From: Tom Sawyer <transami@...>
Date: 2003-01-26T13:18:59+09:00
Subject: Re: mod_ruby: what's persistent and what's shared?

On Saturday 25 January 2003 08:12 pm, ahoward wrote:
> have you had any issues sharing one connection between many processes?  i
> mean what if :
> 1)  process a :
>     $db.exec 'connect foobar_database'
> 2)  process b :
>     $db.exec 'connect barfoo_database'
> 3) process a :
>     $db.exec # something which has something to do with foobar_database,
> but # it's connected to barfoo_database!!

i get around this by storing the connections in a hash based on connection 
info. so connections to different dbs/users get their own connection in the 
pool.

here's the code:

module DBI

  # singleton instance
  # provides simple pooling of database connections
  # note: the pools are defined by dsn and username;
  # thus optional parameters are expected to be the same for these

  def DBI.instance(dsn, user, pass, *args)
    @@dbi = {} unless defined?(@@dbi)
    @@dbi["#{dsn}::#{user}"] ||= DBI.connect(dsn, user, pass, *args)
    return @@dbi["#{dsn}::#{user}"]
  end

end

> > it runs as a seperate service (using DRb)?
>
> yes.  it's a totall hack right now, but the _idea_ is a good one i think.
> making it totally generic would be tough, but the general idea would be to
> place a naming service in a rinda space or simply a drb object which you
> could look up other objects by.  the rinda space would allow you to leave
> object behind between cgi invocations (with all the problems that entails).
>  what i'm really looking into now is how to efficiently multiplex and bunch
> of database connections, eg how to design a connection pool.  anyone out
> there done this?

very cool. sorry i don't really have any expertise in this to help. the above 
DBI.instance is my extent. let me know how it goes though.

> > i wonder then. if i use DRb would i then also be able to make my app
> > easily run on a distributed enviornment? i.e. a cluster?
>
> yeah.  that's a definitely possibility and one which i've considered.

see. now that would be the best reason to use it, i think.

-- 
tom sawyer, aka transami
transami@transami.net