Tag Archives: PostgreSQL data directory

Database Directory Layout

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PostgreSQL Physical Directory Layout

Installation Directory Layout

[postgres@pgdb02 ~]$ ls -ltr /usr/pgsql-17/
total 16
drwxr-xr-x. 3 postgres postgres 23 Jun 4 20:38 doc
drwxr-xr-x. 8 postgres postgres 4096 Jun 22 21:08 share
drwxr-xr-x. 2 postgres postgres 4096 Jun 22 21:08 bin
drwxr-xr-x. 3 postgres postgres 4096 Jun 22 21:08 lib
[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ ls -lt /usr/pgsql-17/bin
total 14492
-rwxr-xr-x. 1 postgres postgres 71072 May 21 13:49 clusterdb
-rwxr-xr-x. 1 postgres postgres 75240 May 21 13:49 createdb
-rwxr-xr-x. 1 postgres postgres 75624 May 21 13:49 createuser
-rwxr-xr-x. 1 postgres postgres 66632 May 21 13:49 dropdb
-rwxr-xr-x. 1 postgres postgres 66576 May 21 13:49 dropuser
-rwxr-xr-x. 1 postgres postgres 113288 May 21 13:49 initdb
-rwxr-xr-x. 1 postgres postgres 41400 May 21 13:49 oid2name
-rwxr-xr-x. 1 postgres postgres 96824 May 21 13:49 pg_amcheck
-rwxr-xr-x. 1 postgres postgres 41056 May 21 13:49 pg_archivecleanup
-rwxr-xr-x. 1 postgres postgres 142928 May 21 13:49 pg_basebackup
-rwxr-xr-x. 1 postgres postgres 162984 May 21 13:49 pgbench
-rwxr-xr-x. 1 postgres postgres 49632 May 21 13:49 pg_checksums
-rwxr-xr-x. 1 postgres postgres 116872 May 21 13:49 pg_combinebackup
-rwxr-xr-x. 1 postgres postgres 36656 May 21 13:49 pg_config
-rwxr-xr-x. 1 postgres postgres 44984 May 21 13:49 pg_controldata
-rwxr-xr-x. 1 postgres postgres 70768 May 21 13:49 pg_createsubscriber
-rwxr-xr-x. 1 postgres postgres 62296 May 21 13:49 pg_ctl
-rwxr-xr-x. 1 postgres postgres 447368 May 21 13:49 pg_dump
-rwxr-xr-x. 1 postgres postgres 117680 May 21 13:49 pg_dumpall
-rwxr-xr-x. 1 postgres postgres 36952 May 21 13:49 pg_isready
-rwxr-xr-x. 1 postgres postgres 92000 May 21 13:49 pg_receivewal
-rwxr-xr-x. 1 postgres postgres 54544 May 21 13:49 pg_recvlogical
-rwxr-xr-x. 1 postgres postgres 53808 May 21 13:49 pg_resetwal
-rwxr-xr-x. 1 postgres postgres 194496 May 21 13:49 pg_restore
-rwxr-xr-x. 1 postgres postgres 108584 May 21 13:49 pg_rewind
-rwxr-xr-x. 1 postgres postgres 41120 May 21 13:49 pg_test_fsync
-rwxr-xr-x. 1 postgres postgres 32632 May 21 13:49 pg_test_timing
-rwxr-xr-x. 1 postgres postgres 171856 May 21 13:49 pg_upgrade
-rwxr-xr-x. 1 postgres postgres 95928 May 21 13:49 pg_verifybackup
-rwxr-xr-x. 1 postgres postgres 95968 May 21 13:49 pg_waldump
-rwxr-xr-x. 1 postgres postgres 41184 May 21 13:49 pg_walsummary
-rwxr-xr-x. 1 postgres postgres 10875088 May 21 13:49 postgres
-rwxr-xr-x. 1 postgres postgres 729400 May 21 13:49 psql
-rwxr-xr-x. 1 postgres postgres 83816 May 21 13:49 reindexdb
-rwxr-xr-x. 1 postgres postgres 88344 May 21 13:49 vacuumdb
-rwxr-xr-x. 1 postgres postgres 41200 May 21 13:49 vacuumlo
-rwxr-xr-x. 1 postgres postgres 2167 May 21 13:49 postgresql-17-check-db-dir
-rwxr-xr-x. 1 postgres postgres 9617 May 21 13:49 postgresql-17-setup
[postgres@pgdb02 ~]$

Database (Data) Directory Layout

[postgres@pgdb02 ~]$ ls -l /pgData/pgsql17/data
total 68
drwx------. 9 postgres postgres    89 Jun 30 19:40 base
-rw-------. 1 postgres postgres    30 Jul  3 14:30 current_logfiles
drwx------. 2 postgres postgres  4096 Jul  3 14:58 global
drwx------. 2 postgres postgres   162 Jul  3 00:00 log
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_commit_ts
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_dynshmem
-rw-------. 1 postgres postgres  5798 Jun 29 23:45 pg_hba.conf
-rw-------. 1 postgres postgres  2640 Jun 22 21:11 pg_ident.conf
drwx------. 4 postgres postgres    68 Jul  3 14:30 pg_logical
drwx------. 4 postgres postgres    36 Jun 22 21:11 pg_multixact
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_notify
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_replslot
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_serial
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_snapshots
drwx------. 2 postgres postgres     6 Jul  3 14:29 pg_stat
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_stat_tmp
drwx------. 2 postgres postgres    18 Jun 22 21:11 pg_subtrans
drwx------. 2 postgres postgres    19 Jul  2 18:32 pg_tblspc
drwx------. 2 postgres postgres     6 Jun 22 21:11 pg_twophase
-rw-------. 1 postgres postgres     3 Jun 22 21:11 PG_VERSION
lrwxrwxrwx. 1 postgres postgres    18 Jun 22 21:11 pg_wal -> /pgWal/pgsql17/wal
drwx------. 2 postgres postgres    18 Jun 22 21:11 pg_xact
-rw-------. 1 postgres postgres    88 Jun 22 21:11 postgresql.auto.conf
-rw-------. 1 postgres postgres 30881 Jun 29 23:37 postgresql.conf
-rw-------. 1 postgres postgres    55 Jul  3 14:30 postmaster.opts
-rw-------. 1 postgres postgres    89 Jul  3 14:30 postmaster.pid
[postgres@pgdb02 ~]$
NameDirectory or FileDescription
baseDirectoryContains subdirectories for each database. Each database is stored using its own database OID.
current_logfilesFileStores information about the log file currently being written by the logging collector process.
globalDirectoryContains cluster-wide shared system catalog tables such as pg_database, pg_authid, pg_tablespace, etc.
logDirectoryStores PostgreSQL server logs and error log files.
pg_commit_tsDirectoryStores transaction commit timestamp data when track_commit_timestamp is enabled.
pg_dynshmemDirectoryStores files used by PostgreSQL dynamic shared memory subsystem.
pg_hba.confFileClient authentication configuration file. Controls which users and hosts can connect.
pg_ident.confFileStores user name mapping rules between operating system users and database users.
pg_logicalDirectoryStores metadata and status information used for logical replication and logical decoding.
pg_multixactDirectoryStores multitransaction status information used for shared row-level locking.
pg_notifyDirectoryStores LISTEN and NOTIFY asynchronous notification status data.
pg_replslotDirectoryStores physical and logical replication slot information.
pg_serialDirectoryStores metadata related to committed serializable transactions.
pg_snapshotsDirectoryStores exported transaction snapshot files.
pg_statDirectoryStores permanent statistics data used by PostgreSQL statistics subsystem.
pg_stat_tmpDirectoryStores temporary statistics files generated by statistics collector.
pg_subtransDirectoryStores subtransaction status information for nested transactions.
pg_tblspcDirectoryContains symbolic links pointing to user-created tablespaces.
pg_twophaseDirectoryStores prepared transaction state files used for two-phase commit.
PG_VERSIONFileStores the PostgreSQL major version number of the database cluster.
pg_walDirectory (Symlink)Stores WAL (Write Ahead Log) files for crash recovery and replication. Example: /pgWal/pgsql17/wal
pg_xactDirectoryStores transaction commit status information and transaction metadata logs.
postgresql.auto.confFileStores configuration parameters automatically updated by ALTER SYSTEM.
postgresql.confFileMain PostgreSQL configuration file containing server parameter settings.
postmaster.optsFileStores command-line options used when PostgreSQL server was last started.
postmaster.pidFileStores Postmaster PID, startup time, port number, socket path, listen address, and shared memory details.

