Beyond TTL: user-defined storage

The query cache plugin supports the use of user-defined storage handler. User-defined storage handler can use arbitrarily complex invalidation algorithms and support arbitrary storage media.

All user-defined storage handlers have to provide a certain interface. The functions of the user-defined storage handler will be called by the core of the cache plugin. The necessary interface consists of seven public functions. Both procedural and object oriented user-defined storage handler must implement the same set of functions.

Please check the example for details.


<?php
/* Enable default caching of all statements */
ini_set("mysqlnd_qc.cache_by_default", 1);

/* Procedural user defined storage handler functions */

$__cache = array();

function get_hash($host_info, $port, $user, $db, $query) {
    global $__cache;
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());

    return md5(sprintf("%s%s%s%s%s", $host_info, $port, $user, $db, $query));
}

function find_query_in_cache($key) {
    global $__cache;
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());

    if (isset($__cache[$key])) {
        $tmp = $__cache[$key];
        if ($tmp["valid_until"] < time()) {
            unset($__cache[$key]);
            $ret = NULL;
        } else {
            $ret = $__cache[$key]["data"];
        }
    } else {
        $ret = NULL;
    }

    return $ret;
}

function return_to_cache($key) {
    /*
     Called on cache hit after cached data has been processed,
     may be used for reference counting
    */
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());
}

function add_query_to_cache_if_not_exists($key, $data, $ttl, $run_time, $store_time, $row_count) {
    global $__cache;
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());

    $__cache[$key] = array(
        "data"               => $data,
        "row_count"          => $row_count,
        "valid_until"        => time() + $ttl,
        "hits"               => 0,
        "run_time"           => $run_time,
        "store_time"         => $store_time,
        "cached_run_times"   => array(),
        "cached_store_times" => array(),
    );

    return TRUE;
}

function query_is_select($query) {
    printf("\t%s('%s'): ", __FUNCTION__, $query);

    $ret = FALSE;
    if (stristr($query, "SELECT") !== FALSE) {
        /* cache for 5 seconds */
        $ret = 5;
    }

    printf("%s\n", (FALSE === $ret) ? "FALSE" : $ret);
    return $ret;
}

function update_query_run_time_stats($key, $run_time, $store_time) {
    global $__cache;
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());

    if (isset($__cache[$key])) {
        $__cache[$key]['hits']++;
        $__cache[$key]["cached_run_times"][] = $run_time;
        $__cache[$key]["cached_store_times"][] = $store_time;
    }
}

function get_stats($key = NULL) {
    global $__cache;
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());

    if ($key && isset($__cache[$key])) {
        $stats = $__cache[$key];
    } else {
        $stats = array();
        foreach ($__cache as $key => $details) {
            $stats[$key] = array(
               'hits'              => $details['hits'],
               'bytes'             => strlen($details['data']),
               'uncached_run_time' => $details['run_time'],
               'cached_run_time'   => (count($details['cached_run_times']))
                                      ? array_sum($details['cached_run_times']) / count($details['cached_run_times'])
                                      : 0,
            );
        }
    }

    return $stats;
}

function clear_cache() {
    global $__cache;
    printf("\t%s(%d)\n", __FUNCTION__, func_num_args());

    $__cache = array();
    return TRUE;
}

/* Install procedural user-defined storage handler */
if (!mysqlnd_qc_set_user_handlers("get_hash", "find_query_in_cache",
    "return_to_cache", "add_query_to_cache_if_not_exists",
    "query_is_select", "update_query_run_time_stats", "get_stats", "clear_cache")) {
  
        printf("Failed to install user-defined storage handler\n");
}


/* Connect, create and populate test table */
$mysqli = new mysqli("host", "user", "password", "schema", "port", "socket");
$mysqli->query("DROP TABLE IF EXISTS test");
$mysqli->query("CREATE TABLE test(id INT)");
$mysqli->query("INSERT INTO test(id) VALUES (1), (2)");

printf("\nCache put/cache miss\n");

$res = $mysqli->query("SELECT id FROM test WHERE id = 1");
var_dump($res->fetch_assoc());
$res->free();

/* Delete record to verify we get our data from the cache */
$mysqli->query("DELETE FROM test WHERE id = 1");

printf("\nCache hit\n");

$res = $mysqli->query("SELECT id FROM test WHERE id = 1");
var_dump($res->fetch_assoc());
$res->free();

printf("\nDisplay cache statistics\n");
var_dump(mysqlnd_qc_get_cache_info());

printf("\nFlushing cache, cache put/cache miss");
var_dump(mysqlnd_qc_clear_cache());

$res = $mysqli->query("SELECT id FROM test WHERE id = 1");
var_dump($res->fetch_assoc());
$res->free();
?>

The above examples will output something similar to:

        query_is_select('DROP TABLE IF EXISTS test'): FALSE
        query_is_select('CREATE TABLE test(id INT)'): FALSE
        query_is_select('INSERT INTO test(id) VALUES (1), (2)'): FALSE

Cache put/cache miss
        query_is_select('SELECT id FROM test WHERE id = 1'): 5
        get_hash(5)
        find_query_in_cache(1)
        add_query_to_cache_if_not_exists(6)
array(1) {
  ["id"]=>
  string(1) "1"
}
        query_is_select('DELETE FROM test WHERE id = 1'): FALSE

Cache hit
        query_is_select('SELECT id FROM test WHERE id = 1'): 5
        get_hash(5)
        find_query_in_cache(1)
        return_to_cache(1)
        update_query_run_time_stats(3)
array(1) {
  ["id"]=>
  string(1) "1"
}

Display cache statistics
        get_stats(0)
array(4) {
  ["num_entries"]=>
  int(1)
  ["handler"]=>
  string(4) "user"
  ["handler_version"]=>
  string(5) "1.0.0"
  ["data"]=>
  array(1) {
    ["18683c177dc89bb352b29965d112fdaa"]=>
    array(4) {
      ["hits"]=>
      int(1)
      ["bytes"]=>
      int(71)
      ["uncached_run_time"]=>
      int(398)
      ["cached_run_time"]=>
      int(4)
    }
  }
}

Flushing cache, cache put/cache miss    clear_cache(0)
bool(true)
        query_is_select('SELECT id FROM test WHERE id = 1'): 5
        get_hash(5)
        find_query_in_cache(1)
        add_query_to_cache_if_not_exists(6)
NULL