Retrieving Table and Index Sizes with PostgreSQL Functions

Functions Used:

• pg_relation_size(table_oid): This function retrieves the size of a specific table (excluding indexes). table_oid is a unique identifier for the table.
• pg_total_relation_size(table_oid): This function calculates the total disk space used by a table, including its data, indexes, and related structures.
• pg_indexes_size(table_oid): This function specifically calculates the total size of all indexes associated with a particular table.

Finding Table Size:

1. You can use pg_relation_size to get the size of the table itself, but this excludes indexes.
2. Alternatively, use pg_total_relation_size to get the combined size of the table, its data, and all its indexes. This is the most comprehensive approach.

1. Use pg_indexes_size with the table identifier to determine the total disk space consumed by all indexes belonging to that table.

Note:

• Replace table_oid with the actual identifier of your table or use the table schema and name within quotes (e.g., "public"."my_table").
• The results from these functions are in bytes. You can use the pg_size_pretty function to convert them into a more readable format (e.g., kilobytes, megabytes).

Example 1: Get Total Size of a Table (including indexes)

SELECT table_name, pg_size_pretty(pg_total_relation_size('public.my_table')) AS total_size
FROM information_schema.tables
WHERE table_name = 'my_table';

This code retrieves the total size (data and indexes) of the table named "my_table" in the "public" schema. It uses pg_total_relation_size and converts the size to a human-readable format with pg_size_pretty.

Example 2: Get Separate Sizes for Table and Indexes

SELECT table_name,
       pg_size_pretty(pg_table_size('public.my_table')) AS table_size,
       pg_size_pretty(pg_indexes_size('public.my_table')) AS indexes_size
FROM information_schema.tables
WHERE table_name = 'my_table';

This example retrieves both the table size (excluding indexes) and the total size of all indexes for the "my_table" table. It uses pg_table_size and pg_indexes_size with formatting by pg_size_pretty.

Using pg_dump and wc (if applicable):

This method involves creating a schema dump of the table and then using the wc command (available on most Linux systems) to estimate the table size. However, it has limitations:

• It captures the logical size, not the actual disk usage, which might differ.
• It doesn't include indexes.

Here's a basic example:

pg_dump -h <host> -p <port> -U <username> <database> <table_name> > table_dump.sql
wc -l table_dump.sql  # This counts lines in the dump (approximate size)
rm table_dump.sql

Using pgAdmin (GUI tool):

If you're using a graphical administration tool like pgAdmin, you can often find the table size information within the interface. Look for options like "Properties" or "Size" for the table and its indexes.

Monitoring Tools:

Several database monitoring tools can provide insights into table and index sizes. These tools often offer more detailed information and visualizations.

Important points to consider with these alternate methods:

• They might not be as accurate or comprehensive as the built-in functions.
• The pg_dump method excludes indexes.
• Monitoring tools might require additional setup or licensing.