A data grid is a storage
unit that can be
created to hold objects for a specific application or set of applications.
A collective groups appliances together for scalability
and management purposes. A zone defines a physical location
for your appliance and are used to determine the placement of the
data in your cache.
Appliance
topology
Both collectives and zones
are associated with one or more
WebSphere® DataPower® XC10 Appliances. Each appliance
can be a member of one collective and one zone. Each appliance hosts
multiple data grids, which hold the cache data.
Figure 1. Collectives
and zones topology
Important: Two appliances are required to make your
data grid highly available.
Data grids
Data grids hold the objects for
your applications. By caching objects, you can increase the performance
of your application. There are three types of
data grids:
- Simple data grid
- Simple data grids hold
data in key-value pairs. For example, you can store the results of
a database query in a simple data grid.
You use the ObjectMap API to implement a simple data grid. The ObjectMap API works
similarly to Java Maps.
- Session data grid
- If you are using WebSphere Application
Server sessions,
you can configure your application to use a session data grid on the appliance for
session management data. You can configure your application to use
a session data grid when you
are installing a new application. You can also update your existing
application or server settings to use the session data grid on the appliance.
- Dynamic cache data grid
- You can use
a dynamic cache data grid on
the appliance to store
data from your WebSphere Application
Server dynamic
cache. You can enable applications that are written with the Dynamic
Cache API or applications that use container-level caching, such as
servlets, to use the appliance as the cache provider. As a result,
less memory is used by your application servers. All the cache data
is offloaded to the appliance and is no longer stored in application
server memory.
Data grid
replicas
You can define the number
of replicas that are available for a given data grid. Replicas are created
when you have at least two appliances in your collective. If you have
one appliance, no replicas are created.
Replicas can be synchronous
replicas or asynchronous replicas. Synchronous replicas receive updates
as part of the transaction on the primary data grid. Asynchronous replicas
are updated after the transaction on the primary data grid is committed. Synchronous
replicas guarantee data consistency, but can increase the response
time of a request when compared with an asynchronous replica. Asynchronous
replicas do not have the same guarantee in data consistency, but can
make your transactions complete faster. A data grid has one asynchronous
replica by default. A placement algorithm controls where the replicas
are located.
Collectives
When
you define a collective, the
following information is shared among the appliances in the collective:
data grids, monitoring information,
collective and zone members, and users with the other appliances in
the collective. When you update any of this information, your changes
are persisted to all of the other appliances in the collective. The
catalog
service enables the communication between appliances. The catalog
service is a group of catalog servers. Each appliance in the collective
runs a catalog server, with a limit of three catalog servers for each
collective. If you have more than three appliances in a collective,
the catalog service runs on the first three appliances that were added
to the collective. If you remove an appliance with a catalog server
from the collective or an appliance with a catalog server becomes
unavailable, the next appliance that you add to the collective runs
a catalog server. The catalog server does not fail over to other appliances.
To
add an appliance to a collective, add the host name and secret key
for the appliance to the collective configuration panel in another
appliance. You can create this configuration from any appliance in
the collective, because the collective membership is persisted among
the collective members.
Appliances can only be in one collective.
You cannot add an appliance that is already in a collective to a different
collective. You also cannot join collectives. To join appliances from
separate collectives, you must remove each appliance from its respective
collective, making each appliance stand alone. You can then create
a new collective that includes all of the appliances.
While
you can use a collective to make most configuration changes, you must
log in to a given appliance to change the settings on the and panels.
Zones
Zones are associated with a physical
location of the appliance, such as a city or rack location in a lab.
Zones help the catalog service to define where the data in your data grids is stored. For example,
if the primary information for your data grid is stored in a given
zone, then the replica data is stored in an appliance that is in a
different zone. With this configuration, failover can occur from the
primary to a replica if the appliance that holds the data grid primary fails.