add notes: psql common issues

content/notes/psql-common-issues.md

@@ -0,0 +1,68 @@
+---
+title: "Psql Common Issues"
+date: 2024-05-29T01:16:51+05:30
+tags: ["postgres", "unix"]
+description: "Today I learned some psql common issues"
+---
+
+Whenever I install there are a few issues that are common but I wasn't aware why they occured. Today I also had some issues which now I understand, so I am writing these notes for future reference. Hopefully I don't require these in future.
+
+# psql
+Beginning with the command psql, let's understand what it is and what it does.
+It is one of the utitlity that is installed when you install postgres along with other programs such createdb, dropdb, createuser, and more.
+
+```
+$ psql
+psql: error: FATAL:  database "karan.y" does not exist
+```
+
+When you run this command you get dropped into a psql shell which connects to a database having the same name as current user by default. You can specifiy the database as follows -
+
+`psql <database>`
+
+You can list all the databases as follows - 
+```
+$ psql -l                          
+                                  List of databases
+       Name        |  Owner   | Encoding | Collate | Ctype |    Access privileges    
+-------------------+----------+----------+---------+-------+-------------------------
+ postgres          | karan.y  | UTF8     | C       | C     | 
+ template0         | karan.y  | UTF8     | C       | C     | =c/"karan.y"           +
+                   |          |          |         |       | "karan.y"=CTc/"karan.y"
+ template1         | karan.y  | UTF8     | C       | C     | =c/"karan.y"           +
+                   |          |          |         |       | "karan.y"=CTc/"karan.y"
+(5 rows)
+```
+
+You can drop into the postgres database with the current user and create a new role `postgres`. It can also be created the createuser postgres utitlity. Then you can drop into psql shell with postgres role
+```
+$ createuser postgres
+$ psql -U postgres my_database
+```
+
+
+
+# server error
+Another error that you might receive is this - 
+
+```
+$ psql                              
+psql: error: could not connect to server: No such file or directory
+        Is the server running locally and accepting
+        connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
+```
+
+Let's understand what this error means -
+
+```
+In Unix and Unix-like operating systems, a Unix domain socket (also known as an IPC socket) is a type of socket that is used for inter-process communication (IPC). A Unix domain socket is similar to a network socket, but it is used to communicate between processes on the same system, rather than between processes on different systems.
+
+The PostgreSQL database server uses the Unix domain socket to listen for incoming connections from PostgreSQL client applications. A PostgreSQL client application is a process that runs on a Unix or Unix-like operating system and is responsible for interacting with the PostgreSQL database.
+
+When a PostgreSQL client application wants to connect to the PostgreSQL database server, it can use the Unix domain socket to establish a connection. The PostgreSQL database server will then accept the connection and allow the PostgreSQL client application to interact with the PostgreSQL database.
+```
+
+This will probably be fixed by starting the postgres service -
+
+`brew services start postgresql@14`
+