The document details challenges and best practices in PHP and database management, emphasizing the importance of efficient database queries and indexing. It highlights common mistakes developers make, particularly around reliance on code assumptions, and the impact of improper query handling on system performance. The author shares lessons learned from real-world projects, stressing the need for proactive analysis and optimization to avoid performance issues.

1. Beyond PHP :
It's not (just) about the code
Wim Godden
Cu.be Solutions

2. Who am I ?
Wim Godden (@wimgtr)
Founder of Cu.be Solutions (http://cu.be)
Open Source developer since 1997
Developer of OpenX
Zend Certified Engineer
Zend Framework Certified Engineer
MySQL Certified Developer
Speaker at PHP and Open Source conferences

3. Cu.be Solutions ?
Open source consultancy
PHP-centered
High-speed redundant network (BGP, OSPF, VRRP)
High scalability development
Nginx + extensions
MySQL Cluster
Projects :
mostly IT & Telecom companies
lots of public-facing apps/sites

4. Who are you ?
Developers ?
Anyone setup a MySQL master-slave ?
Anyone setup a site/app on separate web and database server ?
→ How much traffic between them ?

5. The topic
Things we take for granted
Famous last words : "It should work just fine"
Works fine today
→ might fail tomorrow
Most common mistakes
PHP code ↔ PHP ecosystem
How-to & How-NOT-to

6. It starts with...
… code !
First up : database

7. Database queries – complexity
SELECT DISTINCT n.nid, n.uid, n.title, n.type, e.event_start, e.event_start AS
event_start_orig, e.event_end, e.event_end AS event_end_orig, e.timezone,
e.has_time, e.has_end_date, tz.offset AS offset, tz.offset_dst AS offset_dst,
tz.dst_region, tz.is_dst, e.event_start - INTERVAL IF(tz.is_dst, tz.offset_dst,
tz.offset) HOUR_SECOND AS event_start_utc, e.event_end - INTERVAL
IF(tz.is_dst, tz.offset_dst, tz.offset) HOUR_SECOND AS event_end_utc,
e.event_start - INTERVAL IF(tz.is_dst, tz.offset_dst, tz.offset) HOUR_SECOND +
INTERVAL 0 SECOND AS event_start_user, e.event_end - INTERVAL IF(tz.is_dst,
tz.offset_dst, tz.offset) HOUR_SECOND + INTERVAL 0 SECOND AS
event_end_user, e.event_start - INTERVAL IF(tz.is_dst, tz.offset_dst, tz.offset)
HOUR_SECOND + INTERVAL 0 SECOND AS event_start_site, e.event_end -
INTERVAL IF(tz.is_dst, tz.offset_dst, tz.offset) HOUR_SECOND + INTERVAL 0
SECOND AS event_end_site, tz.name as timezone_name FROM node n INNER
JOIN event e ON n.nid = e.nid INNER JOIN event_timezones tz ON tz.timezone =
e.timezone INNER JOIN node_access na ON na.nid = n.nid LEFT JOIN
domain_access da ON n.nid = da.nid LEFT JOIN node i18n ON n.tnid > 0 AND
n.tnid = i18n.tnid AND i18n.language = 'en' WHERE (na.grant_view >= 1 AND
((na.gid = 0 AND na.realm = 'all'))) AND ((da.realm = "domain_id" AND da.gid = 4)
OR (da.realm = "domain_site" AND da.gid = 0)) AND (n.language ='en' OR
n.language ='' OR n.language IS NULL OR n.language = 'is' AND i18n.nid IS NULL)
AND ( n.status = 1 AND ((e.event_start >= '2010-01-31 00:00:00' AND
e.event_start <= '2010-03-01 23:59:59') OR (e.event_end >= '2010-01-31 00:00:00'
AND e.event_end <= '2010-03-01 23:59:59') OR (e.event_start <= '2010-01-31
00:00:00' AND e.event_end >= '2010-03-01 23:59:59')) ) GROUP BY n.nid HAVING
(event_start >= '2010-02-01 00:00:00' AND event_start <= '2010-02-28 23:59:59')
OR (event_end >= '2010-02-01 00:00:00' AND event_end <= '2010-02-28 23:59:59')
OR (event_start <= '2010-02-01 00:00:00' AND event_end >= '2010-02-28
23:59:59') ORDER BY event_start ASC;

