Database Cluster Layout

In this post, we will discuss the Cluster Database Layout of PostgreSQL.

The layout of database cluster has been shown below. Main files and subdirectories in a part of the document have been listed here:

In here, demo is a database cluster. Under the Database Cluster it has 6 files which are:

1. pg_hba.conf: Used for PosgreSQL's client authentication.
2. pg_ident.conf: Used for controlling PostgreSQL's user name mapping
3. PG_VERSION: Containing version number of PostgreSQL
4. postgresql.conf: Used for settin configuration parameters
5. postgresql.auto.conf: In ALTER SYSTEM, it is stored configuration parameters.
6. postmaster.opts: Record the last command line options for the server.

In here, demo has 17 directories which are:

1. base: Subdirectory containing per-database subdirectories. A database is a subdirectory under the base subdirectory; and the database directory names are identical to the respective OIDs. For example, when the OID of the database is 16384, its subdirectory name is 16384.
2. global: It contains cluster-wide tables, such as pg_database and pg_control.
3. pg_commit_ts: Subdirectory containing transaction commit timestamp data. Version 9.5 or later.
4. pg_dynshmem:Subdirectory containing files used by the dynamic shared memory subsystem. Version 9.4 or later.
5. pg_logical:Subdirectory containing status data for logical decoding. Version 9.4 or later.
6. pg_multixact:Subdirectory containing multitransaction status data (used for shared row locks)
7. pg_notify:Subdirectory containing LISTEN/NOTIFY status data
8. pg_replslot:Subdirectory containing replication slot data. Version 9.4 or later.
9. pg_serial:Subdirectory containing information about committed serializable transactions (version 9.1 or later)
10. pg_snapshots:Subdirectory containing exported snapshots (version 9.2 or later). The PostgreSQL's function pg_export_snapshot creates a snapshot information file in this subdirectory.
11. pg_stat:Subdirectory containing permanent files for the statistics subsystem.
12. pg_stat_tmp:Subdirectory containing temporary files for the statistics subsystem.
13. pg_subtrans: Containing subtransaction status data
14. pg_tblspc: Containing symbolic links to tablespaces
15. pg_twophase: Containing state files for prepared transactions
16. pg_wal: Containing WAL (Write Ahead Logging) segment files. It is renamed from pg_xlog in Version 10.
17. pg_xact: Containing transaction commit state data. It is renamed from pg_clog in Version 10.

✔️ References:

1. https://age.apache.org/
2. https://github.com/apache/age
3. https://www.interdb.jp/pg/index.html