define('SAVEQUERIES', true) = debug_backtrace() = Error 500

[ozh]

This won't stop the earth rotation, but I've come across an annoying bug that I'm having difficulties to identify precisely.

Fact:
define('SAVEQUERIES', true); in my wp-config.php makes everything break with an Error 500.

Symptoms:
Error 500, log says "Premature end of script headers: /dh/cgi-system/php5.cgi" which means basically anything.

Culprit:
Function get_caller() in wp-db.php is the one causing the error. In that function, this particular line is to blame: $bt = debug_backtrace();
No clue why debug_backtrace() break things, though, and @debug_backtrace() doesnt help.

Server specs:
PHP 5.2.3, Apache running CGI/FastCGI, ​whole phpinfo()

This ticket is mostly for the record if anyone happens to search here for the same problem, even if it's going to get a wontfix/worksforme/cantreproduce. Cheers :)

[tellyworth]

A bit of googling suggests Zend Optimizer might cause debug_backtrace() to trigger a 500 error on CGI servers. Can you test with that disabled?

[ozh]

I don't have access to php.ini so I guess I can't ...

[ryan]

Milestone 2.5.2 deleted

[mrmist]

Can't reproduce, with zend / php 5.2.5 / cgi

Not exactly the same config I grant, but it doesn't seem to "break everything".

[jacobsantos]

This belongs on the support forums until it is known what in WordPress is causing the problem if anything. Most likely a bug in PHP executable or something. Anything done in WordPress at the moment will only mask the real issue.