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Installs a callback which decides whether a statement is cached


(PECL mysqlnd_qc >= 1.0.0)

mysqlnd_qc_set_is_selectInstalls a callback which decides whether a statement is cached


mixed mysqlnd_qc_set_is_select ( string $callback )

Installs a callback which decides whether a statement is cached.

There are several ways of hinting PELC/mysqlnd_qc to cache a query. By default, PECL/mysqlnd_qc attempts to cache a if caching of all statements is enabled or the query string begins with a certain SQL hint. The plugin internally calls a function named is_select() to find out. This internal function can be replaced with a user-defined callback. Then, the user-defined callback is responsible to decide whether the plugin attempts to cache a statement. Because the internal function is replaced with the callback, the callback gains full control. The callback is free to ignore the configuration setting mysqlnd_qc.cache_by_default and SQL hints.

The callback is invoked for every statement inspected by the plugin. It is given the statements string as a parameter. The callback returns FALSE if the statement shall not be cached. It returns TRUE to make the plugin attempt to cache the statements result set, if any. A so-created cache entry is given the default TTL set with the PHP configuration directive mysqlnd_qc.ttl. If a different TTL shall be used, the callback returns a numeric value to be used as the TTL.

The internal is_select function is part of the internal cache storage handler interface. Thus, a user-defined storage handler offers the same capabilities.


This function has no parameters.

Return Values

Returns TRUE on success or FALSE on failure.


Example #1 mysqlnd_qc_set_is_select() example

/* callback which decides if query is cached */
function is_select($query) {
$patterns = array(
/* true - use default from mysqlnd_qc.ttl */
"@SELECT\s+.*\s+FROM\s+test@ismU" => true,
/* 3 - use TTL = 3 seconds */
"@SELECT\s+.*\s+FROM\s+news@ismU" => 3
/* check if query does match pattern */
foreach ($patterns as $pattern => $ttl) {
    if (
preg_match($pattern$query)) {
printf("is_select(%45s): cache\n"$query);
printf("is_select(%45s): do not cache\n"$query);

/* Connect, create and populate test table */
$mysqli = new mysqli("host""user""password""schema");
$mysqli->query("DROP TABLE IF EXISTS test");
$mysqli->query("CREATE TABLE test(id INT)");
$mysqli->query("INSERT INTO test(id) VALUES (1), (2), (3)");

/* cache put */
$mysqli->query("SELECT id FROM test WHERE id = 1");
/* cache hit */
$mysqli->query("SELECT id FROM test WHERE id = 1");
/* cache put */
$mysqli->query("SELECT * FROM test");

The above examples will output:

 is_select(     DROP TABLE IF EXISTS test): do not cache is_select(     CREATE TABLE test(id INT)): do not cache is_select( INSERT INTO test(id) VALUES (1), (2), (3)): do not cache is_select(    SELECT id FROM test WHERE id = 1): cache is_select(    SELECT id FROM test WHERE id = 1): cache is_select(       SELECT * FROM test): cache 

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