PHP Performance tuning for Drupal 8

©2016 Acquia Inc. — Confidential and Proprietary
Erin Rasmussen, Support Engineer,
Acquia
PHP Performance
Tuning
for Drupal 8

Make that Drupal 8 site fly!!
– Brief glance over Best Practices for Performance
Tuning.
– PHP tuning including Opcache, Interned strings and
apcu
– Varnish, Memcache, and Database tips
– The Software Stack, with Drupal 8 integration tips.

Mitigate against Failure by planning for Success!!
– Test, test and then Test again! (Include Load & Security
Testing!)
– Performance Review is Key: Understand the factors
that Affect your Site’s Performance
– Incorporate these strategies in your Continuous
Improvement Process
We want your project to succeed as much as you do!

This is an example stack, there
are multiple ways configure
them, your software may be
different.
Note: Development environments are
almost always Different than
Production environments.
Know the Stack, Love the Stack
Balancer / Varnish
Memcached
Apache PHP/FPM
MySQL
File System
Code Repo

Multi-Tier, the Stack gets bigger
With multi-tier, these the
software stack can be split
among server instances.
With redundancy and
failover.
Balancer / Varnish
Balancer / Varnish
Memcached
Apache PHP/FPM
Apache PHP/FPM
MySQL & File System
MySQL & File System
Code Repo
Server AMI Type #Cores Date Time 1m 5m 15m
bal-1*5*8 m3.2xlarge 8 2017-02-20 00:08:21 0.00 0.03 0.08
bal-1*5*9 m3.2xlarge 8 2017-02-20 00:08:22 0.33 0.29 0.25
web-18**7 c3.large 2 2017-02-20 00:08:21 0.02 0.03 0.05
web-18**8 c3.large 2 2017-02-20 00:08:21 0.00 0.01 0.05
fsdb-1**25 c3.large 2 2017-02-20 00:08:22 0.07 0.05 0.05
fsdb-1**26 c3.large 2 2017-02-20 00:08:23 0.03 0.04 0.05

Balancers / Caching a short intro
Drupal 7, has URL-based page caching
and empties the page cache for every edited piece of content!
2009-2011 Varnish wasn’t widely used, so Drupal 7 caches
pages, but doesn’t invalidate them intelligently.
Cache-Control = public, max-age=300
Works great – until there’s a DDOS or back-end server issue
Cache-Control = public, max-age=31536000
Works great – until content updates aren’t reflected on the site.

Drupal 8 Caching is re-architected
• Has a proper internal cache API, allows tagging of cache
items.
• Each single item is described with tags.
Tags "bubble" up to all rendering parents.
These tags are stored in the cache API.
Cache::invalidateTags(["tag"])
CacheTagsListenersInterface
The content API's call ::invalidateTags().
The render and page caches are transparently invalidated.

Varnish https://varnish-cache.org
Support for Drupal 8 Cache Tags with Varnish
Acquia Purge for Drupal 8 is a fully-featured API
and you plug in a 'purger' to it, to support your CDN

PHP / FPM http://php.net https://php-fpm.org
– Memory Limits
– Max Execution Time
– Zend OPcache
– APC user cache
– Memory Allocation Math

PHP Memory Limit http://php.net/manual/en/ini.core.php#ini.memory-
limit
The PHP memory_limit is the maximum number of M (in
integers) that a single PHP/FPM proc can consume, by
default memory_limit =128M
Clear signs this is set too low:
– php-errors.log: [20-Feb-2017 19:26:10 America/New_York] PHP Fatal error: Allowed memory
size of 268435456 bytes exhausted (tried to allocate 15990062 bytes) in
docroot/includes/database/database.inc on line 2227
– PHP WSOD errors or “Temporarily Unavailable” errors.

Max Execution Time
http://php.net/manual/en/features.connection-handling.php
The amount of time a single PHP process can run (in
seconds) max_execution_time
– Resolve this problems by identifying slow processes
and resolving the request or set_time_limit() function.
Clear signs that your processes are taking too long
–fpm-error.log max_children errors
–White Screen of Death (Temporary Unavailable) errors.

