Drupal can be a resource-intensive system. Any moderately complicated site will generate a lot of database queries and use a fair amount of memory to build pages to serve to visitors. With some judicious tuning, however, Drupal can perform really well, and at scale. In this webinar, Drew Webber, Principal Support Engineer at Acquia, will discuss some common pitfalls encountered by sites that struggle in the face of increased traffic. Attendees will walk away with a deeper understanding of: -The most common problems encountered when it comes to Drupal site performance -Ways of identifying performance bottlenecks on your Drupal site -How to avoid these common pitfalls and remedy these issues (often without writing a single line of code!) -What not to do when building and running your site

1. Common Drupal Pitfalls
...and how to avoid them.
Acquia Webinar, 18-May-2015

2. Common Drupal Pitfalls
● Key performance and scalability issues
○ How to identify them
● What not to do

3. Acquia Insight

4. Cache
● Drupal's page cache
● Keep it anonymous
○ avoid SESSions
● External caching
● Purging and long TTLs
● Block / Views / Panels / Authcache
● Drupal 8

5. HTTP headers
$ curl -SLIXGET http://example.com/node/123
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
X-Drupal-Cache: HIT
Content-Language: en
X-Generator: Drupal 7 (http://drupal.org)
Cache-Control: public, max-age=600
Expires: Sun, 19 Nov 1978 05:00:00 GMT
Vary: Cookie,Accept-Encoding
Last-Modified: Mon, 31 Mar 2016 11:12:16 GMT
Date: Tue, 01 Apr 2016 08:17:03 GMT
X-Varnish: 1396807672 1396807385
Age: 77
Via: 1.1 varnish
Connection: keep-alive
X-Cache: HIT
$ curl -SLIXGET http://example.com/node/123
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
X-Drupal-Cache: MISS
Content-Language: en
X-Generator: Drupal 7 (http://drupal.org)
Cache-Control: no-cache, must-revalidate, post-check=0, pre-check=0
Expires: Sun, 19 Nov 1978 05:00:00 GMT
Vary: Cookie,Accept-Encoding
Set-Cookie: SESS7e45dac0b46e8ea9=yvUDWgHqHYMHnflx6EZOaFu5c; expires=Thu,
24-Apr-2016 11:49:45 GMT; path=/; domain=.example.com; HttpOnly
Last-Modified: Tue, 01 Apr 2016 08:16:25 GMT
Date: Tue, 01 Apr 2016 08:16:27 GMT
X-Varnish: 1396807518
Age: 0
Via: 1.1 varnish
Connection: keep-alive
X-Cache: MISS
✔ !!?!

6. Database
● Typically single-threaded
● ...is a slow cache backend
○ e.g. memcache
○ cache_form
● Avoid writes wherever possible
○ dblog, statistics
● Slow query logging

7. Slow query digest (percona)
# Query 2: 0.00 QPS, 0.15x concurrency, ID 0x2FA97A9508A98849 at byte 1909177
# This item is included in the report because it matches --limit.
# Attribute pct total min max avg 95% stddev median
# ========= ====== ======= ======= ======= ======= ======= ======= =======
# Count 0 18
# Exec time 18 3337s 1s 652s 185s 314s 145s 167s
# Lock time 0 56ms 0 56ms 3ms 0 13ms 0
# Rows sent 0 0 0 0 0 0 0 0
# Rows exam 1 1.34M 1003 97.67k 76.19k 97.04k 39.91k 97.04k
# Tables
# SHOW TABLE STATUS FROM `slowsite` LIKE 'node'G
# SHOW CREATE TABLE `slowsite`.`node`G
# EXPLAIN /*!50100 PARTITIONS*/
SELECT DATE_FORMAT((DATE_ADD('19700101', INTERVAL node.created SECOND) + INTERVAL -25200 SECOND), '%Y%m') AS created_year_month,
COUNT(node.nid) AS num_records, 'archive:default' AS view_name
FROM
{node} node
WHERE (( (node.status = '1') ))
GROUP BY created_year_month, view_name
ORDER BY created_year_month DESC
LIMIT 30 OFFSET 0

8. Resources
● PHP processes
○ run cron via drush
● APC / opcode cache
○ disable UI modules
● Memory / time
○ bootstrap smoke test
○ memory_profiler
○ XHProf and / or New Relic

9. bootstrap smoke test
$ drush dt-bst
operation time time-delta memory memory-delta
starting bootstrap_full 0 0 29.75MB 29.75
finished includes 13 13 33MB 3.25
loading enabled modules 13 0 33MB 0
loading module webform 26 0 34.5MB 0
loaded module webform 31 5 36MB 1.5
loading module block 31 0 36MB 0
loaded module block 32 1 36.25MB 0.25
[...snip...]
start hook_init in googleanalytics 253 0 85.5MB 0
end hook_init in googleanalytics 255 2 85.5MB 0
start hook_init in img_assist 255 0 85.5MB 0
end hook_init in img_assist 255 0 85.5MB 0
start hook_init in menu_minipanels 255 0 85.5MB 0
end hook_init in menu_minipanels 654 399 125.25MB 39.75
start hook_init in mollom 654 0 125.25MB 0
end hook_init in mollom 656 2 125.25MB 0
start hook_init in nice_menus 656 0 125.25MB 0
end hook_init in nice_menus 657 1 125.25MB 0
[...snip...]
start hook_init in views 674 0 125.25MB 0
end hook_init in views 675 1 125.25MB 0
start hook_init in rules 675 0 125.25MB 0
end hook_init in rules 675 0 125.25MB 0
finished hook_init 675 0 125.25MB 0
end of bootstrap_full 675 0 125.25MB 0

10. memory_profiler
syslog output:
Mar 13 06:30:04 slowsite: http://www.example.com|1394692204|memory profiler|123.45.67.89|http://www.example.com/index.php||0||108.75 MB - home
with some awk magic:
Path Count Max(MB) Min(MB) Avg(MB)
admin/content/node 9 59 37.25 54.03
sites/default/files/imagecache/product/abcde_123456789.jpg 3 14 14 14.00
user/[num]/addresses 3 58.25 57.25 57.83
admin/build/modules/list 9 115 66.25 73.97
user/login 32 102.5 57 59.12
wishlist 9 58.5 57.25 57.69
user/password 91 104 34.5 56.21
most-reviewed/[num] 24 66.5 61 63.23
user/[num]/order/[num] 79 106.25 35.75 60.07
search/apachesolr_search/[keywords] 3757 110.5 16.75 47.74
user/[num]/edit 48 59.5 20.25 47.61
node/[num]/edit 68 113.75 28.25 60.82
node/[num] 64024 128 25.75 65.14

11. XHProf

12. New Relic

13. Don't forget to...
● Set up Fast404
○ (partially built in since D7)
● Load test
○ practice failing
● Plan for growth / expansion
○ e.g. organisation of files directory

14. 404 handler
# Pass all requests not referring directly to files in the filesystem to
# index.php. Clean URLs are handled in drupal_environment_initialize().
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !=/favicon.ico
RewriteRule ^ index.php [L]

15. What not to do
● Blocking external call (in eval’d PHP stored in the db, to a dyndns host)
● Hacking core (badly)
● variable_set (see cache_debug)
● debugging left on / error_reporting off
● drupal_add_js() with a timestamp
● nuke cache from orbit
● expensive 404s
● PHP filter for anon
● one way ticket releases

16. Thank You - Questions?