Prerequisites to configure Off-Heap Memory (BucketCache)

	Note
	Before configuring off-heap memory, complete the tasks in the previous "Configuring BlockCache" section.

To prepare for BucketCache configuration, compare the figure and table below before proceeding to the "Configuring BucketCache" steps.

In the following table:

The first column refers to the elements in the figure.
The second column describes each element and, if applicable, its associated variable or property name.
The third column contains values and formulas.
The fourth column computes values based on the following sample configuration parameters:
- 128 GB for the RegionServer process (there is additional memory available for other HDP processes)
- A workload of 75% reads, 25% writes
- HBASE_HEAPSIZE = 20 GB (20480 MB)

	Note
	Most of the following values are specified in megabytes; three are proportions.


Item	Description	Value or Formula	Example
A	Total physical memory for RegionServer operations: on-heap plus off-heap ("direct") memory (MB)	(hardware dependent)	131072
B	The `HBASE_HEAPSIZE` (`-Xmx`) property: Maximum size of JVM heap (MB) This value was set when the BlockCache was configured.	Recommendation: 20480	20480
C	The `-XX: MaxDirectMemorySize` option: Amount of off-heap ("direct") memory to allocate to HBase (MB)	A - B	131072 - 20480 = 110592
Dp	The `hfile.block.cache.size` property: Proportion of maximum JVM heap size (`HBASE_HEAPSIZE`, `-Xmx`) to allocate to BlockCache. The sum of this value plus the `hbase.regionserver. global.memstore.size` must not exceed 0.8. This value was set when the BlockCache was configured.	(proportion of reads) * 0.8	0.75 * 0.8 = 0.6
Dm	Maximum amount of JVM heap to allocate to BlockCache (MB)	B * Dp	20480 * 0.6 = 12288
Ep	The `hbase.regionserver. global.memstore.size` property: Proportion of maximum JVM heap size (`HBASE_HEAPSIZE`, `-Xmx`) to allocate to MemStore. The sum of this value plus `hfile.block.cache.size` must be less than or equal to 0.8.	0.8 - Dp	0.8 - 0.6 = 0.2
F	Amount of off-heap memory to reserve for other uses (DFSClient; MB)	Recommendation: 1024 to 2048	2048
G	Amount of off-heap memory to allocate to BucketCache (MB)	C - F	110592 - 2048 = 108544
	The `hbase.bucketcache.size` property: Total amount of memory to allocate to the off-heap BucketCache (MB)	G	108544