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How Does Row Migration Affect Performance?

Answer»

In CASE of full table scan, the optimizer ignores rowid of INDIVIDUAL migrated rows. THEREFORE, full table scans are not affected by row migration.
Index READ causes additional I/O's on migrated rows. In case of index read, rowids cannot be ignored. In such a case, the index scan will need to read at least two locations for a migrated row as compared to a single read for a non-migrated row. Therefore, index scans are ADVERSELY affected by row migration.

In case of full table scan, the optimizer ignores rowid of individual migrated rows. Therefore, full table scans are not affected by row migration.
Index read causes additional I/O's on migrated rows. In case of index read, rowids cannot be ignored. In such a case, the index scan will need to read at least two locations for a migrated row as compared to a single read for a non-migrated row. Therefore, index scans are adversely affected by row migration.


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