zlib.output_compression On
zlib.output_compression_level 6
zlib.output_handler=

What should I add to zlib.output_handler= ?

In general usage, which one is better ? using zlib.output_compression On or output_hanlder = ob_gzhandler ?

And after setting this, may I turn on output_buffering ALSO ?

Thanks.

ob_gzhandler

You can still use output_buffering

http://www.php.net/manual/en/function.ob-gzhandler.php

ob_gzhandler just compresses the data