How to increase the max connections in postgres? - postgresql

Question

I am using Postgres DB for my product. While doing the batch insert using slick 3, I am getting an error message:
org.postgresql.util.PSQLException: FATAL: sorry, too many clients already.
My batch insert operation will be more than thousands of records.
Max connection for my postgres is 100.
How to increase the max connections?

Answer 1

Just increasing max_connections is bad idea. You need to increase shared_buffers and kernel.shmmax as well.
Considerations
max_connections determines the maximum number of concurrent connections to the database server. The default is typically 100 connections.
Before increasing your connection count you might need to scale up your deployment. But before that, you should consider whether you really need an increased connection limit.
Each PostgreSQL connection consumes RAM for managing the connection or the client using it. The more connections you have, the more RAM you will be using that could instead be used to run the database.
A well-written app typically doesn't need a large number of connections. If you have an app that does need a large number of connections then consider using a tool such as pg_bouncer which can pool connections for you. As each connection consumes RAM, you should be looking to minimize their use.
How to increase max connections
1. Increase max_connection and shared_buffers
in /var/lib/pgsql/{version_number}/data/postgresql.conf
change
max_connections = 100
shared_buffers = 24MB
to
max_connections = 300
shared_buffers = 80MB
The shared_buffers configuration parameter determines how much memory is dedicated to PostgreSQL to use for caching data.
If you have a system with 1GB or more of RAM, a reasonable starting
value for shared_buffers is 1/4 of the memory in your system.
it's unlikely you'll find using more than 40% of RAM to work better
than a smaller amount (like 25%)
Be aware that if your system or PostgreSQL build is 32-bit, it might
not be practical to set shared_buffers above 2 ~ 2.5GB.
Note that on Windows, large values for shared_buffers aren't as
effective, and you may find better results keeping it relatively low
and using the OS cache more instead. On Windows the useful range is
64MB to 512MB.
2. Change kernel.shmmax
You would need to increase kernel max segment size to be slightly larger
than the shared_buffers.
In file /etc/sysctl.conf set the parameter as shown below. It will take effect when postgresql reboots (The following line makes the kernel max to 96Mb)
kernel.shmmax=100663296
References
Postgres Max Connections And Shared Buffers
Tuning Your PostgreSQL Server

Answer 2

Adding to Winnie's great answer,
If anyone is not able to find the postgresql.conf file location in your setup, you can always ask the postgres itself.
SHOW config_file;
For me changing the max_connections alone made the trick.
EDIT: From #gies0r: In Ubuntu 18.04 it is at
/etc/postgresql/11/main/postgresql.conf

Answer 3

If your postgres instance is hosted by Amazon RDS, Amazon configures the max connections for you based on the amount of memory available.
Their documentation says you get 112 connections per 1 GB of memory (with a limit of 5000 connections no matter how much memory you have), but we found we started getting error messages closer to 80 connections in an instance with only 1 GB of memory. Increasing to 2 GB let us use 110 connections without a problem (and probably more, but that's the most we've tried so far.) We were able to increase the memory of an existing instance from 1 GB to 2 GB in just a few minutes pretty easily.
Here's the link to the relevant Amazon documentation:
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Limits.html#RDS_Limits.MaxConnections

Answer 4

change max_connections variable
in postgresql.conf file located in
/var/lib/pgsql/data or /usr/local/pgsql/data/

Answer 5

Locate postgresql.conf file by below command
locate postgresql.conf
Edit postgresql.conf file by below command
sudo nano /etc/postgresql/14/main/postgresql.conf
Change
max_connections = 100
shared_buffers = 24MB
to
max_connections = 300
shared_buffers = 80MB