In Oracle Database, DBAs can enforce standard statistics gathering by setting PREFERENCE_OVERRIDES_PARAMETER to TRUE using DBMS_STATS.SET_GLOBAL_PREFS. This instructs the optimizer to ignore incorrect, hardcoded parameters passed by manual scripts—such as a fixed ESTIMATE_PERCENT—and strictly apply optimized global or table-level preferences like AUTO_SAMPLE_SIZE.” What is PREFERENCE_OVERRIDES_PARAMETER Suppose you want all the users to use AUTO_SAMPLE_SIZE for […]

Sometimes we may have performance issues and we want to check the optimizer statistics preferences at the table level. let’s check out the queries for that How to check optimizer stats preferences at the table level set pages 200 lines 200col owner for a16col table_name for a32col preference_value for a50select owner, table_name, PREFERENCE_NAME, PREFERENCE_VALUEfrom dba_tab_stat_prefswhere

What are optimizer statistics preferences? The statistics preferences of the optimizer determine the preset values of the parameters used by automatic statistics collection and the DBMS_STATS statistics gathering processes. We can configure optimizer information at the table, schema, database (all tables), and global levels. A global preference refers to tables with no preferences as well

When we ran gather stats on the table, it generate table stats, index stats, and column stats. Column statistics are used in the optimizer’s selectivity calculations Let’s see how to find it How to check column statistics in Oracle Column stats can be found from dba_tab_columns or dba_tab_col_statistics SELECT column_name, num_distinct, density, num_nulls, avg_col_len, num_buckets,

Indexes are used to fasten access to the record in Oracle. Optimizer chooses an index over a full table scan based on the Index statistics. The statistics allow the optimizer to calculate the effectiveness of using one index over another. Let’s check out how to find the index statistics How to check Index statistics for

Many times, we might want to check if gather stats ran on the table and when it ran last time. We can find this query dba_tables or user_tables view. let’s see a few queries related to this How to check gather stats on a table/how to check last gather stats on table in Oracle The