8. Database - indexing
'select id from stock where status = 2 order by qty'
→ aggregate index on (status, qty)
'select id from stock where status > 2 order by qty'
→ aggregate index on (status, qty) ?
→ No : range selection stops use of aggregate index
→ separate index on status and qty

9. Database - indexing
Indexes make database faster
→ Let's index everything !
→ DON'T :
Insert/update/delete → Index modification
Each query → evaluation of all indexes
"Relational schema design is based on data
but index design is based on queries"
(Bill Karwin, Percona)

10. Databases – detecting problematic queries
Slow query log
→ SET GLOBAL slow_query_log = ON;
Queries not using indexes
→ In my.cnf/my.ini : 'log_queries_not_using_indexes'
General query log
→ SET GLOBAL general_log = ON;
→ Turn it off quickly !
Percona Toolkit (Maatkit)
pt-query-digest

11. Databases - pt-query-digest
# Profile
# Rank Query ID Response time Calls R/Call Apdx V/M Item
# ==== ================== ================ ===== ======= ==== ===== ==========
# 1 0x543FB322AE4330FF 16526.2542 62.0% 1208 13.6806 1.00 0.00 SELECT output_option
# 2 0xE78FEA32E3AA3221 0.8312 10.3% 6412 0.0001 1.00 0.00 SELECT poller_output poller_item
# 3 0x211901BF2E1C351E 0.6811 8.4% 6416 0.0001 1.00 0.00 SELECT poller_time
# 4 0xA766EE8F7AB39063 0.2805 3.5% 149 0.0019 1.00 0.00 SELECT wp_terms wp_term_taxonomy wp_term_relationships
# 5 0xA3EEB63EFBA42E9B 0.1999 2.5% 51 0.0039 1.00 0.00 SELECT UNION wp_pp_daily_summary wp_pp_hourly_summary
# 6 0x94350EA2AB8AAC34 0.1956 2.4% 89 0.0022 1.00 0.01 UPDATE wp_options
# MISC 0xMISC 0.8137 10.0% 3853 0.0002 NS 0.0 <147 ITEMS>

12. Databases - pt-query-digest
# Query 2: 0.26 QPS, 0.00x concurrency, ID 0x92F3B1B361FB0E5B at byte 14081299
# This item is included in the report because it matches --limit.
# Scores: Apdex = 1.00 [1.0], V/M = 0.00
# Query_time sparkline: | _^ |
# Time range: 2011-12-28 18:42:47 to 19:03:10
# Attribute pct total min max avg 95% stddev median
# ============ === ======= ======= ======= ======= ======= ======= =======
# Count 1 312
# Exec time 50 4s 5ms 25ms 13ms 20ms 4ms 12ms
# Lock time 3 32ms 43us 163us 103us 131us 19us 98us
# Rows sent 59 62.41k 203 231 204.82 202.40 3.99 202.40
# Rows examine 13 73.63k 238 296 241.67 246.02 10.15 234.30
# Rows affecte 0 0 0 0 0 0 0 0
# Rows read 59 62.41k 203 231 204.82 202.40 3.99 202.40
# Bytes sent 53 24.85M 46.52k 84.36k 81.56k 83.83k 7.31k 79.83k
# Merge passes 0 0 0 0 0 0 0 0
# Tmp tables 0 0 0 0 0 0 0 0
# Tmp disk tbl 0 0 0 0 0 0 0 0
# Tmp tbl size 0 0 0 0 0 0 0 0
# Query size 0 21.63k 71 71 71 71 0 71
# InnoDB:
# IO r bytes 0 0 0 0 0 0 0 0
# IO r ops 0 0 0 0 0 0 0 0
# IO r wait 0 0 0 0 0 0 0 0
# pages distin 40 11.77k 34 44 38.62 38.53 1.87 38.53
# queue wait 0 0 0 0 0 0 0 0
# rec lock wai 0 0 0 0 0 0 0 0
# Boolean:
# Full scan 100% yes, 0% no
# String:
# Databases wp_blog_one (264/84%), wp_blog_tw… (36/11%)... 1 more
# Hosts
# InnoDB trxID 86B40B (1/0%), 86B430 (1/0%), 86B44A (1/0%)... 309 more
# Last errno 0
# Users wp_blog_one (264/84%), wp_blog_two (36/11%)... 1 more
# Query_time distribution
# 1us
# 10us
# 100us
# 1ms
# 10ms ################################################################
# 100ms
# 1s
# 10s+
# Tables
# SHOW TABLE STATUS FROM `wp_blog_one ` LIKE 'wp_options'G
# SHOW CREATE TABLE `wp_blog_one `.`wp_options`G
# EXPLAIN /*!50100 PARTITIONS*/
SELECT option_name, option_value FROM wp_options WHERE autoload = 'yes'G

