Configuring the maximum capacity of a data grid

You can define a maximum capacity for each data grid in a collective. Configuring a maximum capacity limits the amount of data storage that a particular data grid can use. The capacity limit ensures that the available storage capacity for the collective is used in a predictable manner.

Before you begin

About this task

After you configure maximum capacity limits on each data grid in the collective, the capacity limit is enforced by comparing the total size of all primary data in the data grid to the configured capacity limit for the data grid. The capacity used by replica copies of data is not counted when the data grid is measured against the configured capacity limit.

The maximum capacity limit is a maximum amount of data that can be inserted into the data grid. The limit is not a guarantee of an allocated amount of space for the data grid. Therefore, a data grid might not be able to reach its configured capacity limit if the collective does not have the capacity to store the data. Reasons for insufficient capacity in the collective might be a high capacity limit on the data grid, or capacity that is consumed by other data grids in the collective.

When the capacity limit for a particular data grid is breached, the grid handles insert operations in one of the following ways:
  • By default, insert operations that would breach the grid limit capacity are rejected. Client processes receive an exception in response to insert requests. Read, update, and delete operations succeed even if the data grid is exceeding its capacity limit. With these limited operations, the data grid can run at a minimum level of function but additional growth of the data grid is prevented.
  • Available only on a simple data grid, you can override this default behavior by selecting the Use least recently used (LRU) eviction for this data grid option. Selecting this option accommodates new inserts into a simple data grid and maintains the capacity limit by removing the least recently used data entry. Setting the maximum capacity on a data grid does not require a restart, however if you have selected the LRU option on a simple grid, then the grid will automatically be restarted for changes to take affect. This is also the case if you decide to turn off the LRU option on a simple grid.

Procedure

  1. In the user interface, click Data Grid > data_grid_type > data_grid_name > Show advanced attributes.
  2. Select Limit the amount of capacity for this data grid.
  3. If you are setting the maximum capacity for a simple data grid and want the grid to accept new insert operations (instead of rejecting them) at the expense of least recently used data entries, then select Use least recently used (LRU) eviction for this data grid. Click Apply Changes to save. You are warned that the data in the grid will be lost in order to complete the restart.
  4. View the current capacity consumption to determine the maximum capacity to define for the selected data grid. You can also ensure that you are not exceeding the total capacity of the collective.
    The bar chart shows data consumption of MyGrid, all limited grids, and all unlimited grids. The capacity limit of MyGrid, all limited data grids, and the total collective capacity are charted with vertical lines.
    In this chart, the current data grid that is being configured, MyGrid, is currently using 900 megabytes of capacity. It has a currently configured capacity limit of 2000 megabytes. At the collective level, the total capacity of the collective is 4000 megabytes. In addition, the total of all the configured limits on the capacity-limited data grids is 3400 megabytes. Those grids are currently using 2900 megabytes. Finally, there is at least one data grid in the collective that does not have a capacity limit defined. These data grids without defined capacity limits are consuming approximately 900 megabytes.
  5. Enter a value for the limit of primary data consumption in MB. When you press enter, the potential maximum capacity consumption of the primary and replica data displays. This number varies based on the number of replicas that you have defined. However, remember that the number of replicas is limited by the number of appliances in the collective. If you have four replicas defined, and three appliances in the collective, your collective contains one primary and two replicas.
  6. Click Apply changes to save the configuration. You do not need to restart your data grid to activate the new limit.

Example

Capacity limit example: Multiple data grids

Data grids A, B, and C are defined in a collective with a total capacity of 600 gigabytes of storage. No replicas are defined on any of the data grids. Data grid A has a capacity limit of 100 gigabytes. Data grid B has a capacity limit of 50 gigabytes. Data grid C has a capacity limit of 200 gigabytes. In this scenario, at least 250 gigabytes of unused capacity are always available in the collective. The total size of the three data grids cannot grow beyond 350 gigabytes.

Capacity limit example: Replicas

Data grid A is defined in a collective of two appliances. Data grid A has one synchronous and two asynchronous replicas, for a total of three replicas. The grid capacity limit is defined as 100 megabytes. Initially the maximum capacity consumption of this grid is 200 megabytes. Because the collective has only two appliances, one primary and one replica copy of the data exist. The primary data grid can use up to 100 megabytes. The replica grows at the same rate as the primary data grid, resulting in a maximum total consumed capacity of 200 megabytes. If a third appliance is added to the collective, a second replica copy of the data is placed. The maximum consumption of the grid becomes 300 megabytes, from the one primary plus two replicas.

Capacity limit example: Data grids with no capacity limit

Data grids A, B, and C are defined in a collective with a total capacity of 600 gigabytes of storage. Data grid A has a limit of 100 gigabytes. Data grid B has a limit of 50 gigabytes. Data grid C has no capacity limit. No replicas are defined for any of the three grids. Because data grid C has no limit, the data grid could potentially consume the entire 600 gigabytes of available capacity. As a result, data grid A and data grid B would not be able to insert any data. Any data that data grid A or data grid B inserted remains, but the data grids are not guaranteed to be able reach their capacity limits. Data grid C is guaranteed to have at least 450 gigabytes available to consume because the only other data grids on the system cannot consume more than a total of 150 gigabytes out of the 600 gigabytes of capacity. This 450 gigabyte calculation ignores any capacity that is consumed by the replica data. If two or more unlimited data grids exist in the collective, the potential capacity of any specific data grid is not guaranteed.
Parent topic: Configuring data grids