mysql_thread_id
@crazyone
as stated elsewhere, bear in mind that the MySQL API will still fetch all rows from MySQL when using the mysql_free_result() function. MySQL behaviour will not change through clientside coding.
So if you request a million rows while the first 50 rows suffice, then you still missed the point of unbuffered queries.
The manual is correct, you still need to fetch all rows from the result set whether you do it manually or through mysql_free_result(), the behaviour remains the same.
mysql_unbuffered_query
(PHP 4 >= 4.0.6, PHP 5)
mysql_unbuffered_query — 결과 행을 버퍼링하지도 인출하지도 않으면서 MySQL로 SQL 질의를 전송
설명
resource mysql_unbuffered_query
( string $query
[, resource $link_identifier
] )
mysql_unbuffered_query()는 SQL 질의를 결과 행들을 버퍼링하지도 인출하지도 않고 query 를 MySQL로 전송한다. 한편, 이는 거대한 결과 집합을 만드는 SQL 질의로 점유하는 메모리를 절약한다. 또한, 완료된 SQL 질의가 수행될 때까지 기다리지 않고, 첫행이 조회된 이후로 즉시 작업을 시작할 수 있다. 다중 DB-접속을 사용할 때, 옵션 인수인 link_identifier 를 지정해야한다.
인수
- query
-
SQL 질의문
- link_identifier
-
MySQL 연결. 지정하지 않으면 mysql_connect()로 연 마지막 연결을 사용합니다. 연결이 없으면, 인수 없이 mysql_connect()를 호출하여 연결을 만듭니다. 연결이 성립되지 않으면 E_WARNING 등급의 오류를 생성합니다.
반환값
SELECT, SHOW, DESCRIBE, EXPLAIN 구문에서 mysql_unbuffered_query()가 성공하면 resource를 에러가 발생하면 FALSE를 반환한다.
UPDATE, DELETE, DROP 등과 같은 SQL 구문에서 mysql_unbuffered_query()가 성공하면 TRUE를 에러가 발생하면 FALSE를 반환한다.
주의
Note: mysql_unbuffered_query()의 이점은 비용에서 온다: mysql_unbuffered_query()로부터 반환된 결과 집합은 mysql_num_rows()와 mysql_data_seek()에서 사용할 수 없다. 또한, MySQL로 새로운 SQL 질의를 전송하기 전에 비-버퍼링 SQL 질의로부터의 모든 결과 행을 인출해야한다.
add a note
User Contributed Notesmysql_unbuffered_query
markus at buyways dot nl
20-Aug-2008 08:51
20-Aug-2008 08:51
crazyone at crazycoders dot net
27-May-2008 04:47
27-May-2008 04:47
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.
Typer85 at gmail dot com
28-Dec-2006 12:33
28-Dec-2006 12:33
In response to "silvanojr at gmail dot com".
Your misunderstanding the point of this function. You MUST retrieve all rows in the result set BEFORE you issue another query.
Yes you can do a SQL_CALC_ROWS but that would mean you would have to query MySQL, thus either firing an error or deleting the previous query's result set as the new unbuffered result set would point to the result of the call to SQL_CALC_ROWS.
Keep that in mind folks,
silvanojr at gmail dot com
12-May-2006 09:02
12-May-2006 09:02
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
08-Oct-2004 01:18
08-Oct-2004 01:18
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
01-Apr-2004 10:19
01-Apr-2004 10:19
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.)
$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');
}
post at jfl dot dk
30-Nov-2003 01:57
30-Nov-2003 01:57
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.
14-Jun-2003 05:35
The other hand should really be, that the table remains locked until all rows have been retrieved, right? This is a very important thing to mention, you could tie up the whole database with a lock.
shaner at accretivetg dot com
21-May-2003 11:45
21-May-2003 11:45
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:
// 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;
}
}
}
frappyjohn at dos2linux dot org
18-Feb-2003 06:21
18-Feb-2003 06:21
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
18-May-2002 04:25
18-May-2002 04:25
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.
chabotc at reviewboard dot com
21-Aug-2001 09:21
21-Aug-2001 09:21
Stefan,
unbuffered query sends a query to the server, and does not first download the results before sending them to the end-user (php in this case).
So what it means is that -normaly- you could do this:
$res1 = mysql_query("select some",$db_conn);
while ($row = mysql_fetch_row($res)) {
$res2 = mysql_query("select some other",$db_conn);
// do some other stuff
}
With an unbuffered query you could NOT do this, the result set from $res1 would be LOST on the second query.
However, it does not mean you -have- to fetch all rows ... just that the API does not save the result set in memory for you.
However, when using different db connections, it all works ofcource ...
For more information, please refer to the mysql manual, they have a lot of docs on query & unbuffered queries (the php api is just a basic wrapper around there native api's).