SQL Server 2016 introduced a Query Store concept which helps us to monitor the performance differences between the query execution plans.

It helps you to track the query plan, run time statistics and history of query plan.

You can easily find your new query with the different execution plans and you can identify un-efficient plan and force for the better execution plan.

Once you enable the Query Store, It starts to capture a history of queries, plans and other run time statistics.

You can audit the query plans and can find information like: top n queries, CPU/IO/Memory utilization of queries and query executed in a number of times.

Enable the Query Store:

ALTER DATABASE Database_Name SET QUERY_STORE = ON;

You can use below query to find an information on Query Store:

SELECT Txt.query_text_id, Txt.query_sql_text, Pl.plan_id, Qry.*  
FROM sys.query_store_plan AS Pl  
JOIN sys.query_store_query AS Qry  
    ON Pl.query_id = Qry.query_id  
JOIN sys.query_store_query_text AS Txt  
    ON Qry.query_text_id = Txt.query_text_id;

Like any other RDBMS, PostgreSQL generates a Query Execution Plan for each query that it receives.

It is also used Genetic Query Optimizer (GEQO) that does query planning for heuristic search and It reduce query planning time for large and complex queries.

An Optimizer always tries to choose a good Query Execution Plan.

The structure of Query Execution Plan is like a Tree and It contains different information like: type of scan details, join details, sorting details, aggregation details, Estimated rows details, Estimated start-up cost, Estimated total cost and others.

To know about the Query Execution Plan, is very important for all Database Professionals because It helps us to improve the Query Performance.

With the help of Query Execution Plan, We can make our decisions on Index tuning, Join tuning and other.

In PostgreSQL, we have EXPLAIN and EXPLAIN ANALYZE command to know about the Query Execution Plan.

Here, I have used one table tbl_itemtransactions which you can create using below post.

Example of EXPLAIN: It generates the Estimated Query Execution Plan with out executing an actual SQL Query.

EXPLAIN SELECT COUNT(1) FROM tbl_itemtransactions;

/*
Result: 
"Aggregate  (cost=2555525.00..2555525.01 rows=1 width=0)"
"  ->  Seq Scan on tbl_itemtransactions  
(cost=0.00..2216945.00 rows=135432000 width=0)"
*/

Example of EXPLAIN ANALYZE: It first executes the SQL Query and than It generates the actual Query Execution Plan.

EXPLAIN ANALYZE SELECT COUNT(1) FROM tbl_itemtransactions;

/*
Result: 
"Aggregate  (cost=2555525.00..2555525.01 rows=1 width=0) 
(actual time=52660.132..52660.133 rows=1 loops=1)"
"  ->  Seq Scan on tbl_itemtransactions  
(cost=0.00..2216945.00 rows=135432000 width=0) 
(actual time=0.027..46193.484 rows=135432001 loops=1)"
"Planning time: 0.204 ms"
"Execution time: 52660.237 ms"
*/