SMP (symmetric multiprocessing) is the processing of programs by multiple processors that share a common operating system andmemory. In symmetric (or "tightly coupled") multiprocessing, the processors share memory and the I/O bus or data path. A single copy of the operating system is in charge of all the processors. SMP, also known as a "shared everything" system, does not usually exceed 16 processors.
SMP systems are considered better than MPP systems for online transaction processing (OTP) in which many users access the same database in a relatively simple set of transactions. An advantage of SMP for this purpose is the ability to dynamically balance the workload among computers (and as a result serve more users faster).
An SMP gives consistent performance because all processors have equal access to disk resources, and when communication between processes in the DBMS are required, it is accomplished at memory speeds which are two orders of magnitude faster than MPP message-based interconnects. With the consequences of disk layout being so minor compared to database partitioning on an MPP, the choice of SMP architectures is one that brings consistency in performance, as well as scalability.
A skeptical database administrator, however, will not accept these qualitative arguments without real performance data to back them up, and fortunately the TPC-D benchmarks provide a means for all vendors to put forth their best performance measurements.
Mohib Alvi 