13. Databases – pt-query-digest – Digest UI

14. Databases – next step : explain
explain <query>
"How will MySQL execute the query"

15. Databases – next step : explain
+----+-------------+-----------+------+---------------+------+---------+------+--------+-------------+
| id | select_type | TABLE | TYPE | possible_keys | KEY | key_len | REF | ROWS | Extra |
+----+-------------+-----------+------+---------------+------+---------+------+--------+-------------+
| 1 | SIMPLE | employees | ALL | NULL | NULL | NULL | NULL | 299809 | USING WHERE |
+----+-------------+-----------+------+---------------+------+---------+------+--------+-------------+
+----+-------------+------------+-------+-------------------------------+---------+---------+-------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+-------+-------------------------------+---------+---------+-------+------+-------+
| 1 | SIMPLE | itdevice | const | PRIMARY,fk_device_devicetype1 | PRIMARY | 4 | const | 1 | |
| 1 | SIMPLE | devicetype | const | PRIMARY | PRIMARY | 4 | const | 1 | |
+----+-------------+------------+-------+-------------------------------+---------+---------+-------+------+-------+

16. Databases – next step : explain
explain <query>
"How will MySQL execute the query"
Shows :
Indexes available
Indexes used (do you see one ?)
Number of rows scanned
Type of lookup
'system', 'const' and 'ref' = good
'ALL' = bad
Extra info
Using index = good
Using filesort = usually bad
Using where = bad

17. Databases – when to use / not to use
Good at :
Fetching data
Storing data
Searching through data
Bad at :
select `someField` from `bigTable` where crc32(`field`) = "something"
→ full table scan

18. For / foreach
$customers = CustomerQuery::create()
->filterByState('SC')
->find();
foreach ($customers as $customer) {
$contacts = ContactsQuery::create()
->filterByCustomerid($customer->getId())
->find();
foreach ($contacts as $contact) {
doSomestuffWith($contact);
}
}

19. Joins
$contacts = mysql_query("
select
contacts.*
from
customer
join contact
on contact.customerid = customer.id
where
state = 'SC'
");
while ($contact = mysql_fetch_array($contacts)) {
doSomeStuffWith($contact);
}
or the ORM equivalent

20. Better...
10001 → 1 query
Sadly : people still produce code with query loops
Usually :
Growth not anticipated
Internal app → Public app

21. The origins of this talk
Customers :
Projects we built
Projects we didn't build, but got pulled into
Fixes
Changes
Infrastructure migration
15 years of 'how to cause mayhem with a few lines of code'

22. Client X
Jobs search site
Monitor job views :
Daily hits
Weekly hits
Monthly hits
Which user saw which job

23. Client X
Originally : when user viewed job details
Now : when job is in search result
Search for 'php' → 50 jobs = 50 jobs to be updated
→ 50 updates for shown_today
→ 50 updates for shown_week
→ 50 updates for shown_month
→ 50 inserts for shown_user

