Unindexed foreign keys can lead to bad database performance due to lock contention and full table scans performed on the child table.
Here is a diagram which illustrate the situation:
Continue reading Unindexed foreign keys
This script list the top 10 columns most used in equality predicates or equijoin predicates and which are not indexed.
If you want to be more precise in your analyze you can limit the list to table containing more than a defined number of rows by adding the dba_tables table and filter on the num_rows column.
Missing Index script
ACCEPT SCHEMA_NAME PROMPT 'Choose the schema to analyze:'
select * from (
select 'the column ' || c.name || ' of the table ' || us.name || '.' || o.name || ' was used ' || u.equality_preds || ' times in an equality predicate and ' || u.equijoin_preds || ' times in an equijoin predicate and is not indexed' as colum_to_index
from sys.col_usage$ u,
where u.obj# = o.obj#
and u.obj# = c.obj#
and us.user# = o.owner#
and u.intcol# = c.col#
and c.name not in (select column_name from dba_ind_columns where index_owner ='&SCHEMA_NAME')
and (u.equality_preds > 100 OR u.equijoin_preds > 100)
order by u.equality_preds+u.equijoin_preds desc)
WHERE rownum <11;
Description of the DBMS_MONITOR package
DBMS_MONITOR come for replacement of DBMS_SUPPORT with new functionnalities and easier management.
DBMS_MONITOR can be used to trace sessions or make traces with larger scope.
First let’s have a look to the available procedures of DBMS_MONITOR. Each procedure exists twice, one to enable the trace and one to disable it.
Continue reading Create trace using DBMS_MONITOR