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Blob size verses segment size

edited Jun 25, 2009 10:58AM in Database Tuning (MOSC) 6 commentsAnswered
 I have a brand new table in an 9i (9.2.0.7.0)  database that I just added 249317 records.  The table has a blob field, and 26180 of the inserted records have blob data that is 48960 bytes.  When I run a query to calculate the total size of blob data I get 1.19 GB which is expected.

When I checked to see how much space the segment is using from user_segments I get:

SEGMENT_NAME           GBBLOCKSEXTENTS
SYS_LOB0000008230C00027$$6.10352E-0581
SYS_LOB0000008230C00027$$5.481445313718464271
SYS_LOB0000008230C00027$$6.10352E-0581

Why is the Segment 5.48Gig?  Do I have 4 Gig of overhead, or 4 Gig of free space?  Why has it allocated 271 extents?

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