpu: 6242311042
      Resp_io: 26619.00  Resp_cpu: 6242311042
  Access Path: index (index (FFS))
    Index: ALL_OBJ_M_L_CRTD_NDX
    resc_io: 5173.00  resc_cpu: 4598699894
    ix_sel: 0.000000  ix_sel_with_filters: 1.000000
  Access Path: index (FFS)
    Cost:  5581.95  Resp: 5581.95  Degree: 1
      Cost_io: 5173.00  Cost_cpu: 4598699894
      Resp_io: 5173.00  Resp_cpu: 4598699894
  Access Path: index (IndexOnly)
    Index: ALL_OBJ_M_L_CRTD_NDX
    resc_io: 3486.00  resc_cpu: 287452140
    ix_sel: 0.182432  ix_sel_with_filters: 0.182432
    Cost: 3511.56  Resp: 3511.56  Degree: 1
  Best:: AccessPath: IndexRange
  Index: ALL_OBJ_M_L_CRTD_NDX
         Cost: 3511.56  Degree: 1  Resp: 3511.56  Card: 1313133.42  Bytes: 0

***************************************


OPTIMIZER STATISTICS AND COMPUTATIONS
***************************************
GENERAL PLANS
***************************************
Considering cardinality-based initial join order.
Permutations for Starting Table :0
Join order[1]:  ALL_OBJECTS_MANY_LIST[ALL_OBJECTS_MANY_LIST]#0
***********************
Best so far:  Table#: 0  cost: 3511.5623  card: 1313133.4203  bytes: 10505064
***********************
(newjo-stop-1) k:0, spcnt:0, perm:1, maxperm:2000

*********************************
Number of join permutations tried: 1
*********************************
Enumerating distribution method (advanced)

Trying or-Expansion on query block SEL$1 (#0)
Transfer Optimizer annotations for query block SEL$1 (#0)
id=0 frofkks[i] (index start key) predicate="ALL_OBJECTS_MANY_LIST"."CREATED">SYSDATE@!-365
Final cost for query block SEL$1 (#0) - All Rows Plan:
  Best join order: 1
  Cost: 3511.5623  Degree: 1  Card: 1313133.0000  Bytes: 10505064
  Resc: 3511.5623  Resc_io: 3486.0000  Resc_cpu: 287452140
  Resp: 3511.5623  Resp_io: 3486.0000  Resc_cpu: 287452140
kkoqbc-subheap (delete addr=0x7f4409c4fb18, in-use=26384, alloc=32840)
kkoqbc-end:
        :
    call(in-use=8664, alloc=49288), compile(in-use=59856, alloc=63560), execution(in-use=2456, alloc=4032)

kkoqbc: finish optimizing query block SEL$1 (#0)
apadrv-end
          :
    call(in-use=8664, alloc=49288), compile(in-use=60768, alloc=63560), execution(in-use=2456, alloc=4032)


Starting SQL statement dump

user_id=87 user_name=HEMANT module=SQL*Plus action=
sql_id=0b1t991khf449 plan_hash_value=1689651126 problem_type=3
----- Current SQL Statement for this session (sql_id=0b1t991khf449) -----
/* SQL Analyze(148,0) */ select count(*) from all_objects_many_list
where created > sysdate-365
----- PL/SQL Stack -----
----- PL/SQL Call Stack -----
  object      line  object
  handle    number  name
0x6be0d530       145  package body SYS.DBMS_SQLTUNE_INTERNAL
0x6be0d530     12098  package body SYS.DBMS_SQLTUNE_INTERNAL
0x6be6b738      1229  package body SYS.DBMS_SQLDIAG
0x6becaea8         2  anonymous block
sql_text_length=96
sql=/* SQL Analyze(148,0) */ select count(*) from all_objects_many_list
where created > sysdate-365
----- Explain Plan Dump -----
----- Plan Table -----

============
Plan Table
============
-------------------------------------------------+-----------------------------------+
| Id  | Operation          | Name                | Rows  | Bytes | Cost  | Time      |
-------------------------------------------------+-----------------------------------+
| 0   | SELECT STATEMENT   |                     |       |       |  3512 |           |
| 1   |  SORT AGGREGATE    |                     |     1 |     8 |       |           |
| 2   |   INDEX RANGE SCAN | ALL_OBJ_M_L_CRTD_NDX| 1282K |   10M |  3512 |  00:00:43 |
-------------------------------------------------+-----------------------------------+
Predicate Information:
----------------------
2 - access("CREATED">SYSDATE@!-365)

Content of other_xml column
===========================
  db_version     : 11.2.0.4
  parse_schema   : HEMANT
  plan_hash      : 1689651126
  plan_hash_2    : 1742296710
  Outline Data:
  /*+
    BEGIN_OUTLINE_DATA

*** 2016-02-07 21:29:15.838
      IGNORE_OPTIM_EMBEDDED_HINTS
      OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
      DB_VERSION('11.2.0.4')
      ALL_ROWS
      OUTLINE_LEAF(@"SEL$1")
      INDEX(@"SEL$1" "ALL_OBJECTS_MANY_LIST"@"SEL$1" ("ALL_OBJECTS_MANY_LIST"."CREATED"))
    END_OUTLINE_DATA
  */

Optimizer state dump:
Compilation Environment Dump
optimizer_mode_hinted               = false
optimizer_features_hinted           = 0.0.0
parallel_execution_enabled          = true
parallel_query_forced_dop           = 0
parallel_dml_forced_dop             = 0
parallel_ddl_forced_degree          = 0
parallel_ddl_forced_instances       = 0
_query_rewrite_fudge                = 90
optimizer_features_enable           = 11.2.0.4
_optimizer_search_limit             = 5
...... long list of optimizer parameters  ...........
.....................................................
Bug Fix Control Environment
    fix  3834770 = 1
    fix  3746511 = enabled
    fix  4519016 = enabled
...... long list of Bug Fixes .......................
.....................................................

Query Block Registry:
SEL$1 0x99b9000 (PARSER) [FINAL]

:
    call(in-use=11728, alloc=49288), compile(in-use=90704, alloc=155568), execution(in-use=6408, alloc=8088)

End of Optimizer State Dump
Dumping Hints
=============
====================== END SQL Statement Dump ======================


So, this is also a supported method.  This DBMS_SQLDIAG package is available from 11.2
Unfortunately, however, DUMP_TRACE is not documented !  (see the 11.2 documentation on DBMS_SQLDIAG).

Note : If the SQL Statement and/or Plan have already been aged out / purged from the Shared Pool , a DUMP_TRACE would, obviously, not be able to print anything.
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