Spool out all parameters from a datafile to a file

psql -h postgres01.oric.no -U mysuperuser postgres -c "COPY (SELECT name || '='  || setting FROM pg_settings ORDER BY name) TO STDOUT WITH CSV HEADER"   > pg_config.csv

List a table, its partitions and the number of rows it contains

SELECT
    s.schemaname,
    s.relname AS table_name,
    s.n_live_tup,
    s.last_analyze,
    s.last_autoanalyze
FROM
    pg_stat_all_tables s
JOIN
    pg_class c ON c.relname = s.relname
LEFT JOIN
    pg_inherits i ON i.inhrelid = c.oid OR i.inhparent = c.oid
WHERE
    s.schemaname = 'myschema'
    AND (
        s.relname = 'mytable'
        OR c.oid IN (
            SELECT inhrelid
            FROM pg_inherits
            WHERE inhparent = (
                SELECT oid FROM pg_class WHERE relname = 'mytable'
            )
        )
    )
ORDER BY
 s.n_live_tup DESC,s.last_analyze;

Example output

 schemaname      |  table_name     | n_live_tup | last_analyze   		| last_autoanalyze 
-----------------+-----------------+------------+-------------------------------+------------------------------
 myschema 	 | mytable_2015_02 |   95788115 | 2025-08-06 12:58:22.952592+00 | 
 myschema 	 | mytable_2015_03 |   78505350 | 2025-08-06 12:58:37.147433+00 | 
 myschema 	 | mytable_2015_04 |   71211253 | 2025-08-06 12:58:51.311452+00 | 
 myschema 	 | mytable_2015_01 |   68255510 | 2025-08-06 12:58:08.42708+00  | 
 myschema 	 | mytable_2015_05 |   62075043 | 2025-08-06 12:59:05.434118+00 | 
 myschema 	 | mytable_2015_06 |   60888876 | 2025-08-06 12:59:19.918657+00 | 2025-08-06 11:31:19.551345+00
 myschema 	 | mytable_2015_12 |   57485594 | 2025-08-06 13:00:43.112316+00 | 2025-08-27 03:13:11.394606+00
 myschema 	 | mytable_2016_01 |   57405307 | 2025-08-06 13:00:55.395113+00 | 2025-08-25 13:35:07.749773+00

How to check if a PostgreSQL streaming replicate server is up-to-date with the primary

On the primary, run

SELECT pg_current_wal_lsn(); -- On the primary

In my case, the result was

 pg_current_wal_lsn
--------------------
 0/E015420

On the standby, run

SELECT pg_last_wal_replay_lsn();

In my case, the result was

pg_last_wal_replay_lsn
------------------------
 0/E015420

This means that

All WAL records have been received

All WAL recores have been replayed (not just flushed) on the standby

There is no lag between primary and standby

Basic postgres connect syntax

psql -h hostname -U username -d database

Options:

Option	Description
-h <host>	Hostname or IP address of the PostgreSQL server
-p <port>	Port number (default is 5432)
-U <username>	Username to connect as
-d <dbname>	Database name
-W Prompt for password (useful if password auth is required)
-f <filename>	Execute commands from a SQL script file
-c "<command>"	Execute a single SQL command and exit
-v var=value	Set psql variable (used inside scripts)
--set=var=value	Same as -v, more explicit
--dbname=<connstr>	Full connection string, e.g.: postgresql://user:pass@host:port/dbname

Example

psql -h pg01.oric.no -p 5432 -U myuser -d mydb

Alternatively, use an URL, which is more scripting friendly:

psql "postgresql://replicate@pg01.oric.no:5432/mydb"

How to find the columns in a specific postgres data dictionary table

For example, to check which columns belongs to the view "pg_stat_wal_receiver"

SELECT column_name
FROM information_schema.columns
WHERE table_name = 'pg_stat_wal_receiver';

Output

     column_name
-----------------------
 pid
 last_msg_receipt_time
 latest_end_lsn
 latest_end_time
 sender_port
 receive_start_lsn
 receive_start_tli
 written_lsn
 flushed_lsn
 received_tli
 last_msg_send_time
 status
 slot_name
 sender_host
 conninfo
(15 rows)

