What is row migration?If an What is the result of this?Whenever data of a migrated row are to be read, this requires an additional read (one for the original location just holding the pointer to the real location, and one for the real data). Thus, migrated rows can cause acute performance degration - the more you have the more you will feel the results. This means, they should be corrected immediately if they are being reported. What factors can influence this?First, the settings for So how to fix this?For this, you first have to analyse your tables: ANALYZE TABLE tablename COMPUTE STATISTICS;
utlchain.sql then may help you to automatically eliminate migration.
Make sure to correct PCTFREE before running this script - otherwise it is
very likely that this problem will re-occur soon.
SELECT num_rows,chain_cnt FROM dba_tables WHERE table_name='tablename'; |