INSERT/UPDATE/DELETE will generate redo log on NOLOGGING mode ?

After I read about Redo & Undo in Expert Oracle Database Architecture book by Kyte, He told about NOLOGGING...

Nologging doesn't mean all operations in that object will not generate redo log.

And Francisco Munoz A 's Paper told ... Nologging will generate a minimal number of redo log entries in order to protect the data dictionary.

That make my curious about nologging mode with DML. I use it on some tables and some indexes... So I should know a real thing about it by myself.

Francisco Munoz A 's Paper and Oracle Docs Idea ... INSERT/UPDATE/DELETE will generate a real redo with table/index NOLOGGING mode, except INSERT /*+APPEND+/

Begin test... NOLOGGING + DML on 11g Archivelog Mode.

SQL> archive log list
Database log mode Archive Mode
Automatic archival Enabled

Script:

--new.sql
column OLD_VALUE new_value OLD_VALUE
select value OLD_VALUE
from v$mystat, v$statname
where v$mystat.statistic# = v$statname.statistic#
and v$statname.name = 'redo size';

--diff.sql
select (value - &OLD_VALUE) OLD_VALUE
from v$mystat, v$statname
where v$mystat.statistic# = v$statname.statistic#
and v$statname.name = 'redo size';

- Create TABLE -

SQL> @begin

OLD_VALUE
----------
0

SQL> create table T_NOLOG nologging as select * from all_objects;

Table created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 0) OLD_VALUE

OLD_VALUE
----------
133120

REDO SIZE=133120

SQL> @begin

OLD_VALUE
----------
133120

SQL> create table T_LOG logging as select * from all_objects;

Table created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 133120) OLD_VALUE

OLD_VALUE
----------
8748596

REDO SIZE=8748596

Create table with NOLOGGING... not generate redo log (just generate redo log for data dictionary)

After create table... It's time to test with DML:

- DELETE -

SQL> @begin

OLD_VALUE
----------
8881716

SQL> DELETE FROM T_NOLOG ;

70999 rows deleted.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 8881716) OLD_VALUE

OLD_VALUE
----------
27076168

REDO SIZE=27076168

SQL> @begin

OLD_VALUE
----------
35958052

SQL> DELETE FROM T_LOG;

71000 rows deleted.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 35958052) OLD_VALUE

OLD_VALUE
----------
27076692

REDO SIZE=27076692

- INSERT -

SQL> @begin

OLD_VALUE
----------
63034912

SQL> INSERT INTO T_NOLOG SELECT * FROM ALL_OBJECTS;

71000 rows created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 63034912) OLD_VALUE

OLD_VALUE
----------
8493412

REDO SIZE=8493412

SQL> @begin

OLD_VALUE
----------
71528324

SQL>INSERT INTO T_LOG SELECT * FROM ALL_OBJECTS;

71000 rows created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 71528324) OLD_VALUE

OLD_VALUE
----------
8493360

REDO SIZE=8493360

- UPDATE -

SQL> @begin

OLD_VALUE
----------
80021684

SQL> UPDATE T_NOLOG SET OBJECT_ID=1;

71000 rows updated.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 80021684) OLD_VALUE

OLD_VALUE
----------
24671048

REDO SIZE=24671048

SQL> @begin

OLD_VALUE
----------
104692732

SQL> UPDATE T_LOG SET OBJECT_ID=1;

71000 rows updated.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 104692732) OLD_VALUE

OLD_VALUE
----------
20911424

REDO SIZE=20911424

On DML INSERT/UPDATE/DELETE ... Oracle generated redo log on nologging mode not difference... on logging mode.

And I need to know about it on INSERT /*+ APPEND */:

- INSERT "APPEND" hints -

- table NOLOGGING mode and not use APPEND hints

SQL> @begin

OLD_VALUE
----------
125604156

SQL> INSERT INTO T_NOLOG SELECT * FROM ALL_OBJECTS;

71000 rows created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 125604156) OLD_VALUE

OLD_VALUE
----------
8586036

REDO SIZE=8586036

SQL> @begin

OLD_VALUE
----------
142830588

SQL> INSERT /*+ APPEND */ INTO T_NOLOG SELECT * FROM ALL_OBJECTS;

71000 rows created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 142830588) OLD_VALUE

OLD_VALUE
----------
29448

REDO SIZE=29448


- table LOGGING mode, and use APPEND hints

SQL> @begin

OLD_VALUE
----------
134190192

SQL> INSERT /*+ APPEND */ INTO T_LOG SELECT * FROM ALL_OBJECTS;

71000 rows created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 134190192) OLD_VALUE

OLD_VALUE
----------
8640396

REDO SIZE=8640396

*** make table logging to nologging ***

SQL> alter table t_log nologging ;

Table altered.

SQL> @begin

OLD_VALUE
----------
142874676

SQL> INSERT /*+ APPEND */ INTO T_LOG SELECT * FROM ALL_OBJECTS;

71000 rows created.

SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 142874676) OLD_VALUE

OLD_VALUE
----------
27956

REDO SIZE=27956

APPEND hints on table "LOGGING" mode "select logging from dba_tables" (NO) ... not difference (generate redo)

If "alter table nologging" before, and then insert (append)

So, Oracle will generate a minimal number of redo log... with INSERT /*+ APPEND */ when table be nologging ... select logging from dba_tables (NO)

That just testing... But helpful to understand something ;)

reference: http://docs.google.com/View?id=dhg2wncg_30mpkpd5cc