Or use the psql metacommand "\d+":

echo '\d+ pg_stat_wal_receiver' |psql

Output

                                  View "pg_catalog.pg_stat_wal_receiver"
        Column         |           Type           | Collation | Nullable | Default | Storage  | Description
-----------------------+--------------------------+-----------+----------+---------+----------+-------------
 pid                   | integer                  |           |          |         | plain    |
 status                | text                     |           |          |         | extended |
 receive_start_lsn     | pg_lsn                   |           |          |         | plain    |
 receive_start_tli     | integer                  |           |          |         | plain    |
 written_lsn           | pg_lsn                   |           |          |         | plain    |
 flushed_lsn           | pg_lsn                   |           |          |         | plain    |
 received_tli          | integer                  |           |          |         | plain    |
 last_msg_send_time    | timestamp with time zone |           |          |         | plain    |
 last_msg_receipt_time | timestamp with time zone |           |          |         | plain    |
 latest_end_lsn        | pg_lsn                   |           |          |         | plain    |
 latest_end_time       | timestamp with time zone |           |          |         | plain    |
 slot_name             | text                     |           |          |         | extended |
 sender_host           | text                     |           |          |         | extended |
 sender_port           | integer                  |           |          |         | plain    |
 conninfo              | text                     |           |          |         | extended |
View definition:
 SELECT pid,
    status,
    receive_start_lsn,
    receive_start_tli,
    written_lsn,
    flushed_lsn,
    received_tli,
    last_msg_send_time,
    last_msg_receipt_time,
    latest_end_lsn,
    latest_end_time,
    slot_name,
    sender_host,
    sender_port,
    conninfo
   FROM pg_stat_get_wal_receiver() s(pid, status, receive_start_lsn, receive_start_tli, written_lsn, flushed_lsn, received_tli, last_msg_send_time, last_msg_receipt_time, latest_end_lsn, latest_end_time, slot_name, sender_host, sender_port, conninfo)
  WHERE pid IS NOT NULL;

How to list the postgres processes running on your server and what their jobs are

A neet little trick I learned from the series "Mirage of memory, part 2: PSS"

ps -fu postgres | grep $(pgrep -f postmaster)
postgres    1913       1  0 Jul17 ?        00:02:51 /usr/pgsql-15/bin/postmaster -D /var/lib/pgsql/15/data/
postgres    1982    1913  0 Jul17 ?        00:00:24 postgres: logger
postgres    2063    1913  0 Jul17 ?        00:00:18 postgres: checkpointer
postgres    2064    1913  0 Jul17 ?        00:00:03 postgres: background writer
postgres    2119    1913  0 Jul17 ?        00:00:07 postgres: walwriter
postgres    2120    1913  0 Jul17 ?        00:00:14 postgres: autovacuum launcher
postgres    2121    1913  0 Jul17 ?        00:00:01 postgres: archiver
postgres    2122    1913  0 Jul17 ?        00:00:00 postgres: logical replication launcher
postgres    2657    1913  0 Jul17 ?        00:02:05 postgres: postgres_exporter postgres localhost(48674) idle

The command lists all processes by user "postgres" and and greps for the output of the command "pgrep -f postmaster", which returns a list of process IDs

You could also count the number of processes by user "postgres" by simply typing

pgrep -c postmaster
9

How to find when a PostgreSQL table was last vacuumed

SELECT
schemaname,
relname,
last_vacuum,
last_autovacuum,
last_analyze,
last_autoanalyze
FROM pg_stat_user_tables
WHERE relname = 'documents';
   schemaname   | relname  | last_vacuum |        last_autovacuum        |         last_analyze          |       last_autoanalyze
----------------+----------+-------------+-------------------------------+-------------------------------+-------------------------------
 scott          | documents|             | 2025-06-25 02:05:20.692869+02 | 2025-07-12 22:04:05.119051+02 | 2025-06-17 08:41:12.567351+02
(1 row)

Explanation of columns:

last_vacuum: Last manual vacuum.

last_autovacuum: Last automatic vacuum.

last_analyze: Last manual analyze.

last_autoanalyze: Last automatic analyze.

What does ANALYZE do in PostgreSQL?

ANALYZE collects statistics about the contents of a table (or all tables), such as:

Number of rows

Distribution of values

Most common values

Histogram of value ranges

Null fractions These statistics are stored in pg_statistic and are used by the query planner to make decisions (e.g., which index to use, join strategies, etc.).

Syntax to run ANALYZE

Analyze the entire database (all tables in all schemas):

ANALYZE;

Analyze a specific table:

ANALYZE my_table;

Analyze specific columns only:

ANALYZE my_table (column1, column2);