24. Client X : the code
foreach ($jobs as $job) { $db->query("
$db->query(" insert into shown_month(
insert into shown_today( jobId,
jobId, number
number ) values(
) values( " . $job['id'] . ",
" . $job['id'] . ", 1
1 )
) on duplicate key
on duplicate key update
update number = number + 1
number = number + 1 ");
"); $db->query("
$db->query(" insert into shown_user(
insert into shown_week( jobId,
jobId, userId,
number when
) values( ) values (
" . $job['id'] . ", " . $job['id'] . ",
1 " . $user['id'] . ",
) now()
on duplicate key )
update ");
number = number + 1 }
");

25. Client X : the graph

26. Client X : the numbers
600-1000 updates/sec (peaks up to 1600)
400-1000 updates/sec (peaks up to 2600)
16 core machine

27. Client X : panic !
Mail : "MySQL slave is more than 5 minutes behind master"
We set it up → who did they blame ?
Wait a second !

28. Client X : what's causing those peaks ?

29. Client X : possible cause ?
Code changes ?
→ According to developers : none
Action : turn on general log, analyze with pt-query-digest
→ 50+-fold increase in queries
→ Developers : 'Oops we did make a change'
After 3 days : 2,5 days behind
Every hour : 50 min extra lag

30. Client X : But why is the slave lagging ?
File : File :
master-bin-xxxx.log Slave I/O thread master-bin-xxxx.log
p Sl
um av
g d ad th e S
re Q
n lo e ad L
Bi thr
Master Slave

31. Client X : Master

32. Client X : Slave

33. Client X : fix ?
foreach ($jobs as $job) { $db->query("
$db->query(" insert into shown_month(
insert into shown_today( jobId,
jobId, number
number ) values(
) values( " . $job['id'] . ",
" . $job['id'] . ", 1
1 )
) on duplicate key
on duplicate key update
update number = number + 1
number = number + 1 ");
"); $db->query("
$db->query(" insert into shown_user(
insert into shown_week( jobId,
jobId, userId,
number when
) values( ) values (
" . $job['id'] . ", " . $job['id'] . ",
1 " . $user['id'] . ",
) now()
on duplicate key )
update ");
number = number + 1 }
");

34. Client X : the code change
$todayQuery = "
insert into shown_today(
jobId,
number
) values ";
foreach ($jobs as $job) {
$todayQuery .= "(" . $job['id'] . ", 1),";
}
$todayQuery = substr($todayQuery, -1);
$todayQuery .= "
)
on duplicate key
update
number = number + 1
";
$db->query($todayQuery);
Result : insert into shown_today values (5, 1), (8, 1), (12, 1), (18, 1), ...
Careful : max_allowed_packet !

35. Client X : the chosen solution
$db->autocommit(false); $db->query("
foreach ($jobs as $job) { insert into shown_month(
$db->query(" jobId,
insert into shown_today( number
jobId, ) values(
number " . $job['id'] . ",
) values( 1
" . $job['id'] . ", )
1 on duplicate key
) update
on duplicate key number = number + 1
update ");
number = number + 1 $db->query("
"); insert into shown_user(
$db->query(" jobId,
insert into shown_week( userId,
jobId, when
number ) values (
) values( " . $job['id'] . ",
" . $job['id'] . ", " . $user['id'] . ",
1 now()
) )
on duplicate key ");
update }
number = number + 1 $db->commit();
");

36. Client X : conclusion
For loops are bad (we already knew that)
Add master/slave and it gets much worse
Use transactions : it will provide huge performance increase
Result : slave caught up 5 days later

37. Database → Network
Customer Y
Top 10 site in Belgium
Growing rapidly
At peak traffic :
Unexplicable latency on database
Load on webservers : minimal
Load on database servers : acceptable