Difference between Base Directory and Global Directory

In PostgreSQL, both the Base Directory and the Global Directory reside within the PGDATA (the data cluster) folder. The primary difference lies in the scope and type of data they store.

postgres=# \db
       List of tablespaces
    Name    |  Owner   | Location
------------+----------+----------
 pg_default | postgres | <----- pg_default physical location: Located at $PGDATA/base/
 pg_global  | postgres | <----- pg_global physical location: Located at $PGDATA/global/
(2 rows)

postgres=#

-- List of Files and Directoires from Global Directory

[postgres@lxceftsgvdb01 ~]$ ls -la /pgData/pgsql17/data/global
total 580
drwx------.  2 postgres postgres  4096 Jul  3 16:03 .
drwx------. 19 postgres postgres  4096 Jul  3 16:01 ..
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1213
-rw-------.  1 postgres postgres 24576 Jul  3 16:01 1213_fsm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1213_vm
-rw-------.  1 postgres postgres     0 Jul  3 16:01 1214
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1232
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1233
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1260
-rw-------.  1 postgres postgres 24576 Jul  3 16:01 1260_fsm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1260_vm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1261
-rw-------.  1 postgres postgres 24576 Jul  3 16:01 1261_fsm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1261_vm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1262
-rw-------.  1 postgres postgres 24576 Jul  3 16:01 1262_fsm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 1262_vm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 2396
-rw-------.  1 postgres postgres 24576 Jul  3 16:01 2396_fsm
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 2396_vm
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2397
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2671
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2672
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2676
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2677
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2694
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2695
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2697
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 2698
-rw-------.  1 postgres postgres     0 Jul  3 16:01 2846
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 2847
-rw-------.  1 postgres postgres     0 Jul  3 16:01 2964
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 2965
-rw-------.  1 postgres postgres     0 Jul  3 16:01 2966
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 2967
-rw-------.  1 postgres postgres     0 Jul  3 16:01 3592
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 3593
-rw-------.  1 postgres postgres     0 Jul  3 16:01 4060
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 4061
-rw-------.  1 postgres postgres     0 Jul  3 16:01 4175
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 4176
-rw-------.  1 postgres postgres     0 Jul  3 16:01 4177
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 4178
-rw-------.  1 postgres postgres     0 Jul  3 16:01 4181
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 4182
-rw-------.  1 postgres postgres     0 Jul  3 16:01 4183
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 4184
-rw-------.  1 postgres postgres     0 Jul  3 16:01 4185
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 4186
-rw-------.  1 postgres postgres     0 Jul  3 16:01 6000
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6001
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6002
-rw-------.  1 postgres postgres     0 Jul  3 16:01 6100
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6114
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6115
-rw-------.  1 postgres postgres     0 Jul  3 16:01 6243
-rw-------.  1 postgres postgres     0 Jul  3 16:01 6244
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6245
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6246
-rw-------.  1 postgres postgres  8192 Jul  3 16:01 6247 
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 6302
-rw-------.  1 postgres postgres 16384 Jul  3 16:01 6303
-rw-------.  1 postgres postgres  8192 Jul  3 16:06 pg_control
-rw-------.  1 postgres postgres   524 Jul  3 16:01 pg_filenode.map
-rw-------.  1 postgres postgres 28724 Jul  3 16:03 pg_internal.init
[postgres@lxceftsgvdb01 ~]$

-- List of Files and Directories from Base Directory 

[postgres@lxceftsgvdb01 ~]$ ls -la /pgData/pgsql17/data/base
total 40
drwx------.  5 postgres postgres   33 Jul  3 16:01 .
drwx------. 19 postgres postgres 4096 Jul  3 16:01 ..
drwx------.  2 postgres postgres 8192 Jul  3 16:03 1
drwx------.  2 postgres postgres 8192 Jul  3 16:01 4
drwx------.  2 postgres postgres 8192 Jul  3 16:02 5
[postgres@lxceftsgvdb01 ~]$

1. The Global Directory (pg_global)

The global directory contains data that is shared across the entire database cluster.

  • Path: $PGDATA/global/
  • Scope: Cluster-wide.
  • Contents: It stores “Shared System Catalogs.” These are tables that contain information applicable to every database in the instance.
  • Key Files:
    • pg_database: Information about all databases in the cluster.
    • pg_authid: User roles and passwords (since a user can log into any database in the cluster).
    • pg_tablespace: Information about defined storage locations.
  • Identification: Objects in this directory always have an OID (Object Identifier), but they do not belong to a specific database ID.

Lists only actual shared/global catalog tables (no indexes, no TOAST tables) from the global directory

-- Let's look at inside postgres global directory (only actual tables, excluding indexes and TOAST)

[postgres@lxceftsgvdb01 ~]$ cat list_global_tables.sh
#!/bin/bash
cd $PGDATA
# Header
printf "%-8s | %-40s | %-10s | %-15s | %-10s\n" \
"OID" "OBJECT_NAME" "TABLEOID" "SCHEMA" "TABLESPACE"

printf -- "-----------------------------------------------------------------------------------------------\n"

# Loop through files in global directory
for i in $(find global -maxdepth 1 -type f | awk -F/ '{print $2}' | egrep '^[0-9]' | egrep -v 'fsm|vm')
do
    # Get object details from oid2name
    result=$(oid2name -x -S -q -o $i)

    # Parse fields
    oid=$(echo $result | awk '{print $1}')
    name=$(echo $result | awk '{print $2}')
    tableoid=$(echo $result | awk '{print $3}')
    schema=$(echo $result | awk '{print $4}')
    db=$(echo $result | awk '{print $5}')

    # Check relation type from pg_class
    relkind=$(psql -At -c "SELECT relkind FROM pg_class WHERE oid=$oid;" 2>/dev/null)

    # Show only actual tables (relkind = r)
    if [ "$relkind" = "r" ]; then
        printf "%-8s | %-40s | %-10s | %-15s | %-10s\n" \
        "$oid" "$name" "$tableoid" "$schema" "$db"
    fi
done
[postgres@lxceftsgvdb01 ~]$

[postgres@lxceftsgvdb01 ~]$ ./list_global_tables.sh
OID      | OBJECT_NAME                              | TABLEOID   | SCHEMA          | TABLESPACE
-----------------------------------------------------------------------------------------------
1262     | pg_database                              | 1262       | pg_catalog      | pg_global
2964     | pg_db_role_setting                       | 2964       | pg_catalog      | pg_global
1213     | pg_tablespace                            | 1213       | pg_catalog      | pg_global
1260     | pg_authid                                | 1260       | pg_catalog      | pg_global
1261     | pg_auth_members                          | 1261       | pg_catalog      | pg_global
1214     | pg_shdepend                              | 1214       | pg_catalog      | pg_global
2396     | pg_shdescription                         | 2396       | pg_catalog      | pg_global
6000     | pg_replication_origin                    | 6000       | pg_catalog      | pg_global
3592     | pg_shseclabel                            | 3592       | pg_catalog      | pg_global
6243     | pg_parameter_acl                         | 6243       | pg_catalog      | pg_global
6100     | pg_subscription                          | 6100       | pg_catalog      | pg_global
[postgres@pgdb02 ~]$

