From: Eric Hodel <drbrain@...7.net>
Date: 2003-01-31T14:04:13+09:00
Subject: Re: drb experts


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ahoward (ahoward@fsl.noaa.gov) wrote:

> On Fri, 31 Jan 2003, Eric Hodel wrote:
>=20
> > Here I meant client and server processes.
>=20
> me too.
>=20
> 'well, the client and server will be the same in my case'.gsub
>   /will be the same/, 'will be on the same host/'
>=20
>=20
> > Anything you write to should have a mutex around it, unless you don't c=
are
> > about lost updates.
>=20
> you mean anthing outside the local scope of the method called?
>=20
> eg. @var, @@var, $var, etc.
>=20
> > Let me clear this up with a little code:
> [code very helpfull - thanks!!!]
>=20
> > When you use Undumped, DRb passes a proxy of the object across to
> > the client, so everything done through the object takes place on
> > the server side, not the client side.  The client only needs to load
> > DRb.
>=20
> ahhh.  i wondered if this were the case.  can anyone explain the 'un' in
> UnDumped?  'un' becaues it is not actually dumped, but proxies are return=
ed
> instead?

If you watch the transactions with tcpdump, you can see the actual
object coming across without undumped.  Normally, DRb use Marshall and
dump to send the object across.

> > If you don't use Undumped, you need to load all the libraries used by t=
he
> > class on the client side.
>=20
> in my case - the cgi process would need postgres.so, etc.
>=20
> > For a DB driver, this would be the postgres drives, and you'd get the w=
hole
> > driver on each Apache process.  The more Apache processes you have, the=
 more
> > overhead this takes up.
>=20
> as i mention above, the client and server side would be the same in my ca=
se,
> since the cgi (client) would be using a pool (server) running on my web/db
> server machine(s).  i wonder though, if in this case the cost would actua=
lly
> be that high as you think since postgres.so would be shared for all proce=
sses
> - surely 'require' does a shared mapping and not a private one?
>=20
> in fact, it seems like in the case of using the client and server on the =
same
> machine - at least where *.so's are concerned - there would be little
> differnce in overhead since the one image would be in memory regardless. =
 have
> you done any performance tests of this situation?

Well, if they are separate Apache processes, then it would fall to your
OS's ld.so to do a shared mapping (which I'm sure is smart).  The
overhead would be for anything you'd do in ruby before it hits the DB,
the code for querying, quoting, etc.

I would expect that DRb would be slower, because each Apache process can
have its own DB connection, and one process won't block the others
during I/O.  DRb adds the overhead of marshalling and dumping objects
across a TCP/IP socket.

How much slower that will be though, I don't know.

--=20
Eric Hodel - drbrain@segment7.net - http://segment7.net
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