Ask Tom table about NOLOGGING and redo generation

I was googling for things related to NOLOGGING operations and found this useful post on the Ask Tom web site: url

There is a nice table in the post that shows when insert operations generate redo log activity. But it isn’t formatted very well so I thought I would format the table here so it lines up better.

Table Mode    Insert Mode     ArchiveLog           mode result
-----------   -------------   -----------------    -----------
LOGGING       APPEND          ARCHIVE LOG          redo generated
NOLOGGING     APPEND          ARCHIVE LOG          no redo
LOGGING       no append       ""                   redo generated
NOLOGGING     no append       ""                   redo generated
LOGGING       APPEND          noarchive log mode   no redo
NOLOGGING     APPEND          noarchive log mode   no redo
LOGGING       no append       noarchive log mode   redo generated
NOLOGGING     no append       noarchive log mode   redo generated

All of this is from Ask Tom. My contribution here is just the formatting.

I ran a couple of tests whose results agree with this table. I ran insert append on a database that was not in archivelog mode and the insert ran for the same amount of time with the table set for LOGGING as it did with the table set for NOLOGGING. I ran the same test on a database that is in archivelog mode and saw a big difference in run time between LOGGING and NOLOGGING. I didn’t prove it but I assume that the redo generation caused the difference in run time.

No archivelog and logging:

insert /*+append*/ into target select * from source;

64000 rows created.

Elapsed: 00:00:00.36

No archivelog and nologging:

insert /*+append*/ into target select * from source;

64000 rows created.

Elapsed: 00:00:00.38

Archivelog and logging:

insert /*+append*/ into target select * from source;

64000 rows created.

Elapsed: 00:00:00.84

Archivelog and nologging:

insert /*+append*/ into target select * from source;

64000 rows created.

Elapsed: 00:00:00.53

I haven’t tested all the table options but I thought it was worth formatting for my reference and for others who find it useful.

Bobby