[postgres@lxceftsgvdb01 ~]$ tree /pgData/pgsql17/data/global
/pgData/pgsql17/data/global
├── 1213
├── 1213_fsm
├── 1213_vm
├── 1214
├── 1232
├── 1233
├── 1260
├── 1260_fsm
├── 1260_vm
├── 1261
├── 1261_fsm
├── 1261_vm
├── 1262
├── 1262_fsm
├── 1262_vm
├── 2396
├── 2396_fsm
├── 2396_vm
├── 2397
├── 2671
├── 2672
├── 2676
├── 2677
├── 2694
├── 2695
├── 2697
├── 2698
├── 2846
├── 2847
├── 2964
├── 2965
├── 2966
├── 2967
├── 3592
├── 3593
├── 4060
├── 4061
├── 4175
├── 4176
├── 4177
├── 4178
├── 4181
├── 4182
├── 4183
├── 4184
├── 4185
├── 4186
├── 6000
├── 6001
├── 6002
├── 6100
├── 6114
├── 6115
├── 6243
├── 6244
├── 6245
├── 6246
├── 6247
├── 6302
├── 6303
├── pg_control
├── pg_filenode.map
└── pg_internal.init

0 directories, 63 files
[postgres@lxceftsgvdb01 ~]$

2. The Base Directory (pg_base)

The base directory contains the actual user data and system catalogs that are private to each specific database.

  • Path: $PGDATA/base/
  • Scope: Database-specific.
  • Structure: Inside base, there is a subdirectory for every database in the cluster, named after the database’s OID (e.g., $PGDATA/base/16384/).
  • Contents:
    • User Tables and Indexes: The actual data you insert into your tables.
    • Local System Catalogs: Tables like pg_class, pg_attribute, and pg_type which describe the structure of that specific database.
  • Identification: If you want to find where a specific table is stored, you look in base/[Database OID]/[Table Filenode]
[postgres@pgdb02 ~]$ psql -c "SELECT oid, datname FROM pg_database order by oid;"
 oid |  datname
-----+-----------
   1 | template1
   4 | template0
   5 | postgres
(3 rows)

[postgres@pgdb02 ~]$
[postgres@lxceftsgvdb01 ~]$ ls /pgData/pgsql17/data/base | sort -n
1  <---- template1
4  <---- template0
5  <---- postgres
[postgres@pgdb02 ~]$

-- Let's look at inside postgres Base directory (only actual tables, excluding indexes and TOAST)

[postgres@lxceftsgvdb01 ~]$ cat list_base_tables.sh
#!/bin/bash

export PGHOME=/usr/pgsql-17
export PGDATA=/pgData/pgsql17/data
export PATH=$PGHOME/bin:$PATH

DBNAME="postgres"

# Get database OID
DBOID=$(psql -At -d $DBNAME -c "SELECT oid FROM pg_database WHERE datname='$DBNAME'")

# Header
printf "%-8s | %-40s | %-10s | %-15s | %-10s\n" \
"OID" "OBJECT_NAME" "TABLEOID" "SCHEMA" "Tablespace"

printf -- "-----------------------------------------------------------------------------------------------\n"

# Use absolute path ($PGDATA/base/)
for i in $(find $PGDATA/base/$DBOID -maxdepth 1 -type f | awk -F/ '{print $NF}' | egrep '^[0-9]' | egrep -v 'fsm|vm')
do
    # Get object details
    result=$(oid2name -d $DBNAME -x -q -o $i)

    # Parse fields
    oid=$(echo "$result" | awk '{print $1}')
    name=$(echo "$result" | awk '{print $2}')
    tableoid=$(echo "$result" | awk '{print $3}')
    schema=$(echo "$result" | awk '{print $4}')
    db=$(echo "$result" | awk '{print $5}')

    # Check relation type
    relkind=$(psql -At -d $DBNAME -c "SELECT relkind FROM pg_class WHERE oid=$oid;" 2>/dev/null)

    # Show only actual tables
    if [ "$relkind" = "r" ]; then
        printf "%-8s | %-40s | %-10s | %-15s | %-10s\n" \
        "$oid" "$name" "$tableoid" "$schema" "$db"
    fi
done
[postgres@lxceftsgvdb01 ~]$

[postgres@lxceftsgvdb01 ~]$ ./list_base_tables.sh

OID      | OBJECT_NAME                              | TABLEOID   | SCHEMA          | TABLESPACE
-----------------------------------------------------------------------------------------------
1255     | pg_proc                                  | 1255       | pg_catalog      | pg_default
1247     | pg_type                                  | 1247       | pg_catalog      | pg_default
1249     | pg_attribute                             | 1249       | pg_catalog      | pg_default
1259     | pg_class                                 | 1259       | pg_catalog      | pg_default
2604     | pg_attrdef                               | 2604       | pg_catalog      | pg_default
2606     | pg_constraint                            | 2606       | pg_catalog      | pg_default
2611     | pg_inherits                              | 2611       | pg_catalog      | pg_default
2610     | pg_index                                 | 2610       | pg_catalog      | pg_default
2617     | pg_operator                              | 2617       | pg_catalog      | pg_default
2753     | pg_opfamily                              | 2753       | pg_catalog      | pg_default
2616     | pg_opclass                               | 2616       | pg_catalog      | pg_default
2601     | pg_am                                    | 2601       | pg_catalog      | pg_default
2602     | pg_amop                                  | 2602       | pg_catalog      | pg_default
2603     | pg_amproc                                | 2603       | pg_catalog      | pg_default
2612     | pg_language                              | 2612       | pg_catalog      | pg_default
2995     | pg_largeobject_metadata                  | 2995       | pg_catalog      | pg_default
2613     | pg_largeobject                           | 2613       | pg_catalog      | pg_default
2600     | pg_aggregate                             | 2600       | pg_catalog      | pg_default
2619     | pg_statistic                             | 2619       | pg_catalog      | pg_default
3381     | pg_statistic_ext                         | 3381       | pg_catalog      | pg_default
3429     | pg_statistic_ext_data                    | 3429       | pg_catalog      | pg_default
2618     | pg_rewrite                               | 2618       | pg_catalog      | pg_default
2620     | pg_trigger                               | 2620       | pg_catalog      | pg_default
3466     | pg_event_trigger                         | 3466       | pg_catalog      | pg_default
2609     | pg_description                           | 2609       | pg_catalog      | pg_default
2605     | pg_cast                                  | 2605       | pg_catalog      | pg_default
3501     | pg_enum                                  | 3501       | pg_catalog      | pg_default
2615     | pg_namespace                             | 2615       | pg_catalog      | pg_default
2607     | pg_conversion                            | 2607       | pg_catalog      | pg_default
2608     | pg_depend                                | 2608       | pg_catalog      | pg_default
3602     | pg_ts_config                             | 3602       | pg_catalog      | pg_default
3603     | pg_ts_config_map                         | 3603       | pg_catalog      | pg_default
3600     | pg_ts_dict                               | 3600       | pg_catalog      | pg_default
3601     | pg_ts_parser                             | 3601       | pg_catalog      | pg_default
3764     | pg_ts_template                           | 3764       | pg_catalog      | pg_default
3079     | pg_extension                             | 3079       | pg_catalog      | pg_default
2328     | pg_foreign_data_wrapper                  | 2328       | pg_catalog      | pg_default
1417     | pg_foreign_server                        | 1417       | pg_catalog      | pg_default
1418     | pg_user_mapping                          | 1418       | pg_catalog      | pg_default
3118     | pg_foreign_table                         | 3118       | pg_catalog      | pg_default
3256     | pg_policy                                | 3256       | pg_catalog      | pg_default
826      | pg_default_acl                           | 826        | pg_catalog      | pg_default
3394     | pg_init_privs                            | 3394       | pg_catalog      | pg_default
3596     | pg_seclabel                              | 3596       | pg_catalog      | pg_default
3456     | pg_collation                             | 3456       | pg_catalog      | pg_default
3350     | pg_partitioned_table                     | 3350       | pg_catalog      | pg_default
3541     | pg_range                                 | 3541       | pg_catalog      | pg_default
3576     | pg_transform                             | 3576       | pg_catalog      | pg_default
2224     | pg_sequence                              | 2224       | pg_catalog      | pg_default
6104     | pg_publication                           | 6104       | pg_catalog      | pg_default
6237     | pg_publication_namespace                 | 6237       | pg_catalog      | pg_default
6106     | pg_publication_rel                       | 6106       | pg_catalog      | pg_default
6102     | pg_subscription_rel                      | 6102       | pg_catalog      | pg_default
14382    | sql_features                             | 14382      | information_schema | pg_default
14387    | sql_implementation_info                  | 14387      | information_schema | pg_default
14392    | sql_parts                                | 14392      | information_schema | pg_default
14397    | sql_sizing                               | 14397      | information_schema | pg_default
[postgres@lxceftsgvdb01 ~]$

