Why do write commands to RT Sphinx index go into infinite timeout?

Question

Sphinx

When executing write commands (INSERT, REPLACE, DELETE) on RT index Sphinx, an infinite timeout occurs. Both from api and mysql client interface. Why is such a situation possible?
sphinx version 2.1.5.

Answer 1

There are two obvious questions here, why are you using an ancient version of the sphinx?
What prevents you from looking at the system logs and the sphinx and finding out for yourself?