Posts Tagged ‘plexed
The Tandem NonStop SQL system is composed of processor clusters interconnected via 4-plexed fiber optic rings. The systems are typically configured at a disk per MIPS, so each ten MIPS, processor has about ten disks. Disks are typically duplexed and managed in the standard way [BITT88]. Each disk pair has a set of processes managing a large RAM cache, a set of locks,and log records for the data on that disk pair. Considerable effort is spent on optimizing sequential scans by prefetching large units, and by filtering and manipulating the tuples with sql predicates at these disk servers.
Relations are range partitioned across multiple disk pairs [TAND87] which is the only strategy provided. The partitioning attribute is also used as the primary, clustering attribute on each node, making it impossible to decluster a relation by partitioning on one attribute and then constructing a clustered index at each node on a different attribute. Parallelization of operators in a query plan is achieved by inserting a parallel operator (which is similar to Volcano’s exchange operator [GRAE90]) between operator nodes in the query tree and joins are executed using nested or son-merge algorithms. Scans, aggregates, updates, and deletes are parallelized. In addition several utilities use parallelism (e.g. load, reorg, …). A hash join algorithm which uses hash declustering of intermediate and final results has recently been implemented [ZELL90]. [ENGL89] contains a performance evaluation of the speedup and scaleup characteristics of the parallel version of the Non-Stop SQL system.
The system is primary designed for transaction processing. The main parallelism feature for OLTP is parallel index update. Relational tables typically have five indices on them, although it is not uncommon to see ten indices on a table. These indices speed reads, but slow down inserts, updates, and deletes. By doing the index maintenance in parallel, index maintenance time can be held constant if the indices are spread among many processors and disks. In addition, the NonStop SQL is fault tolerant and suppons geographically distributed data and execution.