EXPLAIN and ANALYZE commands

In this tutorial, we're going to dive deeper into understanding the PostgreSQL "EXPLAIN" and "ANALYZE" commands. These commands are both critical and versatile tools in the PostgreSQL motley, essentially used for debugging performance issues arising in SQL queries. The following sections will disseminate these commands by explaining their functionalities, exploring basic to advanced executions, and code examples.

Understanding PostgreSQL 'EXPLAIN' Command

The "EXPLAIN" command in PostgreSQL is used to view the query planner's purposed pathway to execute an SQL statement. The output notably includes the cost of each operation, which is essentially an abstract metric representing the effort required to execute the operation.

Here is a basic example:

EXPLAIN SELECT * FROM products;

The output represents an execution plan where we might see elements like 'Seq Scan', followed by the name of the table, and couple of metrics defined as 'cost' and 'rows'. In vast terms, this tells us that PostgreSQL plans to sequentially scan the entire 'products' table.

PostgreSQL 'ANALYZE' Command

The "ANALYZE" command in PostgreSQL is used to update statistics regarding the distribution of data in a table. PostgreSQL uses these statistics to decide how to best execute a query. "ANALYZE" can be used all alone or concurrently with "EXPLAIN" as "EXPLAIN ANALYZE" to receive informed statistics about actual runtime and returned rows versus projected ones.

Here is a simple usage of "ANALYZE":

ANALYZE products;

This commands update statistics about the data distribution in the 'products' table which helps PostgreSQL to choose the most suitable query plan.

Uniting 'EXPLAIN' and 'ANALYZE'

The usage of "EXPLAIN ANALYZE" results in executing the query, as well as showing the query plan and the actual time taken at each step. This can provide a more comprehensive picture of the performance characteristics of your SQL queries.

Example:

EXPLAIN ANALYZE SELECT * FROM products;

The output will include more details like execution time and whether the estimates made by 'EXPLAIN' were accurate or not. It includes metrics like 'actual time', 'rows' (number of rows processed at this step), and 'loops' (number of times this step was repeated).

By understanding and effectively utilizing the above commands, we can gain detailed insight into our PostgreSQL databases' performance and identify opportunities for optimization. It is, however, advised to be cautious while using "EXPLAIN ANALYZE" with modification commands (like UPDATE, INSERT, DELETE) especially on production databases, as it does execute the query.

Remember, while 'EXPLAIN' and 'ANALYZE' can help us understand the query execution plan, improving query performance might require advanced optimization strategies which include but are not limited to indexing, denormalization, and query rewriting.

This tutorial only serves as a basic introduction to these commands, but PostgreSQL offers a variety of options and arguments to be used with these commands for deeper analysis for which, PostgreSQL's official documentation is a valuable resource.