Book Image

PostgreSQL 11 Administration Cookbook

By : Simon Riggs, Gianni Ciolli, Sudheer Kumar Meesala
Book Image

PostgreSQL 11 Administration Cookbook

By: Simon Riggs, Gianni Ciolli, Sudheer Kumar Meesala

Overview of this book

PostgreSQL is a powerful, open source database management system with an enviable reputation for high performance and stability. With many new features in its arsenal, PostgreSQL 11 allows you to scale up your PostgreSQL infrastructure. This book takes a step-by-step, recipe-based approach to effective PostgreSQL administration. The book will introduce you to new features such as logical replication, native table partitioning, additional query parallelism, and much more to help you to understand and control, crash recovery and plan backups. You will learn how to tackle a variety of problems and pain points for any database administrator such as creating tables, managing views, improving performance, and securing your database. As you make steady progress, the book will draw attention to important topics such as monitoring roles, backup, and recovery of your PostgreSQL 11 database to help you understand roles and produce a summary of log files, ensuring high availability, concurrency, and replication. By the end of this book, you will have the necessary knowledge to manage your PostgreSQL 11 database efficiently.
Table of Contents (19 chapters)
Title Page
Copyright and Credits
About Packt

Quickly estimating the number of rows in a table

We don't always need an accurate count of rows, especially on a large table that may take a long time to execute. Administrators often need to estimate how big a table is so that they can estimate how long other operations may take.

How to do it…

We can get a quick estimate of the number of rows in a table using roughly the same calculation that Postgres optimizer uses:

SELECT (CASE WHEN reltuples > 0 THEN pg_relation_size(oid)*reltuples/(8192*relpages) 
END)::bigint AS estimated_row_count
FROM pg_class
WHERE oid = 'mytable'::regclass;

This gives us the following output:

(1 row)

It returns a row count very quickly, no matter how large the table that we are examining is. You may want to create a SQL function for the preceding calculation, so you won't need to retype the SQL code every now and then.

The following function estimates the total number of rows using a mathematical procedure...