The document discusses the nologging feature in Oracle databases, which minimizes redo log entries during certain operations, leading to improved performance. It details the situations where nologging is applicable, comparing the redo generation between nologging and logging modes through various SQL commands. Furthermore, it emphasizes the conditions under which redo is produced during data manipulation operations, and highlights the significance of using append hints for efficiency.

1. Test: DML with NOLOGGING
NOLOGGING: Oracle will generate a minimal number of redo log entries in order to protect
the data dictionary, and the operation will probably run faster. Logging can be disabled at
the table level or the tablespace level.
If it is done at the tablespace level then we create indexes or tables in this tablespace; they
will be in NOLOGGING mode.
A table or an index can be created with NOLOGGING mode or it can be altered using ALTER
TABLE/INDEX NOLOGGING.
NOLOGGING is active in the following situations and while running one of the following
commands but not after that.
- DIRECT LOAD (SQL*Loader)
- DIRECT LOAD INSERT (using APPEND hint)
- CREATE TABLE ... AS SELECT
- CREATE INDEX
- ALTER TABLE MOVE
- ALTER TABLE ... MOVE PARTITION
- ALTER TABLE ... SPLIT PARTITION
- ALTER TABLE ... ADD PARTITION (if HASH partition)
- ALTER TABLE ... MERGE PARTITION
- ALTER TABLE ... MODIFY PARTITION, ADD SUBPARTITON, COALESCE SUBPARTITON,
REBUILD UNUSABLE INDEXES
- ALTER INDEX ... SPLIT PARTITION
- ALTER INDEX ... REBUILD
- ALTER INDEX ... REBUILD PARTITION
Logging is stopped only while one of the commands above is running.
So if a user runs this:
ALTER INDEX new_index NOLOGGING.
The actual rebuild of the index does not generate redo (all data dictionary changes
associated with the rebuild will do) but after that any DML on the index will generate redo
this includes direct load insert on the table which the index belongs to.
All the following statements will generate redo despite the fact the table is in NOLOGGING
mode:
- INSERT INTO new_table_nolog_test ...,
- UPDATE new_table_nolog_test SET ...,
- DELETE FROM new_table_nolog_test ..
The following will not generate redo (except from dictionary changes and indexes):
- INSERT /*+APPEND+/ ...
- ALTER TABLE new_table_nolog_test MOVE ...
- ALTER TABLE new_table_nolog_test MOVE PARTITION ...
DML on table nologging, that will not generate redo, Really?
Example: NOLOGGING (11G Archive Mode) with DML

2. 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';
- Begin Testing -
- 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.

3. 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, just generate for data dictionary ***
- 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

4. ----------
27076692
REDO SIZE=27076692
- INSERT
SQL> @begin
OLD_VALUE
----------
63034912
SQL> INSERT INTO T_NOLOG SELECT * FROM ALL_OBJECTS;
71000 rows created.
SQL>
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

5. 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 redo size with nologging not difference... with logging.
***
- Show case "APPEND" hints
*** table NOLOGGING and not use APPEND hints ***
SQL> @begin
OLD_VALUE
----------
125604156

6. 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, 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

7. ----------
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" not difference (generate redo). ***
*** If "alter table nologging" before, and then insert (append)... it's work with nologging
(not generate redo, just redo for data dictionary). ***
Example: NOLOGGING (NO Archive Mode) with DML
SQL> archive log list
Database log mode No Archive Mode
Automatic archival Disabled
- Create TABLE -
SQL> @begin
OLD_VALUE
----------
0
SQL> create table T_NOLOG nologging as select * from all_objects;
Table created.

8. SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 0) OLD_VALUE
OLD_VALUE
----------
109020
SQL> @begin
OLD_VALUE
----------
109020
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 - 109020) OLD_VALUE
OLD_VALUE
----------
106360
*** When create table (noarchive mode) LOGGING table not different NOLOGGING table
***
- DML -
SQL> @begin
OLD_VALUE
----------
215380
SQL> DELETE FROM T_NOLOG;
49618 rows deleted.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 215380) OLD_VALUE
OLD_VALUE
----------
18318540
SQL> @begin
OLD_VALUE
----------

9. 18533920
SQL> DELETE FROM T_LOG;
49619 rows deleted.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 18533920) OLD_VALUE
OLD_VALUE
----------
18319920
SQL> @begin
OLD_VALUE
----------
36853840
SQL> INSERT INTO T_NOLOG SELECT * FROM ALL_OBJECTS;
49619 rows created.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 36853840) OLD_VALUE
OLD_VALUE
----------
5468288
SQL> @begin
OLD_VALUE
----------
42322128
SQL> INSERT INTO T_LOG SELECT * FROM ALL_OBJECTS;
49619 rows created.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 42322128) OLD_VALUE
OLD_VALUE
----------
5467828
SQL> @begin

10. OLD_VALUE
----------
93911152
SQL> UPDATE T_NOLOG SET OBJECT_ID=1;
49619 rows updated.
SQL> SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 93911152) OLD_VALUE
OLD_VALUE
----------
15555936
SQL> @begin
OLD_VALUE
----------
109467088
SQL> UPDATE T_LOG SET OBJECT_ID=1;
49619 rows updated.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 109467088) OLD_VALUE
OLD_VALUE
----------
16326484
*** On DML INSERT/UPDATE/DELETE not different between NOLOGGING and LOGGING ***
- INSERT /*+ APPEND */ -
SQL> @begin
OLD_VALUE
----------
125793740
SQL> INSERT INTO T_NOLOG SELECT * FROM ALL_OBJECTS;
49619 rows created.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE

11. new 1: select (value - 125793740) OLD_VALUE
OLD_VALUE
----------
5823672
SQL> @begin
OLD_VALUE
----------
131617412
SQL> INSERT /*+ APPEND */ INTO T_NOLOG SELECT * FROM ALL_OBJECTS;
49619 rows created.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 131617412) OLD_VALUE
OLD_VALUE
----------
28484
SQL> @begin
OLD_VALUE
----------
131709848
SQL> INSERT INTO T_LOG SELECT * FROM ALL_OBJECTS;
49619 rows created.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE
new 1: select (value - 131709848) OLD_VALUE
OLD_VALUE
----------
5823620
SQL> @begin
OLD_VALUE
----------
131645896
SQL> INSERT /*+ APPEND */ INTO T_LOG SELECT * FROM ALL_OBJECTS;
49619 rows created.
SQL> @diff
old 1: select (value - &OLD_VALUE) OLD_VALUE

12. new 1: select (value - 131645896) OLD_VALUE
OLD_VALUE
----------
26816
*** On NoArchive Mode, Don't mind tables be nologging/logging... just use /*+
APPEND */ ,that will not generate redo (just data dictionary) ***
*** On Archive Mode, TABLEs must be nologging... and use /*+ APPEND */, that
will not generate redo (just data dictionary) ***
by Surachart Opun