May 17, 2026, 11:40 PM

2026-05-18 06:40:19 +00:00
commit 64944cf004
896 changed files with 310709 additions and 0 deletions
@@ -0,0 +1,37 @@
+How to connect to postgres db:
+
+set PATH if not done:
+
+postgres$ export PATH=/Library/PostgreSQL/10/bin:$PATH
+postgres$ which psql
+/Library/PostgreSQL/10/bin/psql
+
+connect to db using SYNTAX - psql -d -U
+
+postgres$ psql -d edb -U postgres
+Password for user postgres:
+psql (10.13)
+Type "help" for help.
+
+postgres=#
+
+Find current connection info:
+
+postgres=# \conninfo
+You are connected to database "edb" as user "postgres" via socket in "/tmp" at port "5432".
+
+ 
+
+postgres=# select current_schema,current_user,session_user,current_database();
+current_schema  | current_user | session_user | current_database
+----------------+--------------+--------------+------------------
+public         | postgres.     | postgres     | edb
+
+ 
+
+Switch to another database:
+
+postgres-# \c dbaclass
+You are now connected to database "dbaclass" as user "postgres".
+
+ 
@@ -0,0 +1,18 @@
+DATA_DIRECTORY - > Specifies the directory to use for data storage.
+
+dbaclass=# show data_directory;
+
+data_directory
+-----------------------------
+/Library/PostgreSQL/10/data
+(1 row)
+
+dbaclass=# select setting from pg_settings where name = 'data_directory';
+setting
+-----------------------------
+/Library/PostgreSQL/10/data
+(1 row)
+
+-- This will show location of important files in postgres
+
+dbaclass=# SELECT name, setting FROM pg_settings WHERE category = 'File Locations';
@@ -0,0 +1,21 @@
+- Drop database from psql
+Note - while dropping a database, you need to connect to a database other than the db you are trying to drop.
+
+postgres=# \conninfo
+You are connected to database "postgres" as user "postgres" on host "localhost" at port "5432".
+
+postgres#drop database "DBACLASS";
+
+-- Drop database using dropdb os utility
+
+postgres$ pwd
+/Library/PostgreSQL/10/bin
+
+postgres$ ./dropdb -e "DBACLASS"
+Password:
+SELECT pg_catalog.set_config('search_path', '', false)
+DROP DATABASE "DBACLASS";
+
+ 
+
+For complete article visit -  > https://dbaclass.com/article/drop-database-postgres/
@@ -0,0 +1,19 @@
+1. Create directory for archiving:
+
+mkdir -p /Library/PostgreSQL/10/data/archive/
+
+2. Update the postgres.conf file with below values
+
+wal_level = replica
+archive_mode = on
+max_wal_senders=1
+archive_command= 'test ! -f /Library/PostgreSQL/10/data/archive/%f && cp %p /Library/PostgreSQL/10/data/archive/%f'
+
+3. Restart the postgres servers
+
+export PGDATA=/Library/PostgreSQL/10/data
+pg_ctl stop
+pg_ctl start
+
+3. Check archive status:
+postgres=# select name,setting from pg_settings where name like 'archive%';
@@ -0,0 +1,15 @@
+-- Find list of installed extension:
+
+psql# \dx
+
+(or)
+
+psql#\dx+
+
+(or)
+
+psql#SELECT * FROM pg_extension;
+
+-- For finding available extension in server:
+
+psql# SELECT * FROM pg_available_extensions;
@@ -0,0 +1,3 @@
+-- QUERY TO FIND BLOCKING SESSION DETAILS
+
+dbaclass#select pid as blocked_pid, usename, pg_blocking_pids(pid) as "blocked_by(pid)", query as blocked_query from pg_stat_activity where cardinality(pg_blocking_pids(pid)) > 0;
@@ -0,0 +1,32 @@
+Find location of postgres related conf files
+
+dbaclass=# SELECT name, setting FROM pg_settings WHERE category = 'File Locations';
+name                     | setting
+-------------------+---------------------------------------------
+config_file              | /Library/PostgreSQL/10/data/postgresql.conf
+data_directory           | /Library/PostgreSQL/10/data
+external_pid_file        |
+hba_file                 | /Library/PostgreSQL/10/data/pg_hba.conf
+ident_file               | /Library/PostgreSQL/10/data/pg_ident.conf
+(5 rows)
+
+alternatively:
+
+postgres=# show config_file;
+
+                 config_file
+--------------------------------------------
+
+/Library/PostgreSQL/10/data/postgresql.conf
+
+(1 row)
+
+postgres=# show hba_file;
+
+                hba_file
+-----------------------------------------
+/Library/PostgreSQL/10/data/pg_hba.conf
+
+(1 row)
+
+postgres=# show ident_file;
@@ -0,0 +1 @@
+select t.relname,l.locktype,page,virtualtransaction,pid,mode,granted from pg_locks l, pg_stat_all_tables t where l.relation=t.relid order by relation asc;
@@ -0,0 +1,25 @@
+Find sessions in the postgres:
+
+select pid as process_id,
+usename as username,
+datname as database_name,
+client_addr as client_address,
+application_name,
+backend_start,
+state,
+state_change,query
+from pg_stat_activity;
+
+ 
+
+-- For specific database:
+
+select pid as process_id,
+usename as username,
+datname as database_name,
+client_addr as client_address,
+application_name,
+backend_start,
+state,
+state_change,query 
+from pg_stat_activity where datname='dbaclass';
@@ -0,0 +1,5 @@
+postgres=# SELECT pg_database.datname as "database_name", pg_size_pretty(pg_database_size(pg_database.datname)) AS size_in_mb FROM pg_database ORDER by size_in_mb DESC;
+
+(or)
+
+postgres=# \l+
@@ -0,0 +1,7 @@
+-- First find the pid of the session:
+
+dbaclass#SELECT datname as database, pid as pid, usename as username, application_name , client_addr , query FROM pg_stat_activity;
+
+<< Lets say the pid=1124, in the below query pass the pid value to kill that particular session..>>
+
+dbaclass#select pg_terminate_backend(pid) from pg_stat_activity where pid='1123';
@@ -0,0 +1,8 @@
+-- Here we want to kill all session of the user postgres
+
+-- List all the session of that user.
