Effect of Configuration Expansion on Tactical Query Response Times
For a complex query, adding nodes translates to a proportional decrease in response time because the work is distributed across a larger number of AMPs. At the same time, the response time for a query that accesses a single AMP, as many tactical queries do, is not affected by the number of AMPs in the configuration.
There is a one benefit gained by single‑AMP tactical queries when nodes are added to a configuration: more of them can be performed at the same time and still deliver short turnaround times.
Consider the following contrived example: Assume you have a table with a cardinality of 1 million rows. The read capacity of each node in your configuration is 100 rows per second. If you are doing a complex strategic query that involves a full table scan of this table, then the response time for the query diminishes proportionally with the increase in nodes, as illustrated by the data in the following table:
|
Number of Nodes |
Number of Rows per Node |
Response Time (seconds) |
|
1 |
1,000,000 |
10,000 |
|
10 |
100,000 |
1,000 |
|
100 |
10,000 |
100 |
|
200 |
5,000 |
50 |
This performance enhancement occurs because each node has fewer rows as more nodes are added, so each node can perform its portion of the scan faster.
On the other hand, if your application is performing single‑ or few-AMP tactical queries, adding nodes does not shorten the response time. However, it does increase the number of tactical queries that can be performed in a given interval of time, as indicated by the data in the following table:
|
Number of Nodes |
Response Time (seconds) |
Throughput (requests/second) |
|
1 |
0.01
|
100 |
|
10 |
1,000 |
|
|
100 |
10,000 |
|
|
200 |
20,000 |