execution environment

This script determines whether an index is a good candidate for a rebuild or for
a bitmap index. All indexes for a given schema or for a subset of schema’s are
analyzed (except indexes under SYS and SYSTEM)

Instructions

Execution Environment:
<SQL, SQL*Plus, iSQL*Plus>

Access Privileges:
Requires DBA privileges in order to be executed.

Usage:
sqlplus <user>/<pw> @rebuild.index.sql

Instructions:
Copy the script into the file ind_an.sql. Execute the script from SQL*Plus connected
with a user with DBA privileges. The script requires to parameters:

1. Name of the output file where the report while be generated
2. Name of the SCHEMA to be analyzed.

PROOFREAD THIS SCRIPT BEFORE USING IT! Due to differences in the way text
editors, e-mail packages, and operating systems handle text formatting (spaces,
tabs, and carriage returns), this script may not be in an executable state
when you first receive it. Check over the script to ensure that errors of
this type are corrected.

Description

REM =============================================================
REM
REM                         rebuild_indx.sql
REM
REM  Copyright (c) Oracle Software, 1998 - 2000
REM
REM  Author  : Jurgen Schelfhout
REM
REM  The sample program in this article is provided for educational
REM  purposes only and is NOT supported by Oracle Support Services.
REM  It has been tested internally, however, and works as documented.
REM  We do not guarantee that it will work for you, so be sure to test
REM  it in your environment before relying on it.
REM
REM  This script will analyze all the indexes for a given schema
REM  or for a subset of schema's. After this the dynamic view
REM  index_stats is consulted to see if an index is a good
REM  candidate for a rebuild or for a bitmap index.
REM
REM  Database Version : 7.3.X and above.
REM
REM  NOTE:  If running this on 10g, you must exclude the
REM  objects in the Recycle Bin
REM        cursor c_indx is
REM          select owner, table_name, index_name
REM            from dba_indexes
REM           where owner like upper('&schema')
REM             and table_name not like 'BIN$%'
REM             and owner not in ('SYS','SYSTEM');
REM
REM  Additional References for Recycle Bin functionality:
REM  Note.265254.1 Flashback Table feature in Oracle Database 10g
REM  Note.265253.1 10g Recyclebin Features And How To Disable it(_recyclebin)
REM
REM =============================================================

prompt
ACCEPT spoolfile CHAR prompt 'Output-file : ';
ACCEPT schema CHAR prompt 'Schema name (% allowed) : ';
prompt
prompt
prompt Rebuild the index when :
prompt   - deleted entries represent 20% or more of the current entries
prompt   - the index depth is more then 4 levels.
prompt Possible candidate for bitmap index :
prompt   - when distinctiveness is more than 99%
prompt

spool &spoolfile;
set serveroutput on;
set verify off;
set linesize 140;
declare
  c_name        INTEGER;
  ignore        INTEGER;
  height        index_stats.height%TYPE := 0;
  lf_rows       index_stats.lf_rows%TYPE := 0;
  del_lf_rows   index_stats.del_lf_rows%TYPE := 0;
  distinct_keys index_stats.distinct_keys%TYPE := 0;
  cursor c_indx is
    select owner, table_name, index_name
      from dba_indexes
     where owner like upper('&schema')
       and owner not in ('SYS', 'SYSTEM');
begin
  dbms_output.enable(1000000);
  dbms_output.put_line('Owner           Index Name                              % Deleted Entries Blevel Distinctiveness');
  dbms_output.put_line('--------------  ---------------------------------            ------------  -----           -----');

  c_name := DBMS_SQL.OPEN_CURSOR;
  for r_indx in c_indx loop
    DBMS_SQL.PARSE(c_name,
                   'analyze index ' || r_indx.owner || '.' ||
                   r_indx.index_name || ' validate structure',
                   DBMS_SQL.NATIVE);
    ignore := DBMS_SQL.EXECUTE(c_name);

    select HEIGHT,
           decode(LF_ROWS, 0, 1, LF_ROWS),
           DEL_LF_ROWS,
           decode(DISTINCT_KEYS, 0, 1, DISTINCT_KEYS)
      into height, lf_rows, del_lf_rows, distinct_keys
      from index_stats;
    /*
    - Index is considered as candidate for rebuild when :
    -   - when deleted entries represent 20% or more of the current entries
    -   - when the index depth is more then 4 levels.(height starts counting from 1 so > 5)
    - Index is (possible) candidate for a bitmap index when :
    -   - distinctiveness is more than 99%
    */
    if (height > 5) OR ((del_lf_rows / lf_rows) > 0.2) then
      dbms_output.put_line(rpad(r_indx.owner, 16, ' ') ||
                           rpad(r_indx.index_name, 40, ' ') ||
                           lpad(round((del_lf_rows / lf_rows) * 100, 3),
                                17,
                                ' ') || lpad(height - 1, 7, ' ') ||
                           lpad(round((lf_rows - distinct_keys) * 100 /
                                      lf_rows,
                                      3),
                                16,
                                ' '));
    end if;

  end loop;
  DBMS_SQL.CLOSE_CURSOR(c_name);
end;
/
spool off;
set verify on;

Sample Output:

SQL> @rebuild_index

Output-file : index_rebuild
Schema name (% allowed) : maclean

Rebuild the index when :
- deleted entries represent 20% or more of the current entries
- the index depth is more then 4 levels.
Possible candidate for bitmap index :
- when distinctiveness is more than 99%

Owner           Index Name                              % Deleted Entries Blevel Distinctiveness
--------------  ---------------------------------            ------------  -----           -----
MACLEAN         SYS_MTABLE_00000CFD4_IND_2                             25      0              25
MACLEAN         SYS_MTABLE_00000D3F3_IND_2                         33.333      0          33.333
PL/SQL procedure successfully completed.

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