Book Image

PostgreSQL 10 Administration Cookbook - Fourth Edition

By : Simon Riggs, Gianni Ciolli
Book Image

PostgreSQL 10 Administration Cookbook - Fourth Edition

By: Simon Riggs, Gianni Ciolli

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 10 allows users to scale up their PostgreSQL infrastructure. This book takes a step-by-step, recipe-based approach to effective PostgreSQL administration. Throughout this book, you will be introduced to these new features such as logical replication, native table partitioning, additional query parallelism, and much more. You will learn how to tackle a variety of problems that are basically the pain points for any database administrator - from creating tables to managing views, from improving performance to securing your database. More importantly, the book pays special attention to topics such as monitoring roles, backup, and recovery of your PostgreSQL 10 database, ensuring high availability, concurrency, and replication. By the end of this book, you will know everything you need to know to be the go-to PostgreSQL expert in your organization.
Table of Contents (14 chapters)

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 the Postgres optimizer uses:

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

This gives us the following output:

estimated_count
---------------------
293
(1 row)

It returns a row count...