Queuing Time or Qt – Queuing Time is defined as the time spent waiting in a queue for access to computing resources. Queuing Time for a given business transaction can be also be defined as the End to End Queuing Time for access of any of the following physical resources i.e.
- Queuing Time for access to Disk Resource
- Queuing Time for access to CPU Resources
- Queuing Time for access to Application Server Resources
- Queuing Time for access to Database Server Resources
Let’s revisit our basic equation for Response Time:
- Rt = Wt + St ……………………. [ Wt = Wait Time, St = Service Time ] also written as
- Rt = Qt + St ……………………. [ Wt = Wait Time, Qt = Queuing Time ]
Queuing Time [ Wt or Qt ] for a given application business transaction doesn’t remain constant and is a variable that can change based on the congestion within the system and movement of congestion points within the given system. Longer queuing times will translate into more dropped connections and surely a lot more irate customers.
The Queue length for a given system or resource within a system can be calculated using the below formula:
- Q = X * Qt ……………………….. [ X = Throughput, Qt = Queuing Time ]
Performance Testing is generally conducted to identify potential system bottlenecks and understand the extent of queuing the system can take before the overall system performance starts degrading. Queuing on a system is inevitable and one can only invest that much of money to eliminate queuing based on choice of application designs and deployment architectures.
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