This presentation has been prepared by Oleksii Prohonnyi for internal PHP team meeting for improving skills of developers.

1. DATABASE
OPTIMIZATION
_by Oleksii Prohonnyi

2. The degree of normality
in a database
is inversely proportional to that
of its DBA.

4. WHEN DO WE OPTIMIZE
THE DATABASE?

6. You should get your home page
down to 1.5 seconds.
(Google’s threshold for being
considered a “fast” website)
Best Practices for Speeding Up Your Web Site by Yahoo

7. PROFILE FIRST,
OPTIMIZE LAST

9. The basic rule of optimization is to
never assume - always verify,
using actual data.

10. PEAR_Benchmark
Stores microtime() values before and after
the query for later observation, and the
difference would be the timing of the query
with good accuracy.
Package Information: Benchmark by The PHP Group

11. PEAR_Benchmark
Example 1: Automatic profiling start, stop,
and output.

13. PEAR_Benchmark
Example 2: Manual profiling start, stop,
and output.

15. Zend_Db_Profiler
Built-in support for profiling in Zend
Framework.

17. CWebLogRoute
Built-in support for profiling in Yii
Framework.

21. It's very important to profile using
a relevant dataset.
You should create a test machine that
resembles your live dataset as much as
possible to get relevant data.

22. Another important note is to avoid
looking at cached results.
- SQL_NO_CACHE
- MySQL Caches
- OS Caches
- Hardware Caches
Query Profiling with MySQL: Bypassing caches by Peter Zaitsev

23. The Slow Query Log
Profiles queries that are used by daemons
and cron jobs and log the results to a file.
5.2.5. The Slow Query Log by Oracle Corporation

24. OPTIMIZING
PERFORMANCE

26. There are 4 basic ways to optimize
query performance:
- Rewrite the queries
- Change indexing strategy
- Change schema
- Use an external cache

27. EXAMINING QUERY
EXECUTION PLANS

28. EXPLAIN
Add the reserved word 'EXPLAIN' at the
beginning of your query to get the execution
plan for the query.
8.2.2. EXPLAIN Output Format by Oracle Corporation

31. EXPLAIN limitations:
- EXPLAIN can be wrong
- EXPLAIN works for SELECT only
- EXPLAIN may take long time
- Estimated number of rows may be very
inaccurate
….
MySQL EXPLAIN limits and errors by Peter Zaitsev

32. COMMON
OPTIMIZATIONS

34. 1. Looping queries
One of the most common mistakes is to
query in a loop without need.
Most likely looped SELECT queries can be
rewritten as a JOIN.

36. 2. Picking only needed columns
Picking only the needed columns is a good
general practice to use, and avoids those
problems.

38. 3. Filtering rows correctly and
using indexes
Our main goal is to select the smallest
amount of rows we need and doing so in
the fastest way possible.

39. Filtering rows correctly and
using indexes
Example - fetching users created in the
last 4 weeks.

41. Filtering rows correctly and
using indexes
Example - select the lowest priced fruit from
several fruit types.

43. 4. Indexing correctly
Using more indexes than is necessary can
have adverse affects - as it slows down
the operation of INSERT and UPDATE
queries, while taking up more memory.
Do you always need index on WHERE column? by Vadim Tkachenko

44. 5. Picking the right engine
for your data
MySQL has a pluggable engine design,
which allows you to use different engine
types to store your data, each with its own
advantages and drawbacks.
Chapter 14. Storage Engines by Oracle Corporation

46. CACHING

47. There are many caching strategies.
Common options include caching to disk
(files) or caching to memory (using solutions
such as memcache or APC).
Another form of caching is to the database –
by de-normalizing the schema to store data
that is the result of expensive to run queries.

48. S4I8GMA UKRAINE

49. Oleksii Prohonnyi
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