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nologging
Posted on 2010-11-28
When we create table we use nologging attribute.
Could you please explain why we use that?
Could you please explain why we use that?
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6 Comments
it means that IF you have the table in NOLOGGING mode AND you run the INSERT in "APPEND" mode (hint /*+APPEND*/, then the insert (data) is not logged in the redo log, but only the statement as such.
normally, all DML statements are logged along with the data they modify. this can, escecially for large data updates/deletes/insert result in big archive logs.
normally, all DML statements are logged along with the data they modify. this can, escecially for large data updates/deletes/insert result in big archive logs.
There are many uses in verity of different ways for LOGGING/NOLOGGING
Exert is from Tom .
<quote>
LOGGING|NOLOGGING
LOGGING|NOLOGGING specifies that subsequent Direct Loader (SQL*Loader) and direct-load
INSERT operations against a nonpartitioned index, a range or hash index partition, or
all partitions or subpartitions of a composite-partitioned index will be logged (LOGGING)
or not logged (NOLOGGING) in the redo log file.
In NOLOGGING mode, data is modified with minimal logging (to mark new extents invalid
and to record dictionary changes). When applied during media recovery, the extent
invalidation records mark a range of blocks as logically corrupt, because the redo data
is not logged. Therefore, if you cannot afford to lose this index, you must take a backup
after the operation in NOLOGGING mode.
If the database is run in ARCHIVELOG mode, media recovery from a backup taken before an
operation in LOGGING mode will re-create the index. However, media recovery from a backup
taken before an operation in NOLOGGING mode will not re-create the index.
An index segment can have logging attributes different from those of the base table and
different from those of other index segments for the same base table.
</quote>
Exert is from Tom .
<quote>
LOGGING|NOLOGGING
LOGGING|NOLOGGING specifies that subsequent Direct Loader (SQL*Loader) and direct-load
INSERT operations against a nonpartitioned index, a range or hash index partition, or
all partitions or subpartitions of a composite-partitioned index will be logged (LOGGING)
or not logged (NOLOGGING) in the redo log file.
In NOLOGGING mode, data is modified with minimal logging (to mark new extents invalid
and to record dictionary changes). When applied during media recovery, the extent
invalidation records mark a range of blocks as logically corrupt, because the redo data
is not logged. Therefore, if you cannot afford to lose this index, you must take a backup
after the operation in NOLOGGING mode.
If the database is run in ARCHIVELOG mode, media recovery from a backup taken before an
operation in LOGGING mode will re-create the index. However, media recovery from a backup
taken before an operation in NOLOGGING mode will not re-create the index.
An index segment can have logging attributes different from those of the base table and
different from those of other index segments for the same base table.
</quote>
DBA's tend to look at nologging options for tables to reduce the overhaed on archive logging process.
In environments like bulk data loading, dataware house environments, because of the huge data pumped in to the database, check point tuning and archiver tuning will always be a challenge to the DBA's. If business can afford to reload the data to certain hot tables incase of crash/failure, then it is wonderful opportunity for DBA's to enable no logging on those tables.So data will not flow through the redologs/archive logs, burden on archiver writing will be reduced which will improve the response time of the database. Majority of the times, log file sync, log file parallel write are the top events wainting in the databases where high data loading takes places.
NoLogging is one quick/calculated risk method to quickly tackle the CheckPoint/Archiver tuning.
In environments like bulk data loading, dataware house environments, because of the huge data pumped in to the database, check point tuning and archiver tuning will always be a challenge to the DBA's. If business can afford to reload the data to certain hot tables incase of crash/failure, then it is wonderful opportunity for DBA's to enable no logging on those tables.So data will not flow through the redologs/archive logs, burden on archiver writing will be reduced which will improve the response time of the database. Majority of the times, log file sync, log file parallel write are the top events wainting in the databases where high data loading takes places.
NoLogging is one quick/calculated risk method to quickly tackle the CheckPoint/Archiver tuning.
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