-- Let's look at inside postgres Base directory (Complete List)

[postgres@lxceftsgvdb01 ~]$ tree /pgData/pgsql17/data/base/5
/pgData/pgsql17/data/base/5
├── 112
├── 113
├── 1247
├── 1247_fsm
├── 1247_vm
├── 1249
├── 1249_fsm
├── 1249_vm
├── 1255
├── 1255_fsm
├── 1255_vm
├── 1259
├── 1259_fsm
├── 1259_vm
├── 1417
├── 1418
├── 14382
├── 14382_fsm
├── 14382_vm
├── 14385
├── 14386
├── 14387
├── 14387_fsm
├── 14387_vm
├── 14390
├── 14391
├── 14392
├── 14392_fsm
├── 14392_vm
├── 14395
├── 14396
├── 14397
├── 14397_fsm
├── 14397_vm
├── 14400
├── 14401
├── 174
├── 175
├── 2187
├── 2224
├── 2228
├── 2328
├── 2336
├── 2337
├── 2579
├── 2600
├── 2600_fsm
├── 2600_vm
├── 2601
├── 2601_fsm
├── 2601_vm
├── 2602
├── 2602_fsm
├── 2602_vm
├── 2603
├── 2603_fsm
├── 2603_vm
├── 2604
├── 2605
├── 2605_fsm
├── 2605_vm
├── 2606
├── 2606_fsm
├── 2606_vm
├── 2607
├── 2607_fsm
├── 2607_vm
├── 2608
├── 2608_fsm
├── 2608_vm
├── 2609
├── 2609_fsm
├── 2609_vm
├── 2610
├── 2610_fsm
├── 2610_vm
├── 2611
├── 2612
├── 2612_fsm
├── 2612_vm
├── 2613
├── 2615
├── 2615_fsm
├── 2615_vm
├── 2616
├── 2616_fsm
├── 2616_vm
├── 2617
├── 2617_fsm
├── 2617_vm
├── 2618
├── 2618_fsm
├── 2618_vm
├── 2619
├── 2619_fsm
├── 2619_vm
├── 2620
├── 2650
├── 2651
├── 2652
├── 2653
├── 2654
├── 2655
├── 2656
├── 2657
├── 2658
├── 2659
├── 2660
├── 2661
├── 2662
├── 2663
├── 2664
├── 2665
├── 2666
├── 2667
├── 2668
├── 2669
├── 2670
├── 2673
├── 2674
├── 2675
├── 2678
├── 2679
├── 2680
├── 2681
├── 2682
├── 2683
├── 2684
├── 2685
├── 2686
├── 2687
├── 2688
├── 2689
├── 2690
├── 2691
├── 2692
├── 2693
├── 2696
├── 2699
├── 2701
├── 2702
├── 2703
├── 2704
├── 2753
├── 2753_fsm
├── 2753_vm
├── 2754
├── 2755
├── 2756
├── 2757
├── 2830
├── 2831
├── 2832
├── 2833
├── 2834
├── 2835
├── 2836
├── 2836_fsm
├── 2836_vm
├── 2837
├── 2838
├── 2838_fsm
├── 2838_vm
├── 2839
├── 2840
├── 2840_fsm
├── 2840_vm
├── 2841
├── 2995
├── 2996
├── 3079
├── 3079_fsm
├── 3079_vm
├── 3080
├── 3081
├── 3085
├── 3118
├── 3119
├── 3164
├── 3256
├── 3257
├── 3258
├── 3350
├── 3351
├── 3379
├── 3380
├── 3381
├── 3394
├── 3394_fsm
├── 3394_vm
├── 3395
├── 3429
├── 3430
├── 3431
├── 3433
├── 3439
├── 3440
├── 3455
├── 3456
├── 3456_fsm
├── 3456_vm
├── 3466
├── 3467
├── 3468
├── 3501
├── 3502
├── 3503
├── 3534
├── 3541
├── 3541_fsm
├── 3541_vm
├── 3542
├── 3574
├── 3575
├── 3576
├── 3596
├── 3597
├── 3598
├── 3599
├── 3600
├── 3600_fsm
├── 3600_vm
├── 3601
├── 3601_fsm
├── 3601_vm
├── 3602
├── 3602_fsm
├── 3602_vm
├── 3603
├── 3603_fsm
├── 3603_vm
├── 3604
├── 3605
├── 3606
├── 3607
├── 3608
├── 3609
├── 3712
├── 3764
├── 3764_fsm
├── 3764_vm
├── 3766
├── 3767
├── 3997
├── 4143
├── 4144
├── 4145
├── 4146
├── 4147
├── 4148
├── 4149
├── 4150
├── 4151
├── 4152
├── 4153
├── 4154
├── 4155
├── 4156
├── 4157
├── 4158
├── 4159
├── 4160
├── 4163
├── 4164
├── 4165
├── 4166
├── 4167
├── 4168
├── 4169
├── 4170
├── 4171
├── 4172
├── 4173
├── 4174
├── 5002
├── 548
├── 549
├── 6102
├── 6104
├── 6106
├── 6110
├── 6111
├── 6112
├── 6113
├── 6116
├── 6117
├── 6175
├── 6176
├── 6228
├── 6229
├── 6237
├── 6238
├── 6239
├── 826
├── 827
├── 828
├── pg_filenode.map
├── pg_internal.init
└── PG_VERSION

0 directories, 299 files
[postgres@lxceftsgvdb01 ~]$
Caution: Your use of any information or materials on this website is entirely at your own risk. It is provided for educational purposes only. It has been tested internally, however, we do not guarantee that it will work for you. Ensure that you run it in your test environment before using.Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

Create a Second PostgreSQL Instance on the Same Linux Server

PostgreSQL, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Create a Second PostgreSQL Instance on the Same Linux Server

Table of Contents

0. Verify existing setup

[postgres@pgdb02 ~]$ ps -ef | grep postgres
root        3641    3561  0 16:57 pts/1    00:00:00 su - postgres
postgres    3642    3641  0 16:57 pts/1    00:00:00 -bash
postgres    3711       1  0 17:03 ?        00:00:00 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4
postgres    3712    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: checkpointer
postgres    3713    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: background writer
postgres    3715    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: walwriter
postgres    3716    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: autovacuum launcher
postgres    3717    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: logical replication launcher
postgres    3731    3642  0 17:03 pts/1    00:00:00 psql
postgres    3732    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: postgres postgres [local] idle
root        3748    3164  0 17:09 pts/0    00:00:00 su - postgres
postgres    3749    3748  0 17:09 pts/0    00:00:00 -bash
postgres    3911    3749  0 17:59 pts/0    00:00:00 ps -ef
postgres    3912    3749  0 17:59 pts/0    00:00:00 grep --color=auto postgres
[postgres@pgdb02 ~]$

1. Create new directories

[root@pgdb02 ~]# mkdir -p /pgData/pgsql/17.4/dev
[root@pgdb02 ~]# mkdir -p /pgWal/pgsql/17.4/dev
[root@pgdb02 ~]# chown -R postgres:postgres /pgData /pgWal
[root@pgdb02 ~]#