OPcache (opcode cache) http://php.net/manual/en/intro.opcache.php
Caches pre-compiled bytecode. Faster than using PHP of
load & parse each script for each & every HTTP request.
key variable: opcache.memory_consumption(128M)
Needs to be large enough to store compiled code for your
applications PHP scripts Clear sign that this is too small:
– php-errors.log Warning: require_once() [function.require-once]: Unable to allocate memory for
pool.
OPcache Status monitor: https://github.com/rlerdorf/opcache-status

OPcache http://php.net/manual/en/book.opcache.php
Interned Strings - the amount of memory (M) used to store
identical strings (detected by PHP). By default this is a shared
buffer allowing all Drupal PHP processes to reference it across multiple
PHP/FPM procs - saving memory.
Clear sign that this is set too low:
– Fpm-error.log: Warning Interned string buffer overflow
More indepth information:
http://jpauli.github.io/2015/03/05/opcache.html

APC User Cache http://php.net/manual/en/intro.apcu.php
APC User cache is PHP APC minus OPcache, rarely
used in Drupal 7 (apc.shm_size= 8M is ok), increase for
Drupal 8 (apc.shm_size=16 or 32M)
Clear sign that the APC User cache is set too small:
– In php-errors.log : [20-Feb-2017 13:54:16 America/New_York] PHP Warning: apcu_store(): Unable to allocate
memory for pool. in /mnt/www/html/somenamedev/docroot/core/lib/Drupal/Core/Cache/ApcuBackend.php on line
177
Get usage Details!: use apc.php script in the docroot and
view in your browser: note: the charts are less accurate than the text

APC User Cache
Drupal 8.3 will reduce the amount stored in APC user
cache in response to community issues:
– Rationalize use of the 'discovery' cache bin, since it's stored in the limited
size APCu by default https://www.drupal.org/node/2765271
– Change ViewsData to use the default cache bin instead of discovery
https://www.drupal.org/node/2824547

PHP Procs and PHP Memory Math
Total RAM 3860
OS 50
MySQL 1930
Memcache 64
Sites 4
Sitename Memory Limit Opcache APCu FPM
d7sitedev 256 128 8 1
d7sitestg 256 128 8 1
d8sitedev 128 96 16 1
d8sitestg 128 96 16 1
Calculate the available
memory for PHP
(Total - OS - MySQL -Memcache )
Memory use by 1 Process:
– Use top
– memory_get_peak_usage()
– Devel (Drupal 7 & 8)
Calculate how many procs
you can afford.

PHP/FPM max_children errors
When there are more incoming requests than PHP/FPM
can handle you get max_children errors.
Clear sign that the site is exhausting PHP/FPM procs:
– fpm-error.log srv-**35m notice [22-Feb-2017 16:32:38] WARNING: [pool someuser]
server reached max_children setting (27), consider raising it.
Causes are Varied – Large amount of HTTP traffic,
PHP/FPM procs that are looping, or not terminating effectively. Or calls to External Services
hanging/timing out

Adding the Impact of Traffic
What happens when the new site launches – or it gets
retweeted a million times:

What’s in that Traffic?

Memcached https://memcached.org
Is a open source, high-performance, distributed memory object caching system
Drupal 8 Memcache Module is Alpha
https://www.drupal.org/project/memcache
The Drupal 8 module will make GETS and SETS with
properly configured Memcached, and supports
key_prefixing.
However, Memcached slabs are not encrypted by default
Community Development is needed for a Stable Release
of the Memcahed Drupal modue

Keep the Database Layer Happy
– Enable Syslog, disable database Watchdog Logging.
– Caching to the Database does not always Scale, keep
an eye on your capacity and I/O errors.
– Optimize queries, and keep an eye on database tables.
Even the most efficient Views query will be slow on a 50 Gb table.

Keep the Front End Performant
– Compress Site Images, PDFs and other Files before
uploading them to the site. (Even a cached 7MB photo is a major
performance hog when used 27 times on a site.)
– Compress your CSS, and minify your JS.
– Keep an eye on External calls. Use timeouts, and allow your
application to fail gracefully when those resources cannot be reached.

Thank you!  Drupal
✩ Modern PHP: New Features and Good Practices by
Josh Lockhart http://shop.oreilly.com/product/0636920033868.do
✩ Drupal 8 Cache API https://www.drupal.org/docs/8/api/cache-api/cache-
api
✩ Acquia Purge https://www.drupal.org/project/acquia_purge
✩ Drupal’s PHP requirements https://www.drupal.org/docs/7/system-
requirements/php

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