SQL scripts for index performance analysis in Oracle

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1. Estimate the Impact of Dropping an Index on Query Performance 

 This script estimates the impact of dropping an index on query performance. Replace with the original query you want to analyze. Execute the script to generate the execution plan for the original query. Then, drop the index in question and re-run the EXPLAIN PLAN for the same query. Compare the two execution plans to understand the performance difference.

-- Query to estimate the impact of dropping an index on query performance
EXPLAIN PLAN FOR
<YOUR_QUERY>;

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

-- Drop the index and re-run the EXPLAIN PLAN to compare the results

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-- Sample Query: Estimate the impact of dropping an index on query performance
EXPLAIN PLAN FOR
SELECT * FROM employees WHERE department_id = 10;

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

-- Output Before Dropping Index:
-- PLAN_TABLE_OUTPUT
-- --------------------------------------------------------------
-- Plan hash value: 1234567890
-- 
-- ---------------------------------------
-- | Id  | Operation         | Name       |
-- ---------------------------------------
-- |   0 | SELECT STATEMENT  |            |
-- |   1 |  TABLE ACCESS FULL| EMPLOYEES  |
-- ---------------------------------------

-- Drop the index
DROP INDEX employees_idx;

-- Output After Dropping Index:
-- PLAN_TABLE_OUTPUT
-- --------------------------------------------------------------
-- Plan hash value: 9876543210
-- 
-- ---------------------------------------
-- | Id  | Operation         | Name       |
-- ---------------------------------------
-- |   0 | SELECT STATEMENT  |            |
-- |   1 |  TABLE ACCESS FULL| EMPLOYEES  |
-- ---------------------------------------

2. Compare the Performance of Two Indexes on the Same Table 

 This script compares the performance of two indexes on the same table. Replace and with different queries that use two different indexes on the same table. Execute the script to generate the execution plans for each query. Compare the plans to determine which index performs better for the specific queries.

-- Query to compare the performance of two indexes on the same table
EXPLAIN PLAN FOR
<YOUR_QUERY_WITH_INDEX_1>;

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

EXPLAIN PLAN FOR
<YOUR_QUERY_WITH_INDEX_2>;

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

-- Compare the two execution plans to assess index performance

-- Sample Query: Compare the performance of two indexes on the same table
EXPLAIN PLAN FOR
SELECT * FROM employees WHERE department_id = 10;

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

-- Output with Index 1 (employees_idx1):
-- PLAN_TABLE_OUTPUT
-- --------------------------------------------------------------
-- Plan hash value: 1234567890
-- 
-- ---------------------------------------
-- | Id  | Operation         | Name       |
-- ---------------------------------------
-- |   0 | SELECT STATEMENT  |            |
-- |   1 |  TABLE ACCESS FULL| EMPLOYEES  |
-- ---------------------------------------

EXPLAIN PLAN FOR
SELECT * FROM employees WHERE job_id = 'IT_PROG';

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

-- Output with Index 2 (employees_idx2):
-- PLAN_TABLE_OUTPUT
-- --------------------------------------------------------------
-- Plan hash value: 9876543210
-- 
-- ---------------------------------------
-- | Id  | Operation         | Name       |
-- ---------------------------------------
-- |   0 | SELECT STATEMENT  |            |
-- |   1 |  TABLE ACCESS FULL| EMPLOYEES  |
-- ---------------------------------------

3. Identify Indexes with a High Number of Row Locks or Contention 

 This script identifies indexes with a high number of row locks or contention. It queries the v$object_usage dynamic performance view to find indexes that have experienced a substantial number of row-level locks. The script can help you identify potential contention issues with certain indexes. Please use these scripts with caution and ensure you understand the impact of changes before making any modifications to your indexes. Always test changes in a controlled environment before applying them to production systems.

-- Query to identify indexes with a high number of row locks or contention
SELECT index_name, table_name, row_locks
FROM v$object_usage
WHERE row_locks > 1000
ORDER BY row_locks DESC;

-- Query to identify indexes with a high number of row locks or contention
SELECT index_name, table_name, row_locks
FROM v$object_usage
WHERE row_locks > 1000
ORDER BY row_locks-- Sample Query: Identify indexes with a high number of row locks or contention
SELECT index_name, table_name, row_locks
FROM v$object_usage
WHERE row_locks > 1000
ORDER BY row_locks DESC;

-- Sample Output:
-- INDEX_NAME    TABLE_NAME    ROW_LOCKS
-- ------------  ------------  ---------
-- EMPLOYEES_PK  EMPLOYEES     54321
-- ORDERS_PK     ORDERS        21098
 DESC;

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