2. Initialize second cluster

# As postgres user 

[postgres@pgdb02 ~]$ /pgBin/pgsql/17.4/bin/initdb -D /pgData/pgsql/17.4/dev --waldir=/pgWal/pgsql/17.4/dev --wal-segsize=128
The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_SG.UTF-8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /pgData/pgsql/17.4/dev ... ok
fixing permissions on existing directory /pgWal/pgsql/17.4/dev ... ok
creating subdirectories ... ok
selecting dynamic shared memory implementation ... posix
selecting default "max_connections" ... 100
selecting default "shared_buffers" ... 128MB
selecting default time zone ... Asia/Singapore
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... ok
syncing data to disk ... ok

initdb: warning: enabling "trust" authentication for local connections
initdb: hint: You can change this by editing pg_hba.conf or using the option -A, or --auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

    /pgBin/pgsql/17.4/bin/pg_ctl -D /pgData/pgsql/17.4/dev -l logfile start

[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ ls -ld /pgData/pgsql/17.4/dev
drwx------. 18 postgres postgres 4096 Jun 20 18:03 /pgData/pgsql/17.4/dev
[postgres@pgdb02 ~]$
[postgres@pgdb02 ~]$ ls -ltr /pgData/pgsql/17.4/dev
total 56
lrwxrwxrwx. 1 postgres postgres    21 Jun 20 18:03 pg_wal -> /pgWal/pgsql/17.4/dev
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_commit_ts
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_dynshmem
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_twophase
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_tblspc
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_stat_tmp
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_snapshots
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_serial
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_replslot
drwx------. 2 postgres postgres     6 Jun 20 18:03 pg_notify
drwx------. 4 postgres postgres    36 Jun 20 18:03 pg_multixact
-rw-------. 1 postgres postgres     3 Jun 20 18:03 PG_VERSION
-rw-------. 1 postgres postgres 30718 Jun 20 18:03 postgresql.conf
-rw-------. 1 postgres postgres    88 Jun 20 18:03 postgresql.auto.conf
-rw-------. 1 postgres postgres  5711 Jun 20 18:03 pg_hba.conf
-rw-------. 1 postgres postgres  2640 Jun 20 18:03 pg_ident.conf
drwx------. 2 postgres postgres    18 Jun 20 18:03 pg_xact
drwx------. 2 postgres postgres    18 Jun 20 18:03 pg_subtrans
drwx------. 2 postgres postgres  4096 Jun 20 18:03 global
drwx------. 5 postgres postgres    33 Jun 20 18:03 base
drwx------. 4 postgres postgres    68 Jun 20 18:03 pg_logical
drwx------. 2 postgres postgres    25 Jun 20 18:03 pg_stat
[postgres@pgdb02 ~]$

**** we can see here 700 permission set by initdb command.

3. Edit second instance config

[postgres@pgdb02 ~]$ egrep "^(#)?(port|cluster_name)" /pgData/pgsql/17.4/dev/postgresql.conf
#port = 5432                            # (change requires restart)
#cluster_name = ''                      # added to process titles if nonempty
[postgres@pgdb02 ~]$


[postgres@pgdb02 ~]$ cp /pgData/pgsql/17.4/dev/postgresql.conf /pgData/pgsql/17.4/dev/postgresql.conf.bkp
[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ sed -i "s/^#port = 5432.*/port = 5433/" /pgData/pgsql/17.4/dev/postgresql.conf
[postgres@pgdb02 ~]$ sed -i "s/^#cluster_name = ''.*/cluster_name = 'PGDB_UAT'/" /pgData/pgsql/17.4/dev/postgresql.conf
[postgres@pgdb02 ~]$
[postgres@pgdb02 ~]$ egrep "^(#)?(port|cluster_name)" /pgData/pgsql/17.4/dev/postgresql.conf
port = 5433
cluster_name = 'PGDB_UAT'
[postgres@pgdb02 ~]$

4. Start PostgreSQL Service

[postgres@pgdb02 ~]$ /pgBin/pgsql/17.4/bin/pg_ctl -D /pgData/pgsql/17.4/dev -l logfile start
waiting for server to start.... done
server started
[postgres@pgdb02 ~]$

5. Connect to second instance

[postgres@pgdb02 ~]$ psql -p 5433
psql (17.4)
Type "help" for help.

postgres=# SHOW port;
 port
------
 5433  <-----------
(1 row)

postgres=# SHOW cluster_name;
 cluster_name
--------------
 PGDB_UAT  <---------------
(1 row)

postgres=#\q

[postgres@pgdb02 ~]$ pg_ctl stop -D /pgData/pgsql/17.4/dev
waiting for server to shut down.... done
server stopped
[postgres@pgdb02 ~]$

6. Create second systemd service

[root@pgdb02 ~]# cp /etc/systemd/system/postgresql-17.service /etc/systemd/system/postgresql-17-dev.service
[root@pgdb02 ~]#
[root@pgdb02 ~]# grep -i Environment=PGDATA /etc/systemd/system/postgresql-17-dev.service
Environment=PGDATA=/pgData/pgsql/17.4
[root@pgdb02 ~]#

[root@pgdb02 ~]# sed -i 's|Environment=PGDATA=/pgData/pgsql/17.4|Environment=PGDATA=/pgData/pgsql/17.4/dev|' /etc/systemd/system/postgresql-17-dev.service
[root@pgdb02 ~]# grep -i Environment=PGDATA /etc/systemd/system/postgresql-17-dev.service
Environment=PGDATA=/pgData/pgsql/17.4/dev
[root@pgdb02 ~]#

[root@pgdb02 ~]# systemctl daemon-reload
[root@pgdb02 ~]# systemctl start postgresql-17-dev
[root@pgdb02 ~]# systemctl enable postgresql-17-dev
Created symlink /etc/systemd/system/multi-user.target.wants/postgresql-17-dev.service → /etc/systemd/system/postgresql-17-dev.service.
[root@pgdb02 ~]#
[root@pgdb02 ~]# systemctl status postgresql-17-dev
● postgresql-17-dev.service - PostgreSQL 17 Database Server
     Loaded: loaded (/etc/systemd/system/postgresql-17-dev.service; enabled; preset: disabled)
     Active: active (running) since Sat 2026-06-20 18:25:39 +08; 12s ago
       Docs: https://www.postgresql.org/docs/17/
   Main PID: 4106 (postgres)
      Tasks: 6 (limit: 15700)
     Memory: 15.2M
        CPU: 62ms
     CGroup: /system.slice/postgresql-17-dev.service
             ├─4106 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4/dev
             ├─4107 "postgres: PGDB_UAT: checkpointer "
             ├─4108 "postgres: PGDB_UAT: background writer "
             ├─4110 "postgres: PGDB_UAT: walwriter "
             ├─4111 "postgres: PGDB_UAT: autovacuum launcher "
             └─4112 "postgres: PGDB_UAT: logical replication launcher "

Jun 20 18:25:39 pgdb02 systemd[1]: Starting PostgreSQL 17 Database Server...
Jun 20 18:25:39 pgdb02 pg_ctl[4103]: waiting for server to start.... done
Jun 20 18:25:39 pgdb02 pg_ctl[4103]: server started
Jun 20 18:25:39 pgdb02 systemd[1]: Started PostgreSQL 17 Database Server.
[root@pgdb02 ~]#

7. Verify instances

[postgres@pgdb02 ~]$ ps -ef | grep postgres
postgres    3711       1  0 17:03 ?        00:00:00 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4
postgres    3712    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: checkpointer
postgres    3713    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: background writer
postgres    3715    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: walwriter
postgres    3716    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: autovacuum launcher
postgres    3717    3711  0 17:03 ?        00:00:00 postgres: PGDB_SIT: logical replication launcher
root        3748    3164  0 17:09 pts/0    00:00:00 su - postgres
postgres    3749    3748  0 17:09 pts/0    00:00:00 -bash
postgres    4106       1  0 18:25 ?        00:00:00 /pgBin/pgsql/17.4/bin/postgres -D /pgData/pgsql/17.4/dev
postgres    4107    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: checkpointer
postgres    4108    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: background writer
postgres    4110    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: walwriter
postgres    4111    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: autovacuum launcher
postgres    4112    4106  0 18:25 ?        00:00:00 postgres: PGDB_UAT: logical replication launcher
postgres    4157    3749 99 18:26 pts/0    00:00:00 ps -ef
postgres    4158    3749  0 18:26 pts/0    00:00:00 grep --color=auto postgres
[postgres@pgdb02 ~]$

