Databases Reference
In-Depth Information
P
RECISION
SERVICE
LEVELS
When you have a simple data service interface that's used across multiple applications,
you can focus on things like creating precise service levels for data services. A service
level doesn't change the
API
; it only puts precise specifications on how quickly or reli-
ably the service will perform under various load conditions. For example, for any data
service you might specify
The maximum read time to return a value
The maximum write time to store a new key-value pair
How many reads per second the service must support
How many writes per second the service must support
How many duplicate copies of the data should be created for enhanced
reliability
Whether the data should be duplicated across multiple geographic regions if
some data centers experience failures
Whether to use transaction guarantees for consistency of data or whether even-
tual consistency is adequate
One of the best ways to visualize how developers control this is to think of a series of
knobs and controls similar to what you'd see on a radio tuner, as shown in figure 4.3.
Each input knob can be adjusted to tune the service level that your business needs.
Note that as the knobs are adjusted, the estimated monthly cost of providing this data
service will change. It can be difficult to precisely estimate the total cost, since the
actual cost of running the service is driven by market conditions and other factors,
such as the cost for moving data into and out of the service.
You can configure your system to use a simple input form for setting up and allo-
cating resources to new data services. By changing the information using the form,
you can quickly change the number of resources allocated to the service. This simple
interface allows you to set up new data services and reconfigure data services quickly
without the additional overhead of operations staff. Because service levels can be
tuned to an application requirement, you can rapidly allocate the appropriate reliabil-
ity and performance resources to the system.
Inputs
Output
Max read
time
Max write
time
Reads per
second
Writes per
second
Duplicate
copies
Multiple
datacenters
Transaction
guarantees
Estimated
price/month
$435.50
Figure 4.3
NoSQL data services can be adjusted like the tuning knobs on a radio. Each knob can
individually be adjusted to control how many resources are used to provide service guarantees. The
more resources you use, the higher the cost will be.
