Physical location of datafiles in PostgreSQL

In this article, we will discuss finding the physical location of data files for a particular database.

In the logical structure, we can see different databases and tables or any other objects under it but as DBA we should also be aware of how to find out the location of data files associated with a database or a table.

In the article table creation in Postgres database we learned to create tables now we use the same tables here to perform a demonstration. Assume we have the below details

Database name- tech_db

Table name - employee

tech_db=# \c tech_db

You are now connected to database "tech_db" as user "postgres".

tech_db=# \dt

          List of relations

 Schema |   Name   | Type  |  Owner

--------+----------+-------+----------

 public | employee | table | postgres

(1 row)

tech_db=# select * from employee;

 emp_id | emp_name | age

--------+----------+-----

    123 | sam      |  25

    124 | John     |  24

(2 rows)

as of now we do not physical location of this database or table, now we will try to find out the same

Read More : Database Creation in PostgreSQL

Data Directory

First of all check data directory using show command

tech_db=# show data_directory;

  data_directory

------------------

 E:/postgres/data

(1 row)

Above we got data directory, as by default folders for each database gets created under data_directory/base location

as we see folder as created with some random numbers which is called as OID , value of OID can be find using below query.

tech_db=# select datname, oid from pg_database where datname='tech_db';

 datname |  oid

---------+-------

 tech_db | 16393

(1 row) 

we can see value of oid for database tech_db is 16393 and in above screenshot we can find the same folder under base directory. Under it you can find number of files and now lets find the file related to our table employee

tech_db=# select relname,oid, relfilenode from pg_class where relname='employee';

 relname  |  oid  | relfilenode

----------+-------+-------------

 employee | 16394 |       16394

(1 row)

pick up the relfilenode from above output, you will be able to see same file under folder 16393