Configuring BigMemory Hybrid

To configure BigMemory Hybrid, include the following elements in the tc-config.xml file:

dataStorage - Specifies the maximum amount of data you plan to store on the server, using either DRAM alone or both DRAM and SSD flash memory.

offheap - Specifies the maximum amount of data to hold in DRAM.

hybrid - Enables the Hybrid option to use SSD flash memory in addition to off-heap DRAM.

The minimum <offheap> required for non-hybrid deployments, distributed caching and other applications is 4GB to be configured for each server.

The minimum <offheap> required for webMethods clustering in hybrid mode is 2GB. In case there are any custom caches created on the same Terracotta Server Array, then 4GB becomes the minimum requirement.

If the hybrid element is present, then the BigMemory Hybrid functionality is enabled. With Hybrid enabled, the value of the size attribute for the dataStorage element can exceed that of the size attribute for the offheap element. This enables SSD devices to supplement the DRAM and be many times larger than the DRAM.

If the hybrid element is absent, then BigMemory Hybrid functionality is off. With Hybrid off, the value of the size attribute for the dataStorage element must be less than or equal to the value of the size attribute for the offheap element. In this case, the offheap element is not required.

If the dataStorage element is absent, dataStorage size and offheap size default to 512 MB.

Although the dataStorage element is optional, if included, this element must have a value assigned to its size attribute.

Note: If you are migrating from BigMemory Max 4.0 to 4.1, the dataStorage element has replaced the maxDataSize element. The old element is still compatible for pure DRAM operation, but to enable Hybrid mode, you must use the new 4.1-compatible dataStorage element with the hybrid tag.

BigMemory Hybrid requires a unique and explicitly specified path. The default path is the Terracotta server's home directory. You can customize the path using the <data> element in the server's tc-config.xml configuration file.

If Fast Restartabillity is enabled, then if you have a restart, data will be loaded into BigMemory Hybrid in the same way as for BigMemory, with no difference in behavior or time required to get the system running again. See Fast Restartability.

If Fast Restartabillity is not enabled, then on restart, you will have some artifacts from the previous run left on disk, and you may want to remove them. For more information, see Clearing Data from a Terracotta Server.