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PostgreSQL

24/11/18 - using Postgres a bit more as it relates to pgvector and supabase.

Log

  • 24/11/18 - upgraded to version 17 since brew pgvector only supports @14 & @17 and ran into a couple issues 👇🏼

  • change path in .zshrc

export PATH="/opt/homebrew/opt/postgresql@17/bin:$PATH"
david@ovid🏛 :~ » brew uninstall postgresql@15
Uninstalling /opt/homebrew/Cellar/postgresql@15/15.8_3... (3,706 files, 62.6MB)
david@ovid🏛 :~ » brew uninstall pgvector
Uninstalling /opt/homebrew/Cellar/pgvector/0.8.0... (86 files, 511.7KB)
david@ovid🏛 :~ » brew install postgresql@17
david@ovid🏛 :~ » psql postgres 2
psql (17.0 (Homebrew))
Type "help" for help.

postgres=# \dx
List of installed extensions
Name | Version | Schema | Description
---------+---------+------------+------------------------------
plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language
(1 row)

postgres=# CREATE EXTENSION pgvector;
ERROR: extension "pgvector" is not available
DETAIL: Could not open extension control file "/opt/homebrew/share/postgresql@17/extension/pgvector.control": No such file or directory.
HINT: The extension must first be installed on the system where PostgreSQL is running.
postgres=# \du
List of roles
Role name | Attributes
-----------+------------------------------------------------------------
david | Superuser, Create role, Create DB, Replication, Bypass RLS

postgres=# \q

david@ovid🏛 :~ » which pg_config
/opt/homebrew/opt/postgresql@17/bin/pg_config
david@ovid🏛 :~ » brew info pgvector
==> pgvector: stable 0.8.0 (bottled)
Open-source vector similarity search for Postgres
https://github.com/pgvector/pgvector
Installed
/opt/homebrew/Cellar/pgvector/0.8.0 (86 files, 511.7KB) *
Poured from bottle using the formulae.brew.sh API on 2024-11-18 at 16:14:38
From: https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/p/pgvector.rb
License: PostgreSQL
==> Dependencies
Build: postgresql@14 ✘, postgresql@17 ✔
==> Analytics
install: 870 (30 days), 2,270 (90 days), 8,271 (365 days)
install-on-request: 871 (30 days), 2,269 (90 days), 8,271 (365 days)
build-error: 9 (30 days)

david@ovid🏛 :~ » psql postgres
psql (17.0 (Homebrew))
postgres=# CREATE EXTENSION vector;
CREATE EXTENSION
postgres-# \dx
List of installed extensions
Name | Version | Schema | Description
---------+---------+------------+------------------------------------------------------
plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language
vector | 0.8.0 | public | vector data type and ivfflat and hnsw access methods


Cheat Sheet

Magic words:

psql -U postgres

Some interesting flags (to see all, use -h or --help depending on your psql version):

  • -E: will describe the underlaying queries of the \ commands (cool for learning!)
  • -l: psql will list all databases and then exit (useful if the user you connect with doesn't has a default database, like at AWS RDS)

Most \d commands support additional param of __schema__.name__ and accept wildcards like *.*

  • \?: Show help (list of available commands with an explanation)
  • \q: Quit/Exit
  • \c __database__: Connect to a database
  • \d __table__: Show table definition (columns, etc.) including triggers
  • \d+ __table__: More detailed table definition including description and physical disk size
  • \l: List databases
  • \dy: List events
  • \df: List functions
  • \di: List indexes
  • \dn: List schemas
  • \dt *.*: List tables from all schemas (if *.* is omitted will only show SEARCH_PATH ones)
  • \dT+: List all data types
  • \dv: List views
  • \dx: List all extensions installed
  • \df+ __function__ : Show function SQL code.
  • \x: Pretty-format query results instead of the not-so-useful ASCII tables
  • \copy (SELECT * FROM __table_name__) TO 'file_path_and_name.csv' WITH CSV: Export a table as CSV
  • \des+: List all foreign servers
  • \dE[S+]: List all foreign tables
  • \! __bash_command__: execute __bash_command__ (e.g. \! ls)

User Related:

  • \du: List users
  • \du __username__: List a username if present.
  • create role __test1__: Create a role with an existing username.
  • create role __test2__ noinherit login password __passsword__;: Create a role with username and password.
  • set role __test__;: Change role for current session to __test__.
  • grant __test2__ to __test1__;: Allow __test1__ to set its role as __test2__.
  • \deu+: List all user mapping on server

Configuration

  • Service management commands:
sudo service postgresql stop
sudo service postgresql start
sudo service postgresql restart
  • Changing verbosity & querying Postgres log:
    1) First edit the config file, set a decent verbosity, save and restart postgres:
sudo vim /etc/postgresql/9.3/main/postgresql.conf

# Uncomment/Change inside:
log_min_messages = debug5
log_min_error_statement = debug5
log_min_duration_statement = -1

sudo service postgresql restart
  1. Now you will get tons of details of every statement, error, and even background tasks like VACUUMs
tail -f /var/log/postgresql/postgresql-9.3-main.log
  1. How to add user who executed a PG statement to log (editing postgresql.conf):
log_line_prefix = '%t %u %d %a '
  • Check Extensions enabled in postgres: SELECT * FROM pg_extension;

  • Show available extensions: SELECT * FROM pg_available_extension_versions;

Create command

There are many CREATE choices, like CREATE DATABASE __database_name__, CREATE TABLE __table_name__ ... Parameters differ but can be checked at the official documentation.

