Localizing the Work
After an SQL statement is optimized, the Dispatcher sends the individual steps that make up that query, one at a time, to some number of AMPs in the system. Steps are usually dispatched, and processes started, on all AMPs in the system. Under some conditions, the Optimizer might decide that this query work can be accomplished by accessing only a single AMP in the configuration. This is referred to as a single-AMP operation, or a single‑AMP step.
Teradata Database uses single-AMP steps to localize work to the fewest resources necessary when it is beneficial to do so. This is frequently the case for tactical queries. Single-AMP work frees the other AMPs in the system to do other work, thereby increasing the potential for overall system throughput. This is diagrammed in the following figure:
Tactical queries are most efficient and most scalable when designed around single‑ or few-AMP operations. This is the single most important way to increase throughput and preserve response times for very short tactical queries. This is diagrammed in the following figure:
Single‑ or few-AMP queries scale well because they engage the same small level of database resources even when the system doubles or triples in size (see “Effect of Configuration Expansion on Tactical Query Response Times” on page 895).