[postgres@pgdb02 ~]$ ss -tulpn | grep 543
tcp   LISTEN 0      200        127.0.0.1:5433       0.0.0.0:*    users:(("postgres",pid=4106,fd=7))
tcp   LISTEN 0      200        127.0.0.1:5432       0.0.0.0:*    users:(("postgres",pid=3711,fd=7))
tcp   LISTEN 0      200            [::1]:5432          [::]:*    users:(("postgres",pid=3711,fd=6))
tcp   LISTEN 0      200            [::1]:5433          [::]:*    users:(("postgres",pid=4106,fd=6))
[postgres@pgdb02 ~]$

Caution: Your use of any information or materials on this website is entirely at your own risk. It is provided for educational purposes only. It has been tested internally, however, we do not guarantee that it will work for you. Ensure that you run it in your test environment before using.

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

Uninstall PostgreSQL 17 on Linux (RPM Method)

PostgreSQL, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Uninstall PostgreSQL 17 on Linux (Installed Using RPM Method)

Table of Contents

0. Important Caution Before Proceeding

** Before uninstalling PostgreSQL PostgreSQL 17, first take a logical or physical backup. **

If PostgreSQL was installed using RPM packages, removing the package does not automatically remove:

Database files
WAL files
Backup directories
Custom configuration files

1. Check Installed PostgreSQL RPM Packages

[root@pgdb02 ~]# rpm -qa | grep postgres
postgresql17-libs-17.6-1PGDG.rhel9.x86_64
postgresql17-17.6-1PGDG.rhel9.x86_64
postgresql17-server-17.6-1PGDG.rhel9.x86_64
postgresql17-contrib-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]#

2. Stop PostgreSQL Service

[root@pgdb02 ~]# systemctl stop postgresql-17
[root@pgdb02 ~]# systemctl status postgresql-17
○ postgresql-17.service - PostgreSQL 17 database server
Loaded: loaded (/usr/lib/systemd/system/postgresql-17.service; enabled; preset: disabled)
Active: inactive (dead)
Docs: https://www.postgresql.org/docs/17/static/
[root@pgdb02 ~]#

3. Disable PostgreSQL Service

[root@pgdb02 ~]# systemctl disable postgresql-17
Removed "/etc/systemd/system/multi-user.target.wants/postgresql-17.service".
[root@pgdb02 ~]#

4. Remove and Verify PostgreSQL RPM Packages

WARNING: This permanently deletes all binaries, libraries, and data. Ensure your data is backed up before this step.

[root@pgdb02 ~]# rpm -qa | grep postgres
postgresql17-libs-17.6-1PGDG.rhel9.x86_64
postgresql17-17.6-1PGDG.rhel9.x86_64
postgresql17-server-17.6-1PGDG.rhel9.x86_64
postgresql17-contrib-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]#
[root@pgdb02 ~]# rpm -e postgresql17-contrib-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]# rpm -e postgresql17-server-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]# rpm -e postgresql17-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]# rpm -e postgresql17-libs-17.6-1PGDG.rhel9.x86_64
[root@pgdb02 ~]#

5. Verify Packages Are Removed

[root@pgdb02 ~]# rpm -qa | grep postgres
[root@pgdb02 ~]#

6. Remove PostgreSQL System User (Optional)

[root@pgdb02 ~]# id postgres
uid=26(postgres) gid=26(postgres) groups=26(postgres)
[root@pgdb02 ~]# userdel postgres
[root@pgdb02 ~]#
[root@pgdb02 ~]# groupdel postgres
groupdel: group 'postgres' does not exist
[root@pgdb02 ~]#
[root@pgdb02 ~]# id postgres
id: ‘postgres’: no such user
[root@pgdb02 ~]#

7. Remove PostgreSQL Configuration Files

# It's already removed in step no. 3

[root@pgdb02 ~]# ls -l /usr/lib/systemd/system/postgresql-17.service
ls: cannot access '/usr/lib/systemd/system/postgresql-17.service': No such file or directory
[root@pgdb02 ~]# 
[root@pgdb02 ~]# ls -l /etc/systemd/system/postgresql-17.service
-rw-r--r--. 1 root root 588 Jun 19 21:20 /etc/systemd/system/postgresql-17.service
[root@pgdb02 ~]#
[root@pgdb02 ~]# rm -f /etc/systemd/system/postgresql-17.service
[root@pgdb02 ~]#

8. Verify Complete Removal

[root@pgdb02 ~]# id postgres
id: ‘postgres’: no such user
[root@pgdb02 ~]#
[root@pgdb02 ~]# rpm -qa | grep postgres
[root@pgdb02 ~]#
[root@pgdb02 ~]# systemctl status postgresql-17
Unit postgresql-17.service could not be found.
[root@pgdb02 ~]#

Caution: Your use of any information or materials on this website is entirely at your own risk. It is provided for educational purposes only. It has been tested internally, however, we do not guarantee that it will work for you. Ensure that you run it in your test environment before using.

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

PostgreSQL

Uncategorized, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

PostgreSQL DBA Step by Step Learning

#PostgreSQL DBA Topics
1How to Install PostgreSQL ON Linux?
2How to Install PostgreSQL on Linux 7 using source code?
3How to START/STOP PostgreSQL ON Linux?
4How to Create Database in PostgreSQL?
5PostgreSQL User Management
6PostgreSQL pg_hba.conf Guide
7PostgreSQL Change Data Directory
8Understanding WAL Files in PostgreSQL – For Oracle DBAs
9Change PostgreSQL WAL Directory Path (pg_wal)
10Enable Archive Mode in PostgreSQL 17
11How to Disable ARCHIVELOG Mode
12PostgreSQL Tablespace Management
13PostgreSQL pg_dump and pg_restore Guide
14PostgreSQL Backup and Restore Using pg_dumpall and psql
15pg_basebackup – Backup, Restore, and Recovery
16Backup & Restore PostgreSQL DB Cluster to Another Host (No Archive Mode)
17Backup & Restore PostgreSQL DB Cluster on Same Host
18Restore PostgreSQL to New Host using pg_basebackup + WAL Archives
19PostgreSQL PITR – Point in Time Recovery
20Configure Streaming Replication in PostgreSQL
21Manual Failover in PostgreSQL Streaming Replication
22Convert Asynchronous Replication to Synchronous Replication

 

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

Backup and Restore on Same Host Using pg_basebackup

PostgreSQL, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

How to Backup and Restore PostgreSQL DB Cluster on the Same Host Using pg_basebackup

Table of Contents

1. Environment
2. Verify Existing DB Setup
3. Pre-requisites
4. Take Backup
5. Prepare & Restore
     5.1 Stop PostgreSQL and Clean Directories
     5.2 Remove all from Data & WAL directories
     5.3 Restore Data and WAL
         A. Copy Backup files to $PGDATA
         B. Copy WAL files from $PGDATA/pg_wal to /pgWal/pgsql17/wal/
         C. Remove the existing $PGDATA/pg_wal directory
         D. Create a symbolic link pointing $PGDATA/pg_wal to a separate WAL directory
         E. Set Permissions
6. Start PostgreSQL
7. Final Verification

1. Environment

ASPECTEnv
Hostnamelxicbpgdsgv01
IP Address192.168.2.51
OSRHEL 9
DB VersionPostgreSQL v17.6
Archive modearchive_mode=off
pgData/pgData/pgsql17/data
WAL Directory/pgWal/pgsql17/wal
Tablespacepg_default
DatabasesDELL, ORCL

