Distributed Systems Techniques

Distributed systems techniques are key to building transparency into clusters. By structuring applications and systems as modules that interact by using remote procedure calls, applications become more modular and can be distributed among nodes of the cluster. The client calls upon a service by name. The procedure call either invokes the service locally or uses a remote procedure call if the service is remote.

Microsoft has invested heavily in structuring its software as components that interact by using remote procedure calls. The resulting infrastructure goes by the following names:

OLE—object linking and embedding
COM—component object model
DCOM—distributed COM

Many aspects of the COM are in place today. In particular, with Windows NT Server 4.0 and Microsoft SQL Server 6.5, Microsoft delivered:

DCOM—distributed creation of objects in a network based on remote procedure calls.
OLE Transactions (also called Microsoft Distributed Transaction Coordinator)—distributed transactions that allow applications to do work at many Microsoft SQL Server database partitions and automatically (transparently) get the ACID distributed transaction semantics (atomicity, consistency, isolation, and durability).

Windows NT Server supports these features along with many other cluster facilities including cluster security (domains), cluster software management (SMS), cluster naming (distributed name service), and cluster performance monitor (Perfmon). Microsoft SQL Server complements these facilities with management tools built into SQL Enterprise Manager that allow it to manage and monitor an array of Microsoft SQL Servers.