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Send an SQL query to MySQL, without fetching and buffering the result rows
(PHP 4 >= 4.0.6, PHP 5, PECL mysql:1.0)
Code Examples / Notes » mysql_unbuffered_querydavid
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. 14-jun-2003 06:35
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.
chabotc
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). shaner
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; } } } silvanojr
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. typer85
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, andre dot steffens
If you use mysql_ping() to check the connection, the resultset from mysql_unbuffered_query() will be kill.
steve_stockman
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
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
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 ... |
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