[UPHPU] script timers

[Mac Newbold]

Today at 10:25am, Dave Smith said:

> First, be sure to disable any output buffering. Then, use logging on the 
> server side to do time stamping. Write timestamps to a file on disk as the 
> PHP script executes. Lastly, start looking at your Apache (or whatever web 
> server) logs, and see if there are any errors there that could be causing the 
> problem. It's most likely a problem with the web server itself, and not your 
> PHP code.

That's great advice. The error_log() function comes in really handy for 
that. If you're looking for good places to add the timers, here are some 
ideas:

1. Before and after database queries, especially big ones
2. Before and after loops with many iterations
3. Inside a loop with fewer iterations
4. As close as possible to the start and end of the script
5. Before and after any include() or require() calls
6. Before and after any function or method calls that might be significant

If you start out up at the top with something like this:

$timechk=0; error_log("timecheck $timechk: ".date()); $timechk++;

Then sprinkle these throughout your code:

error_log("timecheck $timechk: ".date()); $timechk++;

They're easy to find and comment out or remove later if you want. If you 
want to make them easily reusable, set up a variable called $PROFILE or 
something, that is 0 or 1, then use this instead:

if ($PROFILE) { error_log("timecheck $timechk: ".date()); $timechk++; }

Then you can turn them all on or off at once, turn some of them on, etc.

Once you've got all the timechecks in place, you can see where the big 
gaps are, and investigate why they're so big by narrowing down the space 
between checks if necessary. If you wanted to get more fancy, you could 
have the script check the difference between the checkpoint times, and 
only tell you about ones that were above 0.2 seconds or something. It also 
can be helpful to add extra output at each checkpoint so that it tells you 
where it is, rather than just uniquely numbering each of them.

Most of the time when I've done this, it turns out to be a database query 
that is either doing the wrong join or is missing an index in the database 
that would speed it up immensely. Sometimes it is a loop that is iterating 
way more than you intended, or other stuff. Dave is right about the 
server: check memory usage on the server while the script is running. The 
default memory limit for a PHP script is 8MB, but if you've bumped that 
higher, you may be using up all the physical RAM so that it is swapping to 
disk in a nasty thing called thrashing, which will kill your performance.

Thanks,
Mac

> Daniel wrote:
>> There is serious latency from the time someone pushes a button on our
>> webpages and the time the following page is displayed.  I would like
>> to know how to pin point the bottle neck.  We date stamped the second
>> page at the beginning of the script and at the end and subtracted the
>> two times to get a sub-second period.  For some reason the page takes
>> a few seconds to come up.  Where could there be a bottle neck and how
>> can we find out exactly where it is?

--
Mac Newbold		MNE - Mac Newbold Enterprises, LLC
mac at macnewbold.com	http://www.macnewbold.com/