-- 
-- the procedure
--

DROP PROCEDURE IF EXISTS cachedata;

DELIMITER $$
CREATE PROCEDURE cachedata(
  IN obj_id BIGINT UNSIGNED,
  IN start  DATETIME,
  IN end    DATETIME
)

cachedata:BEGIN
  DECLARE cache_count BIGINT;

  SET @timestamp := NOW();

  CREATE TEMPORARY TABLE IF NOT EXISTS cachedata (
    timestamp    DATETIME,
    object_id    BIGINT UNSIGNED NOT NULL,
    start        DATETIME,
    end          DATETIME,
    seqno        BIGINT AUTO_INCREMENT,
    value        FLOAT,
    PRIMARY KEY (seqno),
    INDEX (timestamp),
    INDEX (object_id, start, end)
  ) ENGINE=INNODB;

  DELETE FROM cachedata WHERE
    timestamp < DATE_SUB(@timestamp, INTERVAL 15 SECOND);

  SELECT count(*) INTO cache_count FROM cachedata WHERE
    object_id = obj_id
    AND start = start
    AND end = end;

  IF cache_count > 0 THEN LEAVE cachedata;
  END IF;

  -- some fake cache
  INSERT INTO cachedata (timestamp, object_id, start, end, value) VALUES
    (@timestamp, obj_id, start, end, 1234),
    (@timestamp, obj_id, start, end, 4567),
    (@timestamp, obj_id, start, end, 8901),
    (@timestamp, obj_id, start, end, 1234),
    (@timestamp, obj_id, start, end, 4567),
    (@timestamp, obj_id, start, end, 8901),
    (@timestamp, obj_id, start, end, 1234),
    (@timestamp, obj_id, start, end, 4567),
    (@timestamp, obj_id, start, end, 8901),
    (@timestamp, obj_id, start, end, 1234),
    (@timestamp, obj_id, start, end, 4567),
    (@timestamp, obj_id, start, end, 8901),
    (@timestamp, obj_id, start, end, 2345),
    (@timestamp, obj_id, start, end, 1234),
    (@timestamp, obj_id, start, end, 4567),
    (@timestamp, obj_id, start, end, 8901),
    (@timestamp, obj_id, start, end, 2345),
    (@timestamp, obj_id, start, end, 1234),
    (@timestamp, obj_id, start, end, 4567),
    (@timestamp, obj_id, start, end, 8901),
    (@timestamp, obj_id, start, end, 2345);

END$$

-- 
-- the function
--

DROP FUNCTION IF EXISTS get_cache$$

CREATE FUNCTION get_cache(
  obj_id   BIGINT UNSIGNED,
  start    DATETIME,
  end      DATETIME
)
  RETURNS FLOAT
  READS SQL DATA
BEGIN
  DECLARE result FLOAT;

  CALL cachedata(obj_id, start, end);

  -- calculate something

  SELECT SUM(value) INTO result FROM cachedata WHERE
    object_id = obj_id
    AND start = start
    AND end = end;

  RETURN result;
END$$

DELIMITER ;

--
-- INSTRUCTIONS
--

-- import the FUNC and PROC above

-- run a query:
SELECT get_cache(1, '2014-01-01', '2014-02-01');

-- now wait a bit, from 15-60 seconds in my tests
-- then rerun the query

-- MySQL crashes