Nginx + php-fpm + apc … compression

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I have a VPS running nginx 1.1.19, php-fpm 5.3.10, and APC 3.1.9. The server is primarily running PHP scripts (vB, SMF, IPB) I'm also using Cloudflare as a CDN if that matters.

From what I can tell, there are 3 options for compression and I'm not sure which are redundant with each other or if they all are and which service should be handling it.

nginix has gzip, php-fpm has zlib, and the PHP scripts themselves have gzip. I feel I've seen in a lot of documentation that if a web server (nginx) is handling gzip, the PHP scripts shouldn't. Should zlib in php-fpm be enabled along with gzip or are they technically the same thing? I saw one source that said gzip/mod_deflate with zlib_compression is redundant and unnecessarily using CPU cycles, but my vB installation seems to run smoother when zlib and gzip are both enabled.

Does anyone know of the most efficient combination/arrangement of compression for this setup?

Best Answer

I'm not sure what happens if you enable compression in multiple layers, but I would enable it in the topmost layer, i.e. Nginx. This catches dynamically produced PHP content, but also static content that is served directly by Nginx. I see compression as one of the final output filters before sending the content to the client.

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Found it..

It was because of apc.mmap_file_mask set into "straight file-backed mmap" like said oficial APC doc. Since server setup is multithreaded and apc was stored in fysical file, it was stucking by the reason of locked file.

Its very important to set it into shared memory.

So now my apc.ini is:

apc.gc_ttl="600"
apc.cache_by_default="1"
apc.filters = "apc\.php$,apc_clear\.php$"
apc.canonicalize="0"
apc.mmap_file_mask=/apc.shm.XXXXXX
apc.enable_cli="0"
apc.max_file_size = 5M
apc.report_autofilter="0"
apc.include_once_override="0"

apc.stat="0"

Nginx – MySQL, php-fpm, APC, Varnish and Nginx optimization for WordPress/W3 Total Cache

You have very good setup for your load. 20rps to php scripts is enough for 200k+ daily pageviews.

Things to tune for you are: innodb_buffer_pool_size = 10M - this is pretty small value. All your active data in innodb should fit to buffer pool, leaving enough space for transactional logs.

worker_connections 1024; - you can run out of this pretty fast. I'd suggest you to check nginx connections under real load using stubstatus module and tune this first few days your service will be running.

You may also increase php concurrency pm.max_children = 9 - to make use of extra RAM and CPU. Do it if you have problems with full tcp backlog (ss -nl)

You can hit max_children limit if you have high request rate and/or your scripts are slow enough. Increasing max working threads/processes will increase Load Average if your scripts is cpu-bound.

Let me show you the basic and approximate math. You have scripts that works 100ms and uses 5ms cpu time (100ms is disk/network IO wait) - in average.

If you have over 9*1000/100=90 requests per second your tcp backlog will start growing and new requests will wait some time until it will start.

Your scripts will consume 90*10/1000 = 45% cpu user time from single CPU core. Not much, ain't it?

If you increase max_children to 15 you may have 150 requests per second without slowing down, but scripts may consume 75% of single core cpu time.

It's good until you have too much load. If you will not have enough CPU or RAM to work with chosen concurrency - your server will hit Load average - it means that scripts will slow down due to CPU congestion. Server with Load Average values about 2-4 times of cpu core count usually is responsive enough. Requests processing will be somewhat slower, but you may handle higher request rate. If you will not have enough RAM - server will start swapping, loading disks and throttling CPU.

So, too few max_children - you will not handle high request rate. Too much - and your server will hang under high load.

Best Answer

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Nginx – MySQL, php-fpm, APC, Varnish and Nginx optimization for WordPress/W3 Total Cache

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