"RailsConf: Stefan Kaes - Rails Performance" by Nick

Sun, 13 Aug 2006 17:06:51 +0000

Heh, yeah, maybe it’s about time for me to get off my rear end and customize my typo so it doesn’t look like every other typo blog out there, including railsexpress.de!

"RailsConf: Stefan Kaes - Rails Performance" by Yan

Fri, 11 Aug 2006 22:33:35 +0000

bleh, my bad, I thought this was stefan’s blog :)

"RailsConf: Stefan Kaes - Rails Performance" by Yan

Fri, 11 Aug 2006 22:33:04 +0000

Hi Stefan,

any news on the template optimizer? Sounds like a really interesting and valuable idea. I am very concerned with rails performance in the views..thanks!

RailsConf: Stefan Kaes - Rails Performance

Nick Sieger — Fri, 23 Jun 2006 20:40:00 +0000

Stefan starts by citing a factor of 4-5 improvement in performance in Rails over the last year.

Performance, broken down

Latency -- how fast
Throughput -- how many
Utilization -- how idle is the cpu
Cost efficiency -- performance per unit cost

For completeness calculate the min, max, mean and standard deviation of these metrics and use the deviation as your guide for how reliable the data is.

Tools

Log files (level > Logger::DEBUG)
Rails Analyzer Tools (Eric Hodel)
Benchmarker (script/benchmarker)
DB vendor tools
Apache bench (ab or ab2)
httperf
railsbench (Stefan Kaes)

Railsbench

Railsbench measuress raw performance of rails request processing. It’s configured using config/benchmarks.yml and config/benchmarks.rb. These files let you control which requests get benchmarked, whether to create a new session when benchmarking them, etc.

Profiling Tools

Ruby Profiler
Zen Profiler
rubyprof
Rails profiler script
Ruby Performance Validator

At this point Stefan gave an overview of RPV, which appears to be a nifty tool that lets you get typical hotspot tree views of where time is spent in code. It currently only runs on Windows.

Session containers

In memory -- if you server crashes...oops. Also doesn’t scale.
File system -- easy to set up, scales with NFS, but slower than...
ActiveRecordStore -- easy to set up since it comes with Rails, but much slower than...
SQLSessionStore -- which uses the same table structure as ActiveRecordStore, but was written by Stefan to overcome performance issues with ActiveRecordStore. Setup is more involved.
memcached -- slightly faster than SQLSessionStore, scales best, but setup is also more involved.
DrbStore -- distributed ruby store

Caching

Full pages -- fastest, complete pages are served on the filesystem. Web server bypasses appserver for rendering. If you have private pages, you can’t use it.
Actions -- pages are cached after an action is rendered. The user ID can be used as part of the storage key.
Fragments -- fragments can be cached in memory, on the file system, in a DrbStore, or in memcached. Memcached scales the best but doesn’t support expiring fragments by regular expression.

ActionController

Stefan recommends avoiding components, and replacing them with helpers or partials. He has not found a use for them.

ActionView

Don’t create unnecessary instance variables in the controller; creating them in the view with instance_variable_set and accessing with instance_variable_get is slow.

Helpers

pluralize -- don’t use the inflector if you don’t need to, it’s expensive.
linkto and urlfor are among the slowest helpers, since they need to use routes. Instead, if you have page with lots of links, you might consider hard-coding the links. This reduces the amount of GC by up to 50% and the GC time down by a few percentage points (11.3% to 8.7% of total processing time).

ActiveRecord

use the :include option to prefetch associations, it avoids extra onesy-twosy SQL statements.
use piggy-backing plugin for has_one or belongs_to relationships -- allows you to retrieve extra attributes from additional tables in the same fetch query.
Field values are retrieved from the DB mostly as strings, so type conversion happens on each access, which can be slow.

Language-level and miscellaneous issues

Method calls are the slowest -- don’t needlessly create method abstractions
Short-circuit intermediate results to improve performance
Cache results in instance variables or class variables
Don’t call ObjectSpace.each_object on each request

Ruby Memory Management

designed for batch scripts, not long-running servers.
no generational garbage collection.
this is suboptimal for Rails because ASTs are stored on the heap (biggest portion of non-garbage for Rails apps), and get processed/traversed more often than they need to be
Railsbench includes a patch to allow one to recompile Ruby and tweak the garbage collector.

Rails Template Optimizer

Stefan has started a project to “compile” templates.
The idea is to cache results of some ERb scriptlets and essentially “compile” or replace the template with one that has more expressions expanded or inlined.
Code forthcoming; I assume you can stay tuned to Rails Express for news.

Questions

There was a question on JRuby -- Stefan replied that it would certainly solve GC issues, but he doesn’t know if it’s in a state to be able to benchmark Rails requests.
What are your recommendations for a web server. I don’t have any.
Is horizontal or vertical scaling better? I don’t know, I’ve been focused on making single requests go fast, so I don’t have enough experience.

Nick Sieger: RailsConf: Stefan Kaes - Rails Performance

"RailsConf: Stefan Kaes - Rails Performance" by Nick

"RailsConf: Stefan Kaes - Rails Performance" by Yan

"RailsConf: Stefan Kaes - Rails Performance" by Yan

RailsConf: Stefan Kaes - Rails Performance

Performance, broken down

Tools

Railsbench

Profiling Tools

Top Rails Performance Problems

Session containers

Caching

ActionController

ActionView

Helpers

ActiveRecord

Language-level and miscellaneous issues

Ruby Memory Management

Rails Template Optimizer

Questions