Database Reference
In-Depth Information
Control Module
The control module maintains the configuration information about:
The configurations of the load balancer, including proxy address and proxy script.
The configurations of the monitor module, such as heartbeat interval and monitor
interval.
The access information of each virtualized database replica server, namely host
address, port number, user name, and password.
The location information of each virtualized database replica server, such as
us-
east
,
us-west
,
eu-west
.
And in addition to the application-defined SLA, the tolerated replication delay of
each virtualized database replica server for this study.
In practice, the SLA of the replication delay for each virtualized database replica
server,
delay
sla
, is defined as an integer value in the unit of millisecond which
represents two main components:
delay
sla
D
delay
rtt
C
delay
tolerance
(7.3)
where the round-trip time component of the SLA replication delay,
delay
rtt
,isthe
average round-trip time from the virtualized database master server to the virtualized
database replica server. In particular, it represents the minimum delay cost for
replicating data from the master to the associated slave. The tolerance component of
the replication delay,
delay
tolerance
, is defined by a constant value which represents
the tolerance limit of the period of the time for the replica server to be inconsistent.
This tolerance component can vary from one replica server to another depending on
many factors such as the application requirements, the geographic location of the
replica server, and the workload characteristics and the load balancing strategy of
each application.
One of the main responsibilities of the control module is to trigger the action
module for adding a new virtualized database replica server, when necessary, in
order to avoid any violation in the application-defined SLA of data freshness for the
active replicas. In framework implementation, an intuitive strategy is followed to
trigger the action module for adding a new replica server when it detects a number
of continuous up-to-date monitored replication delays of a replica server which
exceeds its application-defined threshold, T , of SLA violation of data freshness.
In other words, for a running replica server, if the latest T monitored replication
delays are violating its SLA of data freshness, the control module will trigger the
action module to activate the geographically closest replica server according to
the location of the violating replica server. It is worthy to note that the strategy
of the control module in making the decisions regarding the addition a new replica
server in order to avoid any violence of the application-defined SLA can play an
important role in determining the overall performance of the framework. However,
