In three-tiered web applications, some form of admission control is required to ensure
that throughput and response times are not significantly harmed during periods of heavy
load. We propose Q-Cop, a prototype system for improving admission control decisions
that computes measures of load on the system based on the actual mix of queries being
executed. This measure of load is used to estimate execution times for incoming queries,
which allows Q-Cop to make control decisions with the goal of minimizing the number
of requests that are not serviced before the client, or their browser, times out.
Using TPC-W queries, we show that the response times of different types of queries
can vary significantly, in excess of 50% in our experiments, depending not just on the
number of queries being processed but on the mix of other queries that are running simultaneously.
The variation implies that admission control can benefit from taking into
account not just the number of queries being processed, but also the mix of queries. We
develop a model of expected query execution times that accounts for the mix of queries
being executed and integrate that model into a three-tiered system to make admission
control decisions. This approach makes more informed decisions about which queries
to reject, and our results show that it significantly reduces the number of unsuccessful
client requests. Our results show that this approach makes more informed decisions about
which queries to reject and as a result significantly reduces the number of unsuccessful
client requests.
For comparison, we develop several other models which represent related work in
the field, including an MPL-based approach and an approach that considers the type of
query but not the mix of queries. We show that Q-Cop does not need to re-compute
any modelling information in order to perform well, a strong advantage over most other
approaches. Across the range of workloads examined, an average of 47% fewer requests
are denied than the next best approach.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OWTU.10012/4573 |
| Date | January 2009 |
| Creators | Tozer, Sean |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
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