Estimating the logical-log size when logging smart large objects

If you plan to log smart-large-object user data, you must ensure that the log size is considerably larger than the amount of data being written. Smart-large-object metadata is always logged even if the smart large objects are not logged.

Use the following guidelines when you log smart large objects:
  • If you are appending data to a smart large object, the increased logging activity is roughly equal to the amount of data written to the smart large object.
  • If you are updating a smart large object (overwriting data), the increased logging activity is roughly twice the amount of data written to the smart large object. The database server logs both the before-image and after-image of a smart large object for update transactions. When updating the smart large objects, the database server logs only the updated parts of the before and after image.
  • Metadata updates affect logging less. Even though metadata is always logged, the number of bytes logged is usually much smaller than the smart large objects.

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