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Open Source Database Clusters?
grugruto asks: "A lot of open source solutions are available to scale web sites with clusters but what about databases? I can't afford an Oracle RAC license but can I have something more reliable and fault tolerant than my single Postgres box? I have seen this recent article that looks promising for open source solutions. Do anyone have experiences with clusters of MySQL , Postgres-R, C-JDBC or other solutions? How does it compare to commercial products?"
For what it's worth, the commercial solutions are hard to setup, unstable and terribly difficult to maintain, and this is after a small fortune has been invested in making them work. Not to knock the open source solution, but it's hard to beleive that something that is infrequently used and difficult to understand will be truly production quality if you want to use it for money.
MySQL has very nice replication functionality, and, in certain circumstances, you can even set up replication rings. It is somewhat flexible about the topology you choose to use, so pick the one best for your application. Load balance ala DNS and you're in business.
Do anyone have experiences with clusters of MySQL , Postgres-R, C-JDBC or other solutions? How does it compare to commercial products?
They don't compare to commercial products. I know it isn't what you want to hear, and there are hundreds of kids here to tell you different, but they just dont compare. Those kids database experience doesn't extend past an address book.
Even if you manage to get them to technically keep up, transaction wise, to Oracle or SQL Server, the ACID enforcement isn't there, the syntaxes are kludgy. Gack.
My company ships products with SQL Server or Oracle as the back end. I've tried to put together an OSS solution so I could impress the big boss with millions of bucks of saved license fees. They just aren't anywhere close IMO.
Run a SQL Server farm on the back end if you cant afford an Oracle license. Don't be an OSS idealogue in the business world, you end up unemployed.
I don't need no instructions to know how to rock!!!!
HA is always crapshoot/tradeoff between cost and risk. Throw enough $ at the problem and you'll approach 100% availability.
I know that 'more robust' is a nice thing to want, but you really need to think about what you really need. If it takes 15 minutes to switch over to a backup copy (using some magic RAID disk mirroring maybe?) and 15 minutes to restart the app and let it checkpoint it's way up to a decent operational speed again, is that good enough?
If it takes an hour, how about that?
How much time/heartache or money is it worth for you to have system downtime, and how much are you willing to expend to reduce it by 5, 15, 30 minutes?
So, there's really a continuum of availabilty you have to pick your point in. At the low end, you have no backups and recreate everything from scratch. At the high end you use Vendor X's real clustering solution and 24x7 monitoring, then have zero downtime even in a disaster. Somewhere in the middle is you.
Now I realise this an overtly commercial view of things, but if needs be replace money with effort and season to taste.
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Two options I haven't seen anyone mention yet are PostgreSQL eRServer 1.0+ (see PostgreSQL news item "PostgreSQL now has working, tested, scalable replication!" from August 28, 2003 or a lengthier press posting "PostgreSQL, Inc. Releases Open Source Replication Version") and Backplane.
eRServer has been in development for over two years, is used in production settings and is released under a BSD license (as with PostgreSQL). It uses a single master/multiple slave asynchronous replication scheme. There are cautions in the release that replication may be difficult to setup.
Backplane seems to be particularly well-suited to clustering data quickly across a WAN. A quote may explain it better:
I haven't used either yet, but you may wish to give them a look.