CloudDB AutoAdmin - Large Scale and Big Data: Processing and Management - page 363

In general, there exists many forms of SLAs with different metrics. In this chap-
ter, we focus on the following two main consumer-centric SLA metrics:

• Data freshness , which represents the tolerated window of data staleness for

each database replica. In other words, it represents the time between a com-
mitted update operation on the master database and the time when the opera-
tion is propagated and committed to the database replica (Section 11.6).

• Transaction response time , which represents the time between a transac-

tion is presented to the database system and the time when the transaction
execution is completed (Section 11.7).

Figure 11.2 shows an overview of our framework architecture, which consists
of three main modules: the monitor module, the control module , and the action
module. In this architecture, the consumer application is only responsible for con-
figuring the control module of the framework by declaratively defining (using an
XML dialect) the specifications of the SLA metrics of their application. In addition,
the consumer application declaratively defines (using another XML dialect) a set of
rules that specify the actions that should be taken (when a set of conditions are satis-
fied) to meet the expected system performance or to reduce the cost of the allocated
cloud resources when they are not efficiently utilized. More details and examples
about the declarative definitions of the application-specific SLA metrics and action
rules will be presented in Sections 11.6 and 11.7. The control module also maintains
the information about the configurations of the load balancer (e.g., proxy address,
proxy script), the access information of each database replica (e.g., host address, port
number), and the location information of each database replica (e.g., us-east, us-west,

Define

Replication delay monitor

Monitor
module

Response time monitor

Application

...

Database
proxy

Configurations

Slave 1

Replication delay control

Control
module

Slave ...

Response time control

...

Slave k

Master

Load balancer actions

Action
module

Database actions

...

FIGURE 11.2 Framework architecture.