Finding cache candidates
A statement should be considered for caching if it is executed often and has a long run time. Cache candidates are found by creating a list of statements sorted by the product of the number of executions multiplied by the statements run time. The function mysqlnd_qc_get_query_trace_log() returns a query log which help with the task.
Collecting a query trace is a slow operation. Thus, it is disabled by default. The PHP configuration directive mysqlnd_qc.collect_query_trace is used to enable it. The functions trace contains one entry for every query issued before the function is called.
Example #1 Collecting a query trace
mysqlnd_qc.enable_qc=1 mysqlnd_qc.collect_query_trace=1
<?php
/* connect to MySQL */
$mysqli = new mysqli("host", "user", "password", "schema", "port", "socket");
/* dummy queries to fill the query trace */
for ($i = 0; $i < 2; $i++) {
$res = $mysqli->query("SELECT 1 AS _one FROM DUAL");
$res->free();
}
/* dump trace */
var_dump(mysqlnd_qc_get_query_trace_log());
?>
The above examples will output:
array(2) {
[0]=>
array(8) {
["query"]=>
string(26) "SELECT 1 AS _one FROM DUAL"
["origin"]=>
string(102) "#0 qc.php(7): mysqli->query('SELECT 1 AS _on...')
#1 {main}"
["run_time"]=>
int(0)
["store_time"]=>
int(25)
["eligible_for_caching"]=>
bool(false)
["no_table"]=>
bool(false)
["was_added"]=>
bool(false)
["was_already_in_cache"]=>
bool(false)
}
[1]=>
array(8) {
["query"]=>
string(26) "SELECT 1 AS _one FROM DUAL"
["origin"]=>
string(102) "#0 qc.php(7): mysqli->query('SELECT 1 AS _on...')
#1 {main}"
["run_time"]=>
int(0)
["store_time"]=>
int(8)
["eligible_for_caching"]=>
bool(false)
["no_table"]=>
bool(false)
["was_added"]=>
bool(false)
["was_already_in_cache"]=>
bool(false)
}
}
Assorted information is given in the trace. Among them timings and the origin of the query call. The origin property holds a code backtrace to identify the source of the query. The depth of the backtrace can be limited with the PHP configuration directive mysqlnd_qc.query_trace_bt_depth. The default depth is 3.
Example #2 Setting the backtrace depth with the mysqlnd_qc.query_trace_bt_depth ini setting
mysqlnd_qc.enable_qc=1 mysqlnd_qc.collect_query_trace=1
<?php
/* connect to MySQL */
$mysqli = new mysqli("host", "user", "password", "schema", "port", "socket");
$mysqli->query("DROP TABLE IF EXISTS test");
$mysqli->query("CREATE TABLE test(id INT)");
$mysqli->query("INSERT INTO test(id) VALUES (1), (2), (3)");
/* dummy queries to fill the query trace */
for ($i = 0; $i < 3; $i++) {
$res = $mysqli->query("SELECT id FROM test WHERE id = " . $mysqli->real_escape_string($i));
$res->free();
}
$trace = mysqlnd_qc_get_query_trace_log();
$summary = array();
foreach ($trace as $entry) {
if (!isset($summary[$entry['query']])) {
$summary[$entry['query']] = array(
"executions" => 1,
"time" => $entry['run_time'] + $entry['store_time'],
);
} else {
$summary[$entry['query']]['executions']++;
$summary[$entry['query']]['time'] += $entry['run_time'] + $entry['store_time'];
}
}
foreach ($summary as $query => $details) {
printf("%45s: %5dms (%dx)\n",
$query, $details['time'], $details['executions']);
}
?>
The above examples will output something similar to:
DROP TABLE IF EXISTS test: 0ms (1x)
CREATE TABLE test(id INT): 0ms (1x)
INSERT INTO test(id) VALUES (1), (2), (3): 0ms (1x)
SELECT id FROM test WHERE id = 0: 25ms (1x)
SELECT id FROM test WHERE id = 1: 10ms (1x)
SELECT id FROM test WHERE id = 2: 9ms (1x)
English translation
You have asked to visit this site in English. For now, only the interface is translated, but not all the content yet.If you want to help me in translations, your contribution is welcome. All you need to do is register on the site, and send me a message asking me to add you to the group of translators, which will give you the opportunity to translate the pages you want. A link at the bottom of each translated page indicates that you are the translator, and has a link to your profile.
Thank you in advance.
Document created the 30/01/2003, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/php-rf-mysqlnd-qc.cache-candidates.html
The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.
References
These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.
