A minimal communication protocol is implented, using the LISTEN/NOTIFY facility provided by postgres, which is used by the powa-web project. You can send queries to collector by sending messages on the “powa_collector” channel. The collector will send answers on the channel you specified, so make sure to listen on it before sending any query to not miss answers.

The requests are of the following form:


  • COMMAND: mandatory argument describing the query. The following commands are supported:
    • RELOAD: reload the configuration and report that the main thread successfully received the command. The reload will be attempted even if no response channel was provided.
    • WORKERS_STATUS: return a JSON (srvid is the key, status is the content) describing the status of each remote server thread. Command is ignored if no response channel was provided. This command accept an optional argument to get the status of a single remote server, identified by its srvid. If no worker exists for this server, an empty JSON will be returned.
  • RESPONSE_CHANNEL: mandatory argument to describe the NOTIFY channel the client listens a response on. ‘-‘ can be used if no answer should be sent.
  • OPTIONAL_ARGUMENTS: space separated list of arguments, specific to the underlying command.

The answers are of the form:


  • COMMAND: same as the command in the query
  • STATUS: OK or KO.
  • DATA: reason for the failure if status is KO, otherwise the data for the answer.