A quick and dirty script that you can use for fairly detailed analysis of how well index leaf blocks are used. But it reads every used leaf block in index order, potentially one at a time. Note that it only reports leaf blocks which have rows in them – so it won’t show anything for empty leaf blocks that are both in the structure and on the freelist or marked as free in the bitmap space management blocks, even though it will visit them.
(As copied by Oracle Corp. in Metalink note 989186.1)
Make sure you read the notes.
rem rem Script: index_efficiency_3.sql rem Author: Jonathan Lewis rem Dated: Sept 2003 rem Purpose: Example of how to check leaf block packing rem rem Last tested rem 126.96.36.199 rem 10.2.0.3 rem 188.8.131.52 rem Not tested rem 184.108.40.206 rem 10.2.0.4 rem Not applicable rem 220.127.116.11 -- no sys_op_lbid() rem rem Notes rem Example of analyzing index entries per leaf block. rem rem Set up the schema, table name, and index name before rem running the query. rem rem The code assumes you have no more than 10 columns in rem the index for the purposes of generating "is not null" rem clauses to force the necessary index-only execution path. rem This limit can easily be extended by cloning and editing rem the lines of the "setup" statement. rem rem For a simple b-tree index, the first parameter to the rem sys_op_lbid() function has to be the object_id of the rem index. rem rem The query will work with a sample clause if you are rem worried that the index you want to investigate is too rem large to analyze in a reasonable time. (I take 100 blocks rem per second as a conservative estimate for the I/O rate rem when running this script on very large indexes but have rem seen it running three or four times faster that.) rem rem This version of the code is suitable only for simple rem B-tree indexes - although that index may be reversed, rem have descending columns or virtual (function-based) rem columns, or be a global index on a partitioned table. rem define m_owner = &m_schema define m_table_name = &m_table define m_index_name = &m_index column ind_id new_value m_ind_id select object_id ind_id from dba_objects where owner = upper('&m_owner') and object_name = upper('&m_index_name') and object_type = 'INDEX' ; column col01 new_value m_col01 column col02 new_value m_col02 column col03 new_value m_col03 column col04 new_value m_col04 column col05 new_value m_col05 column col06 new_value m_col06 column col07 new_value m_col07 column col08 new_value m_col08 column col09 new_value m_col09 select nvl(max(decode(column_position, 1,column_name)),'null') col01, nvl(max(decode(column_position, 2,column_name)),'null') col02, nvl(max(decode(column_position, 3,column_name)),'null') col03, nvl(max(decode(column_position, 4,column_name)),'null') col04, nvl(max(decode(column_position, 5,column_name)),'null') col05, nvl(max(decode(column_position, 6,column_name)),'null') col06, nvl(max(decode(column_position, 7,column_name)),'null') col07, nvl(max(decode(column_position, 8,column_name)),'null') col08, nvl(max(decode(column_position, 9,column_name)),'null') col09 from dba_ind_columns where table_owner = upper('&m_owner') and table_name = upper('&m_table_name') and index_name = upper('&m_index_name') order by column_position ; break on report skip 1 compute sum of blocks on report compute sum of row_ct on report spool index_efficiency_3 prompt Owner &m_owner prompt Table &m_table_name prompt Index &m_index_name set verify off select rows_per_block, blocks, rows_per_block * blocks row_ct, sum(blocks) over (order by rows_per_block) cumulative_blocks from ( select rows_per_block, count(*) blocks from ( select /*+ cursor_sharing_exact dynamic_sampling(0) no_monitoring no_expand index_ffs(t1, &m_index_name) noparallel_index(t1, &m_index_name) */ sys_op_lbid( &m_ind_id ,'L',t1.rowid) as block_id, count(*) as rows_per_block from &m_owner..&m_table_name t1 -- &m_owner..&m_table_name sample block (5) t1 where &m_col01 is not null or &m_col02 is not null or &m_col03 is not null or &m_col04 is not null or &m_col05 is not null or &m_col06 is not null or &m_col07 is not null or &m_col08 is not null or &m_col09 is not null group by sys_op_lbid( &m_ind_id ,'L',t1.rowid) ) group by rows_per_block ) order by rows_per_block ; spool off
I’ve supplied a sample of the output, with a few observations on interpreting it, in the article referenced in comment #1 below.