suppose a Sybase 12.5.3 failover setup on Sun Solaris 9, with a shared disk for the user database. The primary companion has direct access to the user database, the secondary has access through a proxy database.
When users on the secondary companion issue queries on the user database, these will eventually be taken (by way of CIS) to the primary database.
Will the primary companion carry all the load for the user connections on the secondary companion?
Will the secondary's transaction log contain correct entries for all transactions (that are actually physically executed on the primary companion)?
What of the workload on the proxy database remains for the secondary companion? Will it sit - more or less - idly, just redirecting queries to the primary by way of CIS?
I normally do not recommend my cleints use proxy database. This puts un-necessary network load and people are led to believe that on the outset they are getting load - balancing(which is absurd). Ultimately all the load is on the destination server, irrespective of which serevr that you login from. Honestly, I don't understand why Sybase markets this feature?
The downside of Proxy is, once setup there is no backing out unless you redo the whole companionship again. We struggled for a while, and figured out an unsupported mechansim to knock of entries from sysalternates to get rid off proxy.
So the secondary companion will sit more or less idly with its proxy db, directing all work to the destination server. But what other solution would there be, without the proxy db? A failover solution with two servers having different databases is worth nothing. Why should I want to failove to such a server if it didn't serve the same database?
The proxy db solution is not the best one can imagine - especially as it prevents any load balancing - but still the only usable one.
I wished Sybase would direct its HA efforts more in the direction of a shared cache or so - like Oracle's RAC. The problem with Failover is that nothing is shared (during operations).
The way it was envisaged during initial HA inception was to share proxy databases on both primary and companion. This sort of gives load balancing as far as databases are concerned. This still isn't true load balancing.
Sybase has not deleivered any major feature enhancements to HA since 12.5, except maybe just new certifications on platforms. I beleive all the resources are now devoted towards delivering Sybase Clusters, which is a true cluster environment, apparently much superior to Oracle RAC in functionality.
Last edited by willy_and_the_ci; 02-25-06 at 22:46.
That would be interesting! I'm looking forward to it :-)
I know Oracle's RAC as well and think that it's got a nice concept, but it also has problems of its own - e.g. what concerns scalability, or integration with other HA services. Much development going on, this is also not finished...
A look from a different angle, and a revised product from Sybase would certainly benefit users of database clustering technology in general.