iBlog - Ilia Alshanetsky - Comments

Mike: PHP's Output Buffering

nospam@example.com (Mike) — Mon, 12 Dec 2011 05:12:28 -0500

How about a PHP_OUTPUT_HANDLER_ABSORBENT flag for trunk?

ob_start(null, 1024, PHP_OUTPUT_HANDLER_STDFLAGS | PHP_OUTPUT_HANDLER_ABSORBENT);

Though, due to current implementation, PHP_OUTPUT_HANDLER_ALIGN_TO_SIZE, i.e. 4k, is the allocation barrier.

gphilip: PHP's Output Buffering

nospam@example.com (gphilip) — Mon, 12 Dec 2011 03:56:48 -0500

Hi,

"What was unusual is that 16 calls to ob_start() up chewing through almost 700kb of memory"

Can you give more information please under what circumstances it happened?

http://pastebin.com/XPhtzpAh

I think ob_get_clean takes care of freeing the memory right away, so an ob_call in one request can result in max 40kB "extra peak", which is nothing in case of a regular webapplication.

Ilia Alshanetsky: PHP's Output Buffering

nospam@example.com (Ilia Alshanetsky) — Thu, 08 Dec 2011 11:49:06 -0500

In PHP 5.4 the default buffer size was reduced to 0x4000 (16kb), which in part is responsible for the performance improvement.

5.4 still suffers from the limitation that you cannot specify a custom buffer size, and have it be automatically increased when the data in the buffer exceeds the buffer size.

Chris Jones: PHP's Output Buffering

nospam@example.com (Chris Jones) — Thu, 08 Dec 2011 10:00:19 -0500

An error is thrown in PHP 5.4 but not PHP 5.3:

$ cat t.php

$ php54 t.php
PHP Warning: ob_start(): no array or string given in /tmp/t.php on line 3

Ilia's patch to PHP 5.3 allowed the first parameter to be overloaded.

Chris Jones: PHP's Output Buffering

nospam@example.com (Chris Jones) — Thu, 08 Dec 2011 09:55:39 -0500

For people not following PHP development, output buffering changed a lot in PHP 5.4. Running this:

$a = microtime(1);
for ($i = 0; $i < 100000; $i++) {
ob_start();
echo str_repeat("a", 1024);
ob_end_clean();
}
var_dump(microtime(1) - $a);
echo memory_get_peak_usage(true), "\n";

against an unpatched PHP 5.3 and PHP 5.4 gives:

$ php53 test.php
float(0.66586494445801)
524288
$ php54 test.php
float(0.29983496665955)
262144

Sebastian: PHP's Output Buffering

nospam@example.com (Sebastian) — Thu, 08 Dec 2011 06:04:14 -0500

I dont understand your post because the first parameter for ob_start is not the chunk size, it is the callback function. It seems to be that ob_start doest not throw a error if callback is not valid.

Example: ob_start('asdf'); (function not av.)

Ilia Alshanetsky: PHP's Output Buffering

nospam@example.com (Ilia Alshanetsky) — Thu, 08 Dec 2011 05:21:10 -0500

You can try the test at:
http://pastebin.com/Kjpmea3h

in this test the new code is about 25% faster, not to mention more memory efficient.

Ilia Alshanetsky: PHP's Output Buffering

nospam@example.com (Ilia Alshanetsky) — Thu, 08 Dec 2011 04:19:23 -0500

Think of a templating system that needs to generate various sub-templates and place resulting data in various different sections of the page.

Ilia Alshanetsky: PHP's Output Buffering

nospam@example.com (Ilia Alshanetsky) — Thu, 08 Dec 2011 04:10:57 -0500

There is a really good reason why it is slower. Your text is quite big, but you set your initial buffer size to mere 1kb, so PHP needs to keep resizing the buffer resulting in a slow down due to memory re-allocation. If you set the initial to a size more reflective of your output size you will see a performance benefit.

As it stands you have a text size that is 3.2kb in size that you display 50 times for a total of 150+kb. With default allocation schema there are 12 re-allocations, with 1kb buffer there are 150 (10x more), hence the speed drop.

Ilia Alshanetsky: PHP's Output Buffering

nospam@example.com (Ilia Alshanetsky) — Thu, 08 Dec 2011 04:05:30 -0500

You are correct, it should say 10kb not 20... I'll adjust.

Sebastian: PHP's Output Buffering

nospam@example.com (Sebastian) — Thu, 08 Dec 2011 02:20:44 -0500

Hi! i've tested this with a little script: http://pastebin.com/w27a5MXP

Seems that the execution time increase if you set the chunk size.

Tests
- without chunk size ~0.1 ms
- with chunk size ~2.0 ms

But test it your self

Evan: PHP's Output Buffering

nospam@example.com (Evan) — Wed, 07 Dec 2011 19:50:38 -0500

Co solution but what is he use-case for using ob so extensively?

Sam Hennessy: PHP's Output Buffering

nospam@example.com (Sam Hennessy) — Wed, 07 Dec 2011 19:08:23 -0500

Thanks for the post! Maybe I'm reading it wrong, but the snippet for the block size says 10*1024, but in the body of the post you say the block size is 20 kb.

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Ilia Alshanetsky: New PHP-Excel (0.9.5) was just released!

nospam@example.com (Ilia Alshanetsky) — Fri, 07 Oct 2011 14:00:12 -0400

From what I can tell in the discussion, the errors are based on library and/or headers not being in the path.