This package strives to be a way to memoize compilcated postgres queries in redis assuming one knows the output from postgresql will not change (frequently).

Configuration of the pgmemo server is done through a configuration file; this file is expressed in the JSON format. Allowable keys in the JSON file are any expressed in the libpq Connection String Parameter keywords. Values must be expressed as strings.

There are three other directives that are required in the configuration: redishost, redisport, and either zmq_bind or zmq_connect. redisport is the only value not represented as a string in the json configuration; it is an integer. redishost/port are the host and port that the redis server is listening on.

If you specify zmq_bind, the server will bind the zmq socket to the specified string. This is useful when you desire the pgmemo server to be the "non-moving part" in your architecture. When specifying zmq_connect, the socket is connected to the specified port. This is useful for systems where you want to have multiple pgmemo workers connecting to a central router (perhaps through MDP, etc).

Sample configuration file:

{
  "host": "8.8.8.8",
  "user" : "my_db_role",
  "password" : "my_password",
  "port" : "1234",
  "redishost" : "127.0.0.1",
  "redisport" : 6379,
  "zmq_bind" : "tcp://*:5555"
}

This uses a cmake based build system; from the source directory: mkdir build; cd build; cmake ..; make

As easy as /path/to/pgmemo configuration_file.

pgmemo uses a protocol buffer to perform it's communication. The required fields are the query field and the dbname field. If you want to force a refresh of the cache (after sending the cached value), you may set the refresh field to true. Example (C++):

  PGMemoRequest input;
  PGMemoRequest output;
  input.set_dbname("postgres");
  input.set_query("select clock_timestamp();");
  //send the input PGMemoRequest here
  //recieve into the output PGMemoRequest here
  std::cout << output.get_result_json() << std::endl; //JSON string of output
  //force a refresh
  input.set_refresh(true);
  //send the input PGMemoRequest here
  //recieve into the output PGMemoRequest here
  std::cout << output.get_result_json() << std::endl; //should be same as last result
  input.set_refresh(false);
  //send the input PGMemoRequest here
  //recieve into the output PGMemoRequest here
  std::cout << output.get_result_json() << std::endl; // Different result; refresh has been forced

If the query returns a single row, it is returned as a json string of a single document with col_name:value values. If there are multiple rows returned, the result is a json dictionary containing {rows: [{<row 1>}, {<row 2>},...]}.

This program requires the hiredis C bindings for redis and libpqxx, a protocol buffer library, as well as the FastBSON-Cpp and EasyZMQ-Cpp library. The prerequisites on a Debian/Ubuntu system may be installed with

sudo apt-get install libpqxx-dev libhiredis-dev libprotobuf-dev