Berkeley DB Replication & Ruby on Leopard

I've been messing around with Berkeley DB & Ruby this evening as an experiment. I wanted to try out their replication support along with master election. This may wind up being a faster way of doing master election than the PAXOS library I wrote for ruby. Anyways, getting replication enabled in Ruby BDB on Leopard wasn't straightforward. The macports versions of Berkeley DB don't have threads enabled so the replication manager isn't there. So...

First build DB46 with threads

download db-4.6.21 from oracle

tar -zxf db-4.6.21.tar.gz
cd db-4.6.21/build_unix
../dist/configure --with-prefix=/usr/local --enable-cxx --disable-tcl --enable-pthread_api
make
sudo make install

Then build BDB

wget ftp://moulon.inra.fr/pub/ruby/bdb.tar.gz
tar -zxf bdb.tar.gz
cd bdb-0.6.2
ruby extconf.rb --with-db-dir=/usr/local/BerkeleyDB.4.6 --with-db-version=-4.6
make
sudo make install

You should now have a working Ruby/Berkely DB setup with replication working, hurray.

Why use parens in Ruby?

Here is another ruby gotcha. Ruby allows you to skip parenthesizing method calls. These two lines are equivelent:

set_table_name "users"
set_table_name("users")

In some cases this will make your code mildly more readable. In practice though this is dangerous. Consider this code:

if arr1.include? "foo" && !arr2.include? "bar" then
  # do something
end

Ruby order of operations says that && will be evaluated prior to calling my_array.include?. So first you evaluate:

"foo" && !arr2.include? "bar"

Which always returns true or false. Then you evaluate;

if arr1.include? true
  # do something
end

Which is clearly not what you intended. This code is correct:

if arr1.include?("foo") && !arr2.include?("bar") then
  # do something
end

As a rule, you should never call a function without parenthesizing the parameters. Even if you are writing code which is not in an IF statement or is in an IF statement, but is not a part of boolean logic, you should still parenthesize it because it is possible someone else will come along and change your code not realizing this gotcha exists. Code defensively, use parens.

Nice Ruby Reference

This site provides a references for many rdocs in one place

http://www.noobkit.com/

Covers:

ActionMailer 1.3.3
ActionPack 1.13.3
ActionWebService 1.2.3
ActiveRecord 1.15.3
ActiveSupport 1.4.2
Daemons 1.0.6
Ferret 0.11.4
Hpricot 0.6
net-ssh 1.1.2
pdf-writer 1.1.3
Rails 1.2.3
Rake 0.7.3
RedCloth 3.0.4
RFacebook 0.6.2
Rio 0.4.0
RSpec 1.0.5
Ruby 1.8.6
Syntax 1.0.0

Rails & MySQL gotcha

Hey everyone, just so you know. Don't ever do this in MySQL:

SELECT * FROM foo WHERE id IS NULL;

MySQL has a known bug that will cause this to return the last row inserted into the DB, ie. something random, instead of what you are looking for. This is fixed in MySQL version 5.0.25 which will probably be in our next upgrade. Until then:

do this:

def find_user_by_id(user_id)
  return nil if user_id == nil

  @user ||= User.find_by_id(user_id )
  @user
end

not this:

def find_user_by_id(user_id)
  @user ||= User.find_by_id(user_id )
  @user
end

For more information, see...

http://bugs.mysql.com/bug.php?id=14553

Hey guys, you may already know this but in ActionScript there is an object you can use for passing references to members functions of a class called Delegate. This is useful for associating event listeners to a method on an instance of a class rather than a static:


function hookEvent(element)
{
  element.onSelectionChange = Delegate.create(this, this.on_change);
}

function on_change() // <-- note: not a static
{
  // do stuff
}

Using this helps a lot with your code organization. This pattern is also available in javascript though it's slightly more arcane:

setTimeout((function() {this.sendPoll()}).bind(this), this.options.timeout);

-jay

Log rotation in Ruby

I just checked in a modification to the standard log object that changes a few things to allow for nice log rotation. First, log objects you create through Log.create now use a wrapper class for the webrick log object. You can still use all the methods on the logger object like .info, .debug etc. However, the log engine now keeps track of all created logfiles & when it recieves a SIGUSR1 on linux it will reopen all the log files:


jay@foo:/var/log/call_svc$ ls
call_svc-std.log.1 call_svc-std.log.2
jay@foo:/var/log/call_svc$ ps -ef | grep ruby
jay 4435 4003 0 11:59 pts/0 00:00:02 ruby bin/ragi_server.rb
jay@foo:/var/log/call_svc$ kill -SIGUSR1 4435
jay@foo:/var/log/call_svc$ ls
call_svc-std.log call_svc-std.log.1 call_svc-std.log.2


So this means we can now create logrotate scripts that don't require restarting any services:


/var/log/call_svc/call_svc-std.log {
    rotate 30
    daily
    postrotate
        /sbin/kill -SIGUSR1 `cat /snapvine/pids/call_svc`
    endscript

}


I'll try to find a moment to clean it up and post it...

-jay

Why use symbols in Ruby?

I ran a test where I did the following:
- created 100,000 random 32 character strings
- choose 1,000 of those strings randomly
- found each of the 1,000 strings in the 100,000 string array

I did this using strings, then the same exact string converted into symbols to see how the performance compares for symbol matching & string matching. Here are the results on my laptop:

Test String Time = 38.2969999313354
Test Symbol Time = 26.4219999313354

The results are independent of the ordering of the two operations and are fairly consistent. It is interesting how non-linear this is with the length of the string:

2 char/10k test set:
Test String Time = 1.84299993515015
Test Symbol Time = 1.35999989509583

8 char/10k test set:
Test String Time = 3.20300006866455
Test Symbol Time = 2.67199993133545

32 char/10k test set:
Test String Time = 3.15700006484985
Test Symbol Time = 2.73399996757507

256 char/10k test set:
Test String Time = 3.28099989891052
Test Symbol Time = 2.6560001373291

Yes, comparing 256 character strings took LESS time than comparing 32 character strings. Clearly there is some form of indexing in play here.