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SEGMENT ADVISOR not Working as Expected for LOB or SYS_LOB SEGMENT (Doc ID 988744.1)

Last updated on JULY 25, 2022

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 10.1 to 12.2]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.


Segment Advisor usage including recommendations, space assessment or attempts to SHRINK LOBs to reclaim all available free space result in incorrect, improper or confusing results.

The symptoms usually include the following

Segment Advisor LOB Space Assessment:

  • LOB used or free space before SHRINK operation may be incorrect
  • LOB used or free space after the SHRINK operation for LOB segments may be incorrect or show as the same values as seen before the SHRINK operation

Segment Advisor LOB Space Assessment AFTER implementing Advisor recommendations

  • Problems with actual assessed Free or Used space in LOBs
  • Little or no change in LOB freespace measured after implementing the advisor recommendations


The usual change leading to the detection of this problem is after using Segment Advisor for other Segment types. This problem can occur at any time while using the Segment Advisor Recommendations for LOBs.


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