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mysql_free_result — Gibt belegten Speicher wieder frei
mysql_free_result() gibt den Speicher frei, der mit der Ergebnis-Kennung assoziert ist.
Die Funktion muss nur dann aufgerufen werden, wenn Sie sich bei Anfragen, die große Ergebnismengen liefern, Sorgen über den Speicherverbrauch zur Laufzeit des PHP-Skripts machen. Nach Ablauf des Skripts wird der Speicher ohnehin freigegeben.
Gibt bei Erfolg TRUE zurück. Im Fehlerfall wird FALSE zurückgegeben.
Wird für den Parameter result ein Wert angegeben, der nicht vom Typ resource ist, wird ein Fehler der Stufe E_WARNING ausgegeben. Beachten Sie, dass mysql_query() nur eine resource für SELECT, SHOW, EXPLAIN und DESCRIBE Abfragen liefert.
Beispiel #1 Ein mysql_free_result() Beispiel
<?php
$result = mysql_query("SELECT id,email FROM people WHERE id = '42'");
if (!$result) {
echo 'Abfrage konnte nicht ausgeführt werden: ' . mysql_error();
exit;
}
/* Benutze result, unrer der Annahme wir sind hinterher damit fertig */
$row = mysql_fetch_assoc($result);
/* Nun geben wir den Speicher für result frei und fahren in unserem Skript fort */
mysql_free_result($result);
echo $row['id'];
echo $row['email'];
?>
Für Abwärtskompatibilität kann mysql_freeresult() verwendet werden. Diese Funktion ist jedoch veraltet.
Siehe auch mysql_query() und is_resource().
I agree with Joachim Kruyswijk (posted on 14-Jun-2005 11:42). I just did the test on my beta version of my new site (who needs to get dynamically news and user login from a database) and i use 1000kb less memory when i do not use mysql_free_result. I guess it is because the data it needs to load are not that large (for news: date, short description and for the user login: username, password). It may only be in the user control panel that it will be more, but since that isn't developed totally yet, i'll have to test :p
yes this function may increase the memory usage if you use unbuffered querys and if you have not fetched all the data from mysql. in this case the mysql api has a problem: you want to free the result but do not want to close the connection. now mysql will only accept another query if all data has been fetched, so the api now must fetch the rest of the data when calling mysql_free_result().
so only use unbuffered querys if you fetch all the data (and need it).
If you're seeing warnings like "Warning: Unknown: 6 result set(s) not freed. Use mysql_free_result to free result sets which were requested using mysql_query() in Unknown on line 0" and want to turn them off, set mysql.trace_mode = Off in your php.ini
ALWAYS use this function! I just encountered a bug in my code where I forgot to use this function. I also happen to be using mysql_pconnect() for a persistent connection. If you forget to free the result, it can hold the old result set open indefinitely within the HTTP process.
The upshot (in my application) was that I did updates that happened in a different HTTP process, but they mysteriously didn't show up in another HTTP process. After panicking that MySQL had mysterious data corruption and/or synchronization problems, I traced it back to this where an old result set was held open.
yes, i encountered that too. as far as i could tell, that's because the script is stored in memory after being compiled and that's as much more memory as it needs for a call to that function.
if you always get lotsa data in your results, using this function will decrease memory usage tho, unless you use non-buffered queries (which are preferable unless you absolutely *have* to use mysql_seek(), or you need to do another query while the last one hasn't finished reporting back, as they can provide a small speedup)
You not need to use this if you are using PHP 4.
The comment below this comment may explain why it's actually costing more memory.
Using this function may actually increase the amount of memory used. In my case, the script used 208 bytes less memory when *not* using mysql_free_result().
Check for yourself: call memory_get_usage() at the end of the script.
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