Побочные эффекты

Небольшое введение в тему тестирования производительности, на примере тестирования PostgreSQL на скорость выполнения запросов.

A test plan is a document detailing a systematic approach to testing the performance of a system. The most obvious part of the plan defines test cases which can be expressed as simply as SQL statements.

Another part of the plan defines the environment requirements which usually consist of the hardware and software used for testing. However, this should also attempt to define potential side effects on the server side which might impact performance, such as processes running periodically or the state of the buffer cache:

# CREATE TABLE foo (id SERIAL NOT NULL PRIMARY KEY, value INTEGER NOT NULL);
# INSERT INTO foo (value) SELECT i FROM generate_series(1, 1000000) i;
# \timing
# SELECT * FROM foo WHERE value = 1;
Time: 124.278 ms
# \! sudo sync
# \! echo 3 | sudo tee -a /proc/sys/vm/drop_caches
# SELECT * FROM foo WHERE value = 1;
Time: 265.871 ms

In order to mitigate the impact of the environment on performance, the test execution part of the plan should make the necessary provisions for running multiple times. So, in the final result analysis part, it could then be possible to produce mean or median values of the performance.

остальное здесь: http://cr3bits.wordpress.com/2010/06/28/performance-testing-in-postgresql/

На примерах показано, как влияют на результаты тестирования разные побочные эффекты. Рассказано, что следует предпринять, чтобы свести их к минимуму.

original post http://vasnake.blogspot.com/2013/12/blog-post_9599.html