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Matching LOB Indexes and Segments
I enjoyed Tom Kyte’s example of how you find matching a LOB Index to Segment (Expert Oracle Database Architecture, pp. 542). I’ve noticed variations of it posted in various locations. While it works well for sample scheme that have only one LOB, the following works for any number of LOBs in any schema. This simplifies working with system- and user-defined segment names. The first CASE statement ensures that joins between user-named segment names are possible. The second CASE statement ensures two things: (a) Joins between system generated segment names don’t throw an error when matching unrelated system generated return values found in the DBA_SEGEMENTS view; and (b) Joins between named segments are possible and don’t throw an error.
COL owner FORMAT A5 HEADING "Owner" COL TABLE_NAME FORMAT A5 HEADING "Table|Name" COL column_name FORMAT A10 HEADING "Column|Name" COL segment_name FORMAT A26 HEADING "Segment Name" COL segment_type FORMAT A10 HEADING "Segment|Type" COL bytes HEADING "Segment|Bytes" SELECT l.owner , l.table_name , l.column_name , s.segment_name , s.segment_type , s.bytes FROM dba_lobs l , dba_segments s WHERE REGEXP_SUBSTR(l.segment_name,'([[:alnum:]]|[[:punct:]])+' , CASE WHEN REGEXP_INSTR(s.segment_name,'[[:digit:]]',1) > 0 THEN REGEXP_INSTR(s.segment_name,'[[:digit:]]',1) ELSE 1 END) = REGEXP_SUBSTR(s.segment_name,'([[:alnum:]]|[[:punct:]])+' , CASE WHEN REGEXP_INSTR(s.segment_name,'[[:digit:]]',1) > 0 THEN REGEXP_INSTR(s.segment_name,'[[:digit:]]',1) ELSE 1 END) AND l.table_name = UPPER('&table_name') AND l.owner = UPPER('&owner') ORDER BY l.column_name, s.segment_name; |
It produces the following type of output:
Table Column Segment Segment Name Name Segment Name Type Bytes ------ ---------- ------------------------- ---------- --------- PLSQL ITEM_BLOB SYS_IL0000074435C00007$$ LOBINDEX 65,536 PLSQL ITEM_BLOB SYS_LOB0000074435C00007$$ LOBSEGMENT 2,097,152 PLSQL ITEM_DESC SYS_IL0000074435C00006$$ LOBINDEX 65,536 PLSQL ITEM_DESC SYS_LOB0000074435C00006$$ LOBSEGMENT 720,896 |
This should help you monitor growth of LOBs in your database. The maximum CHUNK size is 32.768. If you elect a value greater than that you raise an ORA-22851 error.
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