Life cycle of a PHP request?

Anon

Could someone discuss the life cycle of a request for a PHP document? I'm specifically interested in knowing at what point headers are sent out, and what might cause a request to end.

My problem is blank documents (as indicated by Netscape's document-contained-no-data error) in PHP docs that update a mySQL table. I'm guessing an error is killing execution--that headers are sent and the connection is closed before output statements are reached.

Knowing more about what's going on under the hood could help me in a lot of ways.
Thanks!

Anon

I can't answer your question exactly. As far as I understand, apache or your php cgi module starts parsing the script when the request is made and doesn't stop until the script is finished, the user aborts, or it times out for one reason or another. The header is sent whenever anything at all is sent back to the user. If the first second of script execution has no output then the client will still be waiting for a response. (That COULD be wrong.)
Anyways... if you're having connection problems, I'd advise you check out the connection handling page in the PHP manual:
http://www.php.net/manual/features.connection-handling.php

Anon

One thing you should always be doing is checking the value returned by any query, and if it's 0, then have some way of echoing or printing the error to the browser (if you're developing) or (if it's production code) showing a nice "ooops, sorry, something messed up" message to the user and logging the error returned by the db.

e.g.

if (!$result = mysql_query($sql)) {
die("Error: " . mysql_error($db_handle));
}

This will cut down on those pesky "document contained no data" errors at least; if you rewrite your code (or if you already have something like this in place) and the problem persists, then post your problem here again with more info.

HTH