+dbaclass#select datname as database, pid as pid, usename as username, application_name , client_addr, query FROM pg_stat_activity where username='postgres';
+
+-- Kill all the session of user postgres.
+
+dbaclass#select pg_terminate_backend(pid) from pg_stat_activity where usename='postgres';
@@ -0,0 +1,17 @@
+-- Last pg config reload time
+
+postgres=# select pg_conf_load_time() ;
+pg_conf_load_time
+----------------------------------
+2020-07-06 13:20:18.048689+05:30
+(1 row)
+
+-- Reload again and see whether reload time changed or not
+
+postgres=# select pg_reload_conf();
+pg_reload_conf
+----------------
+t
+(1 row)
+
+postgres=# select pg_conf_load_time() ;
@@ -0,0 +1,13 @@
+postgres=# \list+
+List of databases
+Name | Owner | Encoding | Collate | Ctype | Access privileges | Size | Tablespace | Description
+-----------+----------+----------+---------+-------+-----------------------+---------+------------+--------------------------------------------
+dbaclass | postgres | UTF8 | C | C | | 2268 MB | pg_default |
+postgres | postgres | UTF8 | C | C | | 4132 MB | pg_default | default administrative connection database
+template0 | postgres | UTF8 | C | C | =c/postgres +| 7601 kB | pg_default | unmodifiable empty database
+| | | | | postgres=CTc/postgres | | |
+template1 | postgres | UTF8 | C | C | =c/postgres +| 7601 kB | pg_default | default template for new databases
+| | | | | postgres=CTc/postgres | | |
+(4 rows)
+
+postgres=# select datname from pg_database;
@@ -0,0 +1,3 @@
+-- Below command signals the log-file manager to switch to a new output file immediately.it is just like an alert log
+
+select pg_rotate_logfile() ;
@@ -0,0 +1,21 @@
+dbaclass=# show server_version;
+server_version
+----------------
+10.13
+(1 row)
+
+dbaclass=# select version ();
+version
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------
+PostgreSQL 10.13 on x86_64-apple-darwin, compiled by i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00), 64-bit
+(1 row)
+
+postgres$ cd /Library/PostgreSQL/10/bin
+
+postgres$ ./postgres -V
+postgres (PostgreSQL) 10.13
+
+-- PG_VERSION file is under data directory
+postgres$ cd /Library/PostgreSQL/10/data
+
+postgres$ cat PG_VERSION
@@ -0,0 +1,19 @@
+-- Monitor query execution time
+
+select substr(query,1,100) query,calls,min_time/1000 "min_time(in sec)" , max_time/1000 "max_time(in sec)", mean_time/1000 "avg_time(in sec)", rows from pg_stat_statements order by mean_time desc;
+
+-------------------------------------------------------------------------------------------------------------------------------------------------------
+
+NOTE:
+
+If pg_stat_statements is not available in your database, then activate using below:
+-- Add below parameters in postgres.conf file and restart the postgres cluster
+
+shared_preload_libraries = 'pg_stat_statements'
+pg_stat_statements.track = all
+
+sudo service postgresql restart
+
+-- Now create extension:
+
+dbaclass=# create extension pg_stat_statements;
@@ -0,0 +1,11 @@
+-- Uptime of server
+
+postgres# SELECT now() - pg_postmaster_start_time() "uptime";
+uptime
+------------------------
+9 days 04:54:56.774981
+(1 row)
+
+-- Server startup time:
+
+postgres# SELECT pg_postmaster_start_time();
@@ -0,0 +1 @@
+select pg_switch_wal();
@@ -0,0 +1,34 @@
+-- Below commands can be used to find postgres db date/timestamp
+
+postgres=# SELECT CURRENT_TIMESTAMP;
+current_timestamp
+----------------------------------
+2020-07-06 17:45:24.929293+05:30
+(1 row)
+
+postgres=# select current_date;
+current_date
+--------------
+2020-07-06
+(1 row)
+
+postgres=# select statement_timestamp() ;
+statement_timestamp
+----------------------------------
+2020-07-06 17:46:16.825492+05:30
+(1 row)
+
+postgres=# select timeofday() ;
+timeofday
+-------------------------------------
+Mon Jul 06 17:46:23.861551 2020 IST
+(1 row)
+
+postgres=# select localtime(0);
+localtime
+-----------
+17:52:38
+(1 row)
+
+postgres=# select localtimestamp(0);
+localtimestamp
@@ -0,0 +1,12 @@
+dbaclass=# show timezone
+TimeZone
+--------------
+Asia/Kolkata
+(1 row)
+
+dbaclass=# SELECT current_setting('TIMEZONE');
+current_setting
+-----------------
+Asia/Kolkata
+
+dbaclass=# select name,setting,short_desc,boot_val from pg_settings where name='TimeZone';
				`@@ -0,0 +1 @@`
				`select t.relname,l.locktype,page,virtualtransaction,pid,mode,granted from pg_locks l, pg_stat_all_tables t where l.relation=t.relid order by relation asc;`