This utility allows administrators to examine the file structure used by

PostgreSQL.

Databases are placed in directories named after their OIDs in pg_database,

and the table files within a database's directory are named by "filenode"

numbers, which are stored in pg_class.relfilenode.

Note that while a table's filenode often matches its OID, this is *not*

necessarily the case; some operations, like TRUNCATE, REINDEX, CLUSTER

and some forms of ALTER TABLE, can change the filenode while preserving

the OID. Avoid assuming that filenode and table OID are the same.

When a table exceeds 1Gb, it is divided into gigabyte-sized "segments".

The first segment's file name is the same as the filenode; subsequent

segments are named filenode.1, filenode.2, etc.

Tablespaces make the scenario more complicated. Each non-default

tablespace has a symlink inside the pg_tblspc directory, which points to

the physical tablespace directory (as specified in its CREATE TABLESPACE

command). The symlink is named after the tablespace's OID. Inside the

physical tablespace directory there is another directory for each database

that has elements in the tablespace, named after the database's OID.

Tables within that directory follow the filenode naming scheme. The

"pg_default" tablespace is not addressed via pg_tblspc, but corresponds to

$PGDATA/base.

PostgreSQL. To make use of it, you need to be familiar with the file

structure, which is described in the "Database File Layout" chapter of

the "Internals" section of the PostgreSQL documentation.

Oid2name connects to the database and extracts OID, filenode, and table

name information. You can also have it show database OIDs and tablespace