2. Verify Existing DB Setup

[postgres@lxicbpgdsgv01 ~]$ psql
psql (17.6)
Type "help" for help.

postgres=# \l+
                                                                                       List of databases
   Name    |  Owner   | Encoding | Locale Provider |   Collate   |    Ctype    | Locale | ICU Rules |   Access privileges   |  Size   | Tablespace |                Description
-----------+----------+----------+-----------------+-------------+-------------+--------+-----------+-----------------------+---------+------------+--------------------------------------------
 dell      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7763 kB | pg_default |
 orcl      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7907 kB | pg_default |
 postgres  | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 492 MB  | pg_default | default administrative connection database
 template0 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7545 kB | pg_default | unmodifiable empty database
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
 template1 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7723 kB | pg_default | default template for new databases
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
(5 rows)

postgres=# \db
       List of tablespaces
    Name    |  Owner   | Location
------------+----------+----------
 pg_default | postgres |
 pg_global  | postgres |
(2 rows)

postgres=# \c dell
You are now connected to database "dell" as user "postgres".
dell=# select * from test.emp;
 name | designation | project | company
------+-------------+---------+---------
 Sugi | DBA         | Jetstar | iGATE
 Teja | DBA         | RCM     | iGATE
 RAJ  | DBA         | RCM     | iGATE
(3 rows)

dell=#

3. Pre-requisites

  • Verify postgresql.conf
postgres=# SHOW wal_level;
 wal_level
-----------
 replica <----
(1 row)

postgres=#
postgres=# SHOW max_wal_senders;
 max_wal_senders
-----------------
 10
(1 row)

postgres=# SHOW archive_mode;
 archive_mode
--------------
 off
(1 row)

postgres=#
  • Verify pg_hba.conf
# TYPE  DATABASE        USER            ADDRESS             METHOD
# Local connections for replication (for pg_basebackup run locally)
local   replication     all                                 trust

# Remote connections for replication (for pg_basebackup run remotely)
#host    replication     repl_user       192.168.2.52/32     scram-sha-256
  • Verify user permissions:REPLICATION or SUPERUSER required
postgres=# \du
                             List of roles
 Role name |                         Attributes
-----------+------------------------------------------------------------
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS

postgres=#
  • Verify free space for backup
[postgres@lxicbpgdsgv01 ~]$ du -sh /pgData/pgsql17/data/
524M    /pgData/pgsql17/data/
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ du -sh /pgWal/pgsql17/wal/
801M    /pgWal/pgsql17/wal/
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ df -h /pgBackup/
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdd1       100G  746M  100G   1% /pgBackup <----
[postgres@lxicbpgdsgv01 ~]$ mkdir -p /pgBackup/pgsql17/backup/basebackup_10OCT2025
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ mkdir -p /pgBackup/pgsql17/backup/log/
[postgres@lxicbpgdsgv01 ~]$

4. Take Backup

[postgres@lxicbpgdsgv01 ~]$ ls -ltrh /pgWal/pgsql17/wal | wc -l
53 <---- 
[postgres@lxicbpgdsgv01 ~]$

pg_basebackup does not include all files from the pg_wal directory in the backup. Instead, it selectively includes only the WAL files required to make the base backup consistent at the point in time the backup was taken.

-- If you want to store the base backup and WAL files in separate backup directories. 

nohup pg_basebackup -U postgres -D /pgBackup/pgsql17/backup/basebackup_10OCT2025 --waldir=/pgBackup/pgsql17/backup/wal_backup -Fp -Xs -P -v > /pgBackup/pgsql17/backup/log/basebackup_10OCT2025.log 2>&1 &

The --waldir option in pg_basebackup is supported only when using the plain format (-Fp), not with the tar format (-Ft).

If we want symlinks preserved → use (both -Fp & --waldir use together) -Fp --waldir=/pgWal/pgsql17/wal

-- OR --

The directory mush be empty: /pgBackup/pgsql17/backup/basebackup_10OCT2025

[postgres@lxicbpgdsgv01 ~]$ nohup pg_basebackup -U postgres -D /pgBackup/pgsql17/backup/basebackup_10OCT2025 -Fp -Xs -P -v > /pgBackup/pgsql17/backup/log/basebackup_10OCT2025.log 2>&1 &
[1] 4973
[postgres@lxicbpgdsgv01 ~]$

[postgres@lxicbpgdsgv01 ~]$ cat /pgBackup/pgsql17/backup/log/basebackup_10OCT2025.log
nohup: ignoring input
pg_basebackup: initiating base backup, waiting for checkpoint to complete
pg_basebackup: checkpoint completed
pg_basebackup: write-ahead log start point: 0/85000028 on timeline 1
pg_basebackup: starting background WAL receiver
pg_basebackup: created temporary replication slot "pg_basebackup_4975"
279413/536037 kB (52%), 0/1 tablespace (...asebackup_10OCT2025/base/5/16533)
536047/536047 kB (100%), 0/1 tablespace (...ckup_10OCT2025/global/pg_control)
536047/536047 kB (100%), 1/1 tablespace
pg_basebackup: write-ahead log end point: 0/85000158
pg_basebackup: waiting for background process to finish streaming ...
pg_basebackup: syncing data to disk ...
pg_basebackup: renaming backup_manifest.tmp to backup_manifest
pg_basebackup: base backup completed  <-----
[postgres@lxicbpgdsgv01 ~]$

5. Prepare & Restore

5.1 Stop PostgreSQL and Clean Directories

[root@lxicbpgdsgv01 ~]# systemctl stop postgresql-17.service
[root@lxicbpgdsgv01 ~]# 
[root@lxicbpgdsgv01 ~]# ps -ef | grep postgres
root        5057    3151  0 18:57 pts/0    00:00:00 grep --color=auto postgres
[root@lxicbpgdsgv01 ~]#

5.2 Remove all from Data & WAL directories

-- Remove all from PGDATA directory

[root@lxicbpgdsgv01 ~]# rm -rf /pgData/pgsql17/data/*
[root@lxicbpgdsgv01 ~]# ls -ltr /pgData/pgsql17/data/
total 0
[root@lxicbpgdsgv01 ~]#

-- Remove all from WAL directory 

[root@lxicbpgdsgv01 ~]# rm -rf /pgWal/pgsql17/wal/*
[root@lxicbpgdsgv01 ~]# ls -ltr /pgWal/pgsql17/wal/
total 0
[root@lxicbpgdsgv01 ~]#

5.3 Restore Data and WAL

A. Copy Backup files to $PGDATA
Since we did not use the -Fp format with the --waldir option, all required WAL files will be included in the backup under the default path: PGDATA/pg_wal.

