Oracle Essentials [Electronic resources] : Oracle Database 10g, 3rd Edition نسخه متنی

11.5 Massively Parallel Processing Systems

Clusters
historically have been limited in the throughput they can deliver by
the number of shared disk connections possible, because the disks
have to be linked physically to each system. Recent advances in
serial and fiber channel disk technology have raised disk performance
and capacity. But this increased capability has also raised issues of
management complexity, because each node introduces another discrete
copy of the operating system. With Real Application Clusters,
managing the multiple Oracle instances that make up the cluster is
essentially the same as managing a single instance, but the multiple
machines and the underlying operating systems still make for a
greater management burden.

Oracle Database 10g also introduces Automatic Storage Management (ASM), which helps to manage large amounts of disk space; see the discussion in Chapter 5.

Massively Parallel Processing (MPP)
systems appeared in the early 1990s to address these limitations.
Unlike clusters, the disks in an MPP environment are not shared
across multiple nodes, except for high-availability configurations,
so the architecture is sometimes called
"shared nothing"
(shown in Figure 11-4). A special console provides additional
operating system-management tools to make management of the many
operating system copies appear to be more transparent.

Figure 11-4. Massively Parallel Processing (MPP) configuration (four SMP nodes shown)

In a typical MPP configuration multiple nodes reside in a single
cabinet, but MPP configurations can grow to a series of cabinets with
hundreds of nodes. The nodes are linked together via a high-speed
switch and may be further linked to other cabinets of nodes via
cables that physically connect the switch to the other cabinets. The
switch provides each of the nodes with multiple interconnects to
adjacent nodes. As nodes are added additional paths are enabled
between the nodes, and the total throughput possible by the switch
continues to scale with the connections. Individual nodes can be
single processor or SMP. Oracle Real Application Clusters can use
either configuration, although SMP nodes can be utilized for
additional parallelism against data residing on a local node and are
becoming the default.

The
overall performance is a function of the power of individual nodes,
the total number of nodes, the throughput offered by the switch, and
the distribution of data. For example, in a business intelligence
query, a 64-way SMP platform could outperform an MPP platform with 16
4-way SMP nodes, because these types of queries are usually CPU-bound
and MPP interconnects are slower than an SMP memory bus. The tradeoff
is that the MPP configuration can be much larger than a single SMP
platform (although the cost of the MPP solution can be much higher
than that of an SMP system).

The most common implementation of Oracle on MPP utilizes the IBM
RS/6000 SP. Prior to including a cluster file system with Oracle
Database 10g, Oracle RAC relied on a version of IBM AIX for the SP
that included the Virtual Shared Disk (VSD). This software enabled
the disk on the SP to appear as a shared disk, even though the disk
is directly connected to an individual node. Today, the SP is much
less popular, even among IBM customers. Scalability of
IBM's 64-bit SMP nodes led to increased deployment
of small SMP clusters built from IBM's Regatta class
servers (e.g. the p690 and later) and the high-speed switch
technology created for the SP as an interconnect.