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----- Original Message -----
From: "Sean Ward" <SeanWard@xxxxxxx>
To: <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Sent: Tuesday, April 04, 2000 5:33 PM
Subject: Re: mysql through lvs?
> Actually, I ran into the same problem (ie, load balancing and scaling
mysql)
> recently. The way that I solved this is I wrote a sql dispatch daemon,
which
> can execute a sql statement concurrently on several backend systems. Then,
I
> rewrote my app so that it seperated reads from writes. Basically, what my
> program now does is track a set of open connections to mysql servers, and
> how many requests are pending on each, and when a new request comes in, it
> choses the least weighted connection, and processes all the reads along
> that. Any writes which are required (I have a high read/write ratio) are
> written to a file, which is then picked up by the dispatch daemon, and
> executed in parallel across the server. The dispatch daemon also has the
> advantages that because it records a global log of changes, I can bring a
> new server into sync my snapshotting another server's DB files, and then
> replaying the log from the time of the snapshot.
This looks like Oracle's redo logs. It's a very clever method but it has one
drawback : if reads occur in the period of time between the 'demanded' write
and the actual database update, they won't reflect the changes, particularly
if the server is highly loaded (because it will take longer to process the
logs). In Oracle, this technique is used for backup and repair purposes like
you do. Some applications dont need to immediately reflect changes and there
the method is excellent.
> If that kind of arrangement
> is of any help to you, check out lsdproject.sourceforge.net where I've
stuck
> up the source for the dispatch deamon. I'll probably have the read only
> connection balancer up there too in a few days, depending on interest. The
> problem I found with using LVS for load balancing was the need to create a
> new connection for each request (a slow operation) to get the new
connection
> load balanced. Its faster to have a pool of open connections and balance
> between them in user land.
> -Sean Ward
Thank you for providing this code !
Jc
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