[postgres@lxicbpgdsgv01 ~]$ ls -ltr /pgData/pgsql17/data/
total 0
[postgres@lxicbpgdsgv01 ~]$ cd /pgBackup/pgsql17/backup/basebackup_10OCT2025/
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$ cp -Rp * /pgData/pgsql17/data/
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$ ls -ltr /pgData/pgsql17/data/
total 296
-rw-------. 1 postgres postgres    227 Oct 10 18:41 backup_label
drwx------. 4 postgres postgres     77 Oct 10 18:41 pg_wal
drwx------. 7 postgres postgres     59 Oct 10 18:41 base
drwx------. 4 postgres postgres     68 Oct 10 18:41 pg_logical
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_dynshmem
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_commit_ts
drwx------. 2 postgres postgres    110 Oct 10 18:41 log
-rw-------. 1 postgres postgres   1169 Oct 10 18:41 postgresql.conf.bkp_10sep2025
-rw-------. 1 postgres postgres  30702 Oct 10 18:41 postgresql.conf.bkp
-rw-------. 1 postgres postgres     88 Oct 10 18:41 postgresql.auto.conf
drwx------. 2 postgres postgres     18 Oct 10 18:41 pg_xact
-rw-------. 1 postgres postgres      3 Oct 10 18:41 PG_VERSION
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_twophase
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_tblspc
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_subtrans
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_stat_tmp
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_stat
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_snapshots
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_serial
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_replslot
drwx------. 2 postgres postgres      6 Oct 10 18:41 pg_notify
drwx------. 4 postgres postgres     36 Oct 10 18:41 pg_multixact
-rw-------. 1 postgres postgres   2640 Oct 10 18:41 pg_ident.conf
-rw-------. 1 postgres postgres   5600 Oct 10 18:41 pg_hba.conf
-rw-------. 1 postgres postgres   1171 Oct 10 18:41 postgresql.conf
drwx------. 2 postgres postgres   4096 Oct 10 18:41 global
-rw-------. 1 postgres postgres     30 Oct 10 18:41 current_logfiles
-rw-------. 1 postgres postgres 227736 Oct 10 18:41 backup_manifest
[postgres@lxicbpgdsgv01 basebackup_10OCT2025]$
B. Copy WAL files from $PGDATA/pg_wal to /pgWal/pgsql17/wal/
[postgres@lxicbpgdsgv01 ~]$ ls -ltr /pgWal/pgsql17/wal/
total 0
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ cd /pgData/pgsql17/data/pg_wal/
[postgres@lxicbpgdsgv01 pg_wal]$ cp -Rp * /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 pg_wal]$
[postgres@lxicbpgdsgv01 pg_wal]$ ls -ltr /pgWal/pgsql17/wal
total 16384
drwx------. 2 postgres postgres        6 Oct 10 18:41 summaries
drwx------. 2 postgres postgres        6 Oct 10 18:41 archive_status
-rw-------. 1 postgres postgres 16777216 Oct 10 18:41 000000010000000000000085
[postgres@lxicbpgdsgv01 pg_wal]$ cd
[postgres@lxicbpgdsgv01 ~]$
C. Remove the existing $PGDATA/pg_wal directory
[postgres@lxicbpgdsgv01 ~]$ rm -rf /pgData/pgsql17/data/pg_wal
[postgres@lxicbpgdsgv01 ~]$
D. Create a symbolic link pointing $PGDATA/pg_wal to a separate WAL directory
[postgres@lxicbpgdsgv01 ~]$ ln -s /pgWal/pgsql17/wal /pgData/pgsql17/data/pg_wal
[postgres@lxicbpgdsgv01 ~]$
[postgres@lxicbpgdsgv01 ~]$ ls -ld /pgData/pgsql17/data/pg_wal
lrwxrwxrwx. 1 postgres postgres 18 Oct 10 19:43 /pgData/pgsql17/data/pg_wal -> /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 ~]$
E. Set Permissions
[postgres@lxicbpgdsgv01 ~]$ chown -R postgres:postgres /pgData/pgsql17/data
[postgres@lxicbpgdsgv01 ~]$ chmod 700 /pgData/pgsql17/data
[postgres@lxicbpgdsgv01 ~]$ chown -R postgres:postgres /pgWal/pgsql17/wal
[postgres@lxicbpgdsgv01 ~]$ chmod 700 /pgWal/pgsql17/wal

6. Start PostgreSQL

[root@lxicbpgdsgv01 ~]# systemctl start postgresql-17.service
[root@lxicbpgdsgv01 ~]# systemctl status postgresql-17.service
● postgresql-17.service - PostgreSQL 17 database server
     Loaded: loaded (/usr/lib/systemd/system/postgresql-17.service; enabled; preset: disabled)
     Active: active (running) since Fri 2025-10-10 19:45:21 +08; 5s ago
       Docs: https://www.postgresql.org/docs/17/static/
    Process: 5230 ExecStartPre=/usr/pgsql-17/bin/postgresql-17-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
   Main PID: 5235 (postgres)
      Tasks: 7 (limit: 15835)
     Memory: 34.2M
        CPU: 94ms
     CGroup: /system.slice/postgresql-17.service
             ├─5235 /usr/pgsql-17/bin/postgres -D /pgData/pgsql17/data/
             ├─5236 "postgres: logger "
             ├─5237 "postgres: checkpointer "
             ├─5238 "postgres: background writer "
             ├─5240 "postgres: walwriter "
             ├─5241 "postgres: autovacuum launcher "
             └─5242 "postgres: logical replication launcher "

Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com systemd[1]: Starting PostgreSQL 17 database server...
Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com postgres[5235]: 2025-10-10 19:45:21.177 +08 [5235] LOG:  redirecting log output to logging collector process
Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com postgres[5235]: 2025-10-10 19:45:21.177 +08 [5235] HINT:  Future log output will appear in directory "log".
Oct 10 19:45:21 lxicbpgdsgv01.rajasekhar.com systemd[1]: Started PostgreSQL 17 database server.
[root@lxicbpgdsgv01 ~]#

7. Final Verification

[postgres@lxicbpgdsgv01 ~]$ psql
psql (17.6)
Type "help" for help.

postgres=# \l+
                                                                                       List of databases
   Name    |  Owner   | Encoding | Locale Provider |   Collate   |    Ctype    | Locale | ICU Rules |   Access privileges   |  Size   | Tablespace |                Description
-----------+----------+----------+-----------------+-------------+-------------+--------+-----------+-----------------------+---------+------------+--------------------------------------------
 dell      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7609 kB | pg_default |
 orcl      | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 7753 kB | pg_default |
 postgres  | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           |                       | 492 MB  | pg_default | default administrative connection database
 template0 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7545 kB | pg_default | unmodifiable empty database
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
 template1 | postgres | UTF8     | libc            | en_SG.UTF-8 | en_SG.UTF-8 |        |           | =c/postgres          +| 7569 kB | pg_default | default template for new databases
           |          |          |                 |             |             |        |           | postgres=CTc/postgres |         |            |
(5 rows)

postgres=# \db
       List of tablespaces
    Name    |  Owner   | Location
------------+----------+----------
 pg_default | postgres |
 pg_global  | postgres |
(2 rows)

postgres=# \c dell
You are now connected to database "dell" as user "postgres".
dell=# select * from test.emp;
 name | designation | project | company
------+-------------+---------+---------
 Sugi | DBA         | Jetstar | iGATE
 Teja | DBA         | RCM     | iGATE
 RAJ  | DBA         | RCM     | iGATE
(3 rows)

dell=#

Caution: Your use of any information or materials on this website is entirely at your own risk. It is provided for educational purposes only. It has been tested internally, however, we do not guarantee that it will work for you. Ensure that you run it in your test environment before using.

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/

PSQL

PostgreSQL, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

PostgreSQL DBA Step by Step Learning

#PostgreSQL DBA Topics
1How to Install PostgreSQL ON Linux?
2How to Install PostgreSQL on Linux 7 using source code?
3How to START/STOP PostgreSQL ON Linux?
4How to Create Database in PostgreSQL?
5PostgreSQL User Management
6PostgreSQL pg_hba.conf Guide
7PostgreSQL Change Data Directory
8Understanding WAL Files in PostgreSQL – For Oracle DBAs
9Change PostgreSQL WAL Directory Path (pg_wal)
10Enable Archive Mode in PostgreSQL 17
11How to Disable ARCHIVELOG Mode
12PostgreSQL Tablespace Management
13PostgreSQL pg_dump and pg_restore Guide
14PostgreSQL Backup and Restore Using pg_dumpall and psql
15pg_basebackup – Backup, Restore, and Recovery
16Backup & Restore PostgreSQL DB Cluster to Another Host (No Archive Mode)
17Backup & Restore PostgreSQL DB Cluster on Same Host
18Restore PostgreSQL to New Host using pg_basebackup + WAL Archives
19PostgreSQL PITR – Point in Time Recovery
20Configure Streaming Replication in PostgreSQL
21Manual Failover in PostgreSQL Streaming Replication
22Convert Asynchronous Replication to Synchronous Replication

 

Thank you,
Rajasekhar Amudala
Email: br8dba@gmail.com
Linkedin: https://www.linkedin.com/in/rajasekhar-amudala/