38. Client Y : the network

39. Client Y : the network
60GB 700GB 700GB

40. Client Y : network overload
Cause : Drupal hooks → retrieving data that was not needed
Only load data you actually need
Don't know at the start ? → Use lazy loading
Caching :
Same story
Memcached/Redis are fast
But : data still needs to cross the network

41. Network trouble : more than just traffic
Customer Z
150.000 visits/day
News ticker :
XML feed from other site (owned by same customer)
Cached for 15 min

42. Customer Z – fetching the feed
if (filectime(APP_DIR . '/tmp/ScrambledSiteName.xml') < time() - 900) {
unlink(APP_DIR . '/tmp/ScrambledSiteName.xml');
file_put_contents(
APP_DIR . '/tmp/ScrambledSiteName.xml',
file_get_contents('http://www.scrambledsitename.be/xml/feed.xml')
);
}
$xmlfeed = ParseXmlFeed(APP_DIR . '/tmp/ScrambledSiteName.xml');
What's wrong with this code ?

43. Customer Z – no feed without the source
Feed source

44. Customer Z – no feed without the source
Feed source

45. Customer Z : timeout
default_socket_timeout : 60 sec by default
Each visitor : 60 sec wait time
People keep hitting refresh → more load
More active connections → more load
Apache hits maximum connections → entire site down

46. Customer Z : timeout fix
$context = stream_context_create(
array(
'http' => array(
'timeout' => 5
)
)
);
if (filectime(APP_DIR . '/tmp/ScrambledSiteName.xml') < time() - 900) {
unlink(APP_DIR . '/tmp/ScrambledSiteName.xml');
file_put_contents(
APP_DIR . '/tmp/ScrambledSiteName.xml',
file_get_contents('http://www.scrambledsitename.be/xml/feed.xml', false, $context)
);
}
$xmlfeed = ParseXmlFeed(APP_DIR . '/tmp/ScrambledSiteName.xml');

47. Customer Z : don't delete from cache
$context = stream_context_create(
array(
'http' => array(
'timeout' => 5
)
)
);
if (filectime(APP_DIR . '/tmp/ScrambledSiteName.xml') < time() - 900) {
unlink(APP_DIR . '/tmp/ScrambledSiteName.xml');
file_put_contents(
APP_DIR . '/tmp/ScrambledSiteName.xml',
file_get_contents('http://www.scrambledsitename.be/xml/feed.xml', false, $context)
);
}
$xmlfeed = ParseXmlFeed(APP_DIR . '/tmp/ScrambledSiteName.xml');

48. Network resources
Use timeouts for all :
fopen
curl
SOAP
…
Data source trusted ?
→ setup a webservice
→ let them push updates when their feed changes
→ less load on data source
→ no timeout issues
Add logging → early detection

49. Logging
Logging = good
Logging in PHP using fopen
→ bad idea : locking issues
→ Use file_put_contents($filename, $data, FILE_APPEND)
For Firefox : FirePHP (add-on for Firebug)
Debug logging = bad on production
Watch your logs !
Don't log on slow disks → I/O bottlenecks

50. File system : I/O bottlenecks
Causes :
Excessive writes (database updates, logfiles, swapping, …)
Excessive reads (non-indexed database queries, swapping, small file
system cache, …)
How to detect ?
top
iostat
See iowait ? Stop worrying about php, fix the I/O problem !

51. File system
Worst of all : NFS
PHP files → lstat calls
Templates → same
Sessions
→ locking issues
→ corrupt data
→ store sessions in database, Memcached, Redis, ...

52. Much more than code
XML feed
Network
User
Webserver DB
server

53. Questions ?

54. Questions ?

55. Contact
Twitter @wimgtr
Web http://techblog.wimgodden.be
Slides http://www.slideshare.net/wimg
E-mail wim.godden@cu.be
Please...
Rate my talk : http://spkr8.com/t/21141

56. Thanks !
Please...
Rate my talk : http://spkr8.com/t/21141