mysql_thread_id
You are NOT required to read all rows from the resultset when using unbuffered query, you may opt out at any time and use mysql_free_result. Imagine looking at 1 million row when the first 50 suffice? Just free the result and you are good to go again.
mysql_unbuffered_query
(PHP 4 >= 4.0.6, PHP 5)
mysql_unbuffered_query — Invia una query SQL a MySQL senza caricare e bufferare le righe risultanti
Descrizione
resource mysql_unbuffered_query
( string
$query
[, resource $identificativo_connessione
[, int $modo_risultato
]] )
mysql_unbuffered_query() invia una query SQL
query a MySQL senza caricare e
bufferare le righe risultanti automaticamente come fa
mysql_query(). Da una parte, questo
risparmia un considerevole quantità di memoria con le query SQL che
producono risulati di grandi dimensioni. Dall'altra parte, si può iniziare
l'elaborazione dei risultati immediatamente dopo che la prima riga
è stata recuperata: non si deve attendere finché la query SQL
sia completamente eseguita. Quando si usano diverse connessioni a database,
si deve specificare il paramentro opzionale
identificativo_connessione.
Il parametro opzionale modo_risultato
può essere MYSQL_USE_RESULT e MYSQL_STORE_RESULT. Il valore
predefinito è MYSQL_USE_RESULT, quindi il risultato non è bufferato.
Vedere anche mysql_query() per la
controparte di questo comportamento.
Nota:
I benefici di mysql_unbuffered_query() hanno un costo: non si può usare mysql_num_rows() su un risultato restituito da mysql_unbuffered_query(). Inoltre si debbono caricare tutte le righe risultanti da una query SQL non bufferata prima di poter inviare una nuova query SQL a MySQL.
vedere anche: mysql_query().
add a note
User Contributed Notes
mysql_unbuffered_query - [9 notes]
crazyone at crazycoders dot net ¶
4 years ago
shaner at accretivetg dot com ¶
10 years ago
Regarding bailing on a really large result, while doing an unbuffered query, there _is_ a way to do this: kill the thread and exit your processing loop. This, of course, requires having a separate database link. Something like below does the trick:
<?php
// a db link for queries
$lh = mysql_connect( 'server', 'uname', 'pword' );
// and a controller link
$clh = mysql_connect( 'server', 'uname', 'pword', true );
if ( mysql_select_db ( 'big_database', $lh ) )
{
$began = time();
$tout = 60 * 5; // five minute limit
$qry = "SELECT * FROM my_bigass_table";
$rh = mysql_unbuffered_query( $qry, $lh );
$thread = mysql_thread_id ( $lh );
while ( $res = mysql_fetch_row( $rh ) )
{
/* do what you need to do
* ...
* ...
*/
if ( ( time() - $began ) > $tout )
{
// this is taking too long
mysql_query( "KILL $thread", $clh );
break;
}
}
}
?>
post at jfl dot dk ¶
9 years ago
If using optimized MyISAM tables I guess there is a big advantage with this function as it is possible to do selects and inserts on the same time as long as no rows in the table gets updated.
frappyjohn at dos2linux dot org ¶
10 years ago
Don't let the two hands confuse you, these are both advantages (they should really be on the same hand):
On the one hand, this saves a considerable amount of memory with SQL queries that produce large result sets.
On the other hand, you can start working on the result set immediately ...
david at php dot net ¶
11 years ago
You are absolutely required to retrieve all rows in the result set (option 'a' in the first comment). If you fail to do so, PHP will do so for you, and will emit a NOTICE warning you of the fact. From the MySQL API, "Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for. ".
Also note that if you are using this function, you should be quick about processing the result set, or you will tie up the MySQL server (other threads will be unable to write to the tables you are reading from).
If you want to be able to 'abort' mid result-set or if you want to do lengthy processing on the results, you are misunderstanding the purpose of this function.
Also note that UPDATE queries etc return no result set, so this function is only useful for SELECT etc.
silvanojr at gmail dot com ¶
7 years ago
Note: The benefits of mysql_unbuffered_query() come at a cost: You cannot use mysql_num_rows() and...
but it looks like you can use SQL_CALC_ROWS on MySQL to get the total rows without the limit.
andre dot steffens at adress-research dot de ¶
8 years ago
If you use mysql_ping() to check the connection, the resultset from mysql_unbuffered_query() will be kill.
steve_stockman at mac dot symantec dot com ¶
9 years ago
If you are going to do a large query, but are concerned about blocking access to the table during an unbuffered query, why not go through a temporary table? (Of course, this is predicated on the current user having permission to create tables.)
<?php
$dbQuery = "SELECT something ...";
if (mysql_query ("CREATE TEMPORARY TABLE MyQuery $dbQuery")) {
$numRows = mysql_affected_rows();
if ($numRows == 0) {
/* handle empty selection */
} else {
$result = mysql_unbuffered_query ('SELECT * FROM MyQuery');
/* handle result */
}
mysql_query ('DROP TABLE MyQuery');
}
?>