2026-03-12 20:23:15
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idev/lob_fragmentation_user.sql
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idev/lob_fragmentation_user.sql
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-- +----------------------------------------------------------------------------+
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-- | Jeffrey M. Hunter |
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-- | jhunter@idevelopment.info |
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-- | www.idevelopment.info |
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-- |----------------------------------------------------------------------------|
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-- | Copyright (c) 1998-2012 Jeffrey M. Hunter. All rights reserved. |
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-- |----------------------------------------------------------------------------|
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-- | DATABASE : Oracle |
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-- | FILE : lob_fragmentation_user.sql |
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-- | CLASS : LOBs |
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-- | PURPOSE : When a LOB segment is first created, its initial "allocated" |
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-- | size is 64K, even though there are no rows in the table. As LOB |
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-- | data is entered into the LOB segment, the allocated space for |
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-- | the segment will continue to increase. If over time, the LOB |
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-- | segment starts to experience many deletes and updates, it is |
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-- | possible for the LOB segment to become fragmented and possibly |
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-- | waste a considerable amount of disk space. This occurs when the |
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-- | size of the actual LOB segment data is considerably less than |
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-- | what is allocated by the LOB segment. Consider a situation |
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-- | where a LOB segment has 16GB allocated for the segment but only |
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-- | contains 2GB worth of actual LOB data. Potentially, this is |
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-- | nearly 14GB of wasted allocated space. This could occur when a |
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-- | significant number of rows have been deleted from the table |
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-- | storing the LOB column. |
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-- | |
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-- | This script can be used to identify the size and amount of |
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-- | fragmentation that exists in all LOB segments for a particular |
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-- | user. |
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-- | |
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-- | To reclaim the wasted space within a fragmented LOB segment, |
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-- | use the following SQL command: |
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-- | |
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-- | ALTER TABLE <OWNER>.<TABLE_NAME> MODIFY LOB (<LOB_COLUMN>) (SHRINK SPACE);
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-- | |
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-- | NOTE: The time required to shrink the LOB segment is a function |
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-- | of how much data needs to be coalesced. In many cases, |
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-- | the shrink operation can take minutes or possibly several |
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-- | hours depending on the amount of data that needs to be |
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-- | moved. |
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-- | |
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-- | NOTE : As with any code, ensure to test this script in a development |
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-- | environment before attempting to run it in production. |
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-- +----------------------------------------------------------------------------+
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SET TERMOUT OFF;
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COLUMN current_instance NEW_VALUE current_instance NOPRINT;
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COLUMN current_user NEW_VALUE current_user NOPRINT;
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SELECT rpad(instance_name, 17) current_instance, rpad(user, 13) current_user FROM v$instance;
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SET TERMOUT ON;
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PROMPT
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PROMPT +------------------------------------------------------------------------+
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PROMPT | Report : LOB Fragmentation for the Current User |
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PROMPT | Instance : ¤t_instance |
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PROMPT | User : ¤t_user |
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PROMPT +------------------------------------------------------------------------+
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PROMPT
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SET ECHO OFF
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SET FEEDBACK 6
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SET HEADING ON
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SET LINESIZE 180
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SET PAGESIZE 50000
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SET TERMOUT ON
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SET SERVEROUTPUT ON
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SET TIMING OFF
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SET TRIMOUT ON
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SET TRIMSPOOL ON
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SET VERIFY OFF
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CLEAR COLUMNS
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CLEAR BREAKS
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CLEAR COMPUTES
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declare
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v_actual_length number;
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v_allocated_length number;
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v_lob_fragmentation_pct number;
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v_actual_length_char varchar2(50);
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v_allocated_length_char varchar2(50);
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v_statement varchar2(2000);
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v_table_column_pad_length constant number := 45;
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v_actual_length_pad_length constant number := 20;
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v_allocated_length_pad_length constant number := 20;
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v_fragmentation_pad_length constant number := 15;
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begin
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dbms_output.enable(1000000);
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-- Print column headers
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dbms_output.put_line( rpad('LOB COLUMN - [OWNER.TABLE.COLUMN]', v_table_column_pad_length) || ' ' ||
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lpad('ALLOCATED LOB LENGTH', v_allocated_length_pad_length) || ' ' ||
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lpad('ACTUAL LOB LENGTH', v_actual_length_pad_length) || ' ' ||
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lpad('FRAGMENTATION', v_fragmentation_pad_length)
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);
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dbms_output.put_line( rpad('-', v_table_column_pad_length, '-') || ' ' ||
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lpad('-', v_allocated_length_pad_length, '-') || ' ' ||
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lpad('-', v_actual_length_pad_length, '-') || ' ' ||
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lpad('-', v_fragmentation_pad_length, '-')
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);
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-- Get all LOB segments for the current user
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for v_lob_segment in (select user, l.table_name, l.column_name
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from user_lobs l join user_segments s
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using (segment_name, tablespace_name)
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where l.column_name not like '"%'
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order by 2,3)
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loop
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dbms_output.put(rpad(v_lob_segment.user || '.' || v_lob_segment.table_name || '.' || v_lob_segment.column_name, v_table_column_pad_length));
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dbms_output.put(' ');
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-- Get "allocated size" of the LOB segment
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v_statement := 'begin '
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|| 'select to_char(a.bytes, ''999,999,999,999,999'') '
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|| 'into :col_val2 '
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|| 'from user_segments a join user_lobs b '
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|| 'using (segment_name) '
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|| 'where b.table_name = ''' || v_lob_segment.table_name || ''''
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|| ' and b.column_name = ''' || v_lob_segment.column_name || ''';'
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|| 'end;';
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execute immediate v_statement using out v_allocated_length_char;
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v_allocated_length_char := regexp_replace(v_allocated_length_char, ' ', '');
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v_allocated_length := regexp_replace(v_allocated_length_char, ',', '');
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dbms_output.put(lpad(v_allocated_length_char, v_allocated_length_pad_length));
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dbms_output.put(' ');
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begin
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-- Get "actual size" of the LOB segment
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v_statement := 'begin '
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|| 'select to_char(sum(dbms_lob.getlength(' || v_lob_segment.column_name || ')), ''999,999,999,999,999'' ) '
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|| 'into :col_val1 '
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|| 'from ' || v_lob_segment.table_name || ';'
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|| 'end;';
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execute immediate v_statement using out v_actual_length_char;
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v_actual_length_char := nvl(regexp_replace(v_actual_length_char, ' ', ''), '0');
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v_actual_length := nvl(regexp_replace(v_actual_length_char, ',', ''), 0);
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dbms_output.put(lpad(v_actual_length_char, v_actual_length_pad_length));
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dbms_output.put(' ');
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-- Calculate LOB fragmentation
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if v_actual_length = 0 then
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v_actual_length := v_allocated_length;
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end if;
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v_lob_fragmentation_pct := round(((1-(v_actual_length/v_allocated_length))*100), 2);
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dbms_output.put(lpad(v_lob_fragmentation_pct || ' %', v_fragmentation_pad_length));
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exception
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when others then null;
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end;
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dbms_output.put_line('');
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end loop;
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end;
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/
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