The QuasarDB daemon reports "out of free sessions"

Summary

The QuasarDB daemon reports the following error:

warning  out of free sessions, trying again in 600 seconds

Clients might experience reliability issues, and sessions time out.

Cause

All operating systems put limits on the maximum number of file descriptors or TCP connections a process can use. In QuasarDB, each client uses a dedicated connection to each partition it wants to write to. When this error occurs, it means QuasarDB is unable to reserve a new connections for clients.

Resolution

Option 1: Ensure sessions are properly cleaned up

The most effective solution to this is to ensure you are using proper resource management client-side. Ensure that you are tearing down your QuasarDB sessions after you are not using them anymore, so that connections free up for QuasarDB daemon to repurpose for another client. 

Once you have established that you are not holding onto resources longer than strictly required, continue with option 2.

Option 2: Increase your limits server-side

QuasarDB reserves a fixed amount of connections for each partition, configurable with the --sessions command line option, and you will likely want to tune this variable in production deployments. 

Warning: increasing the number of sessions means that QuasarDB might hit the upper limit of the number of file descriptors the operating system allows the process to use. Make sure to tune the limits put in place by your operating system as well.

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