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POServer-Sent Events from PHP polling mySQL
 

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  1. POServer-Sent Events from PHP polling mySQL
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    <p>A back-office periodically needs to sent data to clients connected to a web application. Here is the script I have setup:</p> <pre><code>&lt;?php header("Content-Type: text/event-stream\n\n"); header('Cache-Control: no-cache'); flush(); ob_flush(); require_once('connect.php'); //connect to the database $mysql = mysql_connect($hostname, $username, $password) or die ('cannot reach database'); $db = mysql_select_db($database) or die ("this is not a valid database"); mysql_query("SET NAMES 'utf8'", $mysql); $query = mysql_query("SELECT * FROM `clientEvents` ORDER BY id DESC LIMIT 1") or die(mysql_error()); $row = mysql_fetch_array($query); $index = $row["id"]; echo $index; loop($index); function loop($index){ while (1) { ob_implicit_flush(true); $buffer = str_repeat(" ", 4096); echo $buffer."\n"; // Every second, look for new question. $query = mysql_query("SELECT * FROM `clientEvents` WHERE id&gt;$index ORDER BY id DESC LIMIT 1") or die(mysql_error()); $row = mysql_fetch_array($query); if(mysql_num_rows($query)&gt;0) { if($row["type"]=="pushCustomQuestion"){ pushCustomQuestion($row["data"],$row["id"]); break; } else if($row["type"]=="pushGameTimeEvent"){ pushGameTimeEvent($row["data"],$row["id"]); break; } } sleep(3); } function pushGameTimeEvent($id,$index) { //echo "id for game event:".$id; $result = mysql_fetch_array(mysql_query("SELECT * FROM game_events WHERE id = $id LIMIT 1")); //$num_results = mysql_num_rows($result); echo "event: new_game_event\n"; echo 'data: { "id": "' . $result['id'] . '",' .'"match_id": "' . $result['match_id'] . '",' .'"minute": "' . $result['minute'] . '",' .'"event_id": "' . $result['event_id'] . '",' .'"event_name": "' . $result['event_description'] . '",' .'"player_name": "' . $result['player1_name']. '",' .'"player2_name": "' . $result['player2_name'] . '",' .'"which_half": "' . $result['which_half'] . '",' .'"team_logo": "' . $result['team_logo'] . '"}'; echo "\n\n"; ob_flush(); flush(); sleep(10); loop($index); } </code></pre> <p>Everything seems to work OK up until seven clients load the web application where everything hogs. Is there something wrong with the script as it is?</p> <p>It seems to me that the way I'm doing it is counterintuitive since I'm polling the database in order to send a new event. Is there some other better way to trigger the event from the back- office application?</p> <p>Thanks for any help.</p>
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    1. USAris Brink
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    1. COI looks as if your apache allows only 7 open unanswered parallel connections, and your polling is not client-side, but the php as well as the html-connection stays open a long time.
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    2. CO@yvytty, the frequency is control with the sleep() method. Every 3 seconds it will let the loop continue where it checks the DB for a new entry.
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    3. CO@flaschenpost, indeed the connection stays open which is the way server-sent events work (unless I have misunderstood something)
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