Handy queries

  • SELECT * FROM pg_proc WHERE proname='__procedurename__': List procedure/function
  • SELECT * FROM pg_views WHERE viewname='__viewname__';: List view (including the definition)
  • SELECT pg_size_pretty(pg_total_relation_size('__table_name__'));: Show DB table space in use
  • SELECT pg_size_pretty(pg_database_size('__database_name__'));: Show DB space in use
  • show statement_timeout;: Show current user's statement timeout
  • SELECT * FROM pg_indexes WHERE tablename='__table_name__' AND schemaname='__schema_name__';: Show table indexes
  • Get all indexes from all tables of a schema:
SELECT
t.relname AS table_name,
i.relname AS index_name,
a.attname AS column_name
FROM
pg_class t,
pg_class i,
pg_index ix,
pg_attribute a,
pg_namespace n
WHERE
t.oid = ix.indrelid
AND i.oid = ix.indexrelid
AND a.attrelid = t.oid
AND a.attnum = ANY(ix.indkey)
AND t.relnamespace = n.oid
AND n.nspname = 'kartones'
ORDER BY
t.relname,
i.relname
  • Execution data:
    • Queries being executed at a certain DB:
SELECT datname, application_name, pid, backend_start, query_start, state_change, state, query 
FROM pg_stat_activity
WHERE datname='__database_name__';
  • Get all queries from all dbs waiting for data (might be hung):
SELECT * FROM pg_stat_activity WHERE waiting='t'
  • Currently running queries with process pid:
SELECT 
pg_stat_get_backend_pid(s.backendid) AS procpid,
pg_stat_get_backend_activity(s.backendid) AS current_query
FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;
  • Get Connections by Database: SELECT datname, numbackends FROM pg_stat_database;

Casting:

  • CAST (column AS type) or column::type
  • '__table_name__'::regclass::oid: Get oid having a table name

Query analysis:

  • EXPLAIN __query__: see the query plan for the given query
  • EXPLAIN ANALYZE __query__: see and execute the query plan for the given query
  • ANALYZE [__table__]: collect statistics

Generating random data (source):

  • INSERT INTO some_table (a_float_value) SELECT random() * 100000 FROM generate_series(1, 1000000) i;

Get sizes of tables, indexes and full DBs:

select current_database() as database,
pg_size_pretty(total_database_size) as total_database_size,
schema_name,
table_name,
pg_size_pretty(total_table_size) as total_table_size,
pg_size_pretty(table_size) as table_size,
pg_size_pretty(index_size) as index_size
from ( select table_name,
table_schema as schema_name,
pg_database_size(current_database()) as total_database_size,
pg_total_relation_size(table_name) as total_table_size,
pg_relation_size(table_name) as table_size,
pg_indexes_size(table_name) as index_size
from information_schema.tables
where table_schema=current_schema() and table_name like 'table_%'
order by total_table_size
) as sizes;
COPY table_name [ ( column_name [, ...] ) ]
FROM { 'filename' | STDIN }
[ [ WITH ] ( option [, ...] ) ]

COPY { table_name [ ( column_name [, ...] ) ] | ( query ) }
TO { 'filename' | STDOUT }
[ [ WITH ] ( option [, ...] ) ]
  • List all grants for a specific user
SELECT table_catalog, table_schema, table_name, privilege_type
FROM information_schema.table_privileges
WHERE grantee = 'user_to_check' ORDER BY table_name;
  • List all assigned user roles
SELECT
r.rolname,
r.rolsuper,
r.rolinherit,
r.rolcreaterole,
r.rolcreatedb,
r.rolcanlogin,
r.rolconnlimit,
r.rolvaliduntil,
ARRAY(SELECT b.rolname
FROM pg_catalog.pg_auth_members m
JOIN pg_catalog.pg_roles b ON (m.roleid = b.oid)
WHERE m.member = r.oid) as memberof,
r.rolreplication
FROM pg_catalog.pg_roles r
ORDER BY 1;
  • Check permissions in a table:
SELECT grantee, privilege_type
FROM information_schema.role_table_grants
WHERE table_name='name-of-the-table';
  • Kill all Connections:
SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE datname = current_database() AND pid <> pg_backend_pid();

Keyboard shortcuts

  • CTRL + R: reverse-i-search

Tools

$ echo "bind "^R" em-inc-search-prev" > $HOME/.editrc
$ source $HOME/.editrc
  • Show IP of the DB Instance: SELECT inet_server_addr();
  • File to save PostgreSQL credentials and permissions (format: hostname:port:database:username:password): chmod 600 ~/.pgpass
  • Collect statistics of a database (useful to improve speed after a Database Upgrade as previous query plans are deleted): ANALYZE VERBOSE;
  • To obtain the CREATE TABLE query of a table, any visual GUI like pgAdmin allows to easily, but else you can use pg_dump, e.g.: pg_dump -t '<schema>.<table>' --schema-only <database> (source)

Resources & Documentation

  • Operations Cheat Sheet: Official PG wiki cheat sheet with an amazing amount of explanations of many topics, features, and many many internal implementation details
  • Postgres Weekly newsletter: The best way IMHO to keep up to date with PG news
  • 100 psql Tips: Name says all, lots of useful tips!
  • PostgreSQL Exercises: An awesome resource to learn to learn SQL, teaching you with simple examples in a great visual way. Highly recommended.
  • A Performance Cheat Sheet for PostgreSQL: Great explanations of EXPLAIN, EXPLAIN ANALYZE, VACUUM, configuration parameters and more. Quite interesting if you need to tune-up a postgres setup.
  • annotated.conf: Annotations of all 269 postgresql.conf settings for PostgreSQL 10.
  • psql -c "\l+" -H -q postgres > out.html: Generate a html report of your databases (source: