Guidelines for configuring On-Heap BlockCache (LruBlockCache)

You need to determine the proportions of READ and WRITE operations in your workload, and use these proportions to specify on-heap memory allocation for BlockCache and MemStore.

The sum of the on-heap memory allocations for BlockCache and MemStore properties must be less than or equal to 0.8. The following table describes these two properties:


Property	Default Value	Description
`hfile.block.cache.size`	0.4	Proportion of maximum JVM heap size (Java `-Xmx` setting) to allocate to BlockCache. A value of 0.4 allocates 40% of the maximum heap size.
`hbase.regionserver.global.memstore.upperLimit`	0.4	Proportion of maximum JVM heap size (Java `-Xmx` setting) to allocate to MemStore. A value of 0.4 allocates 40% of the maximum heap size.

Use the following guidelines to determine the two proportions:

The default configuration for each property is 0.4, which configures BlockCache for a mixed workload with roughly equal proportions of random reads and writes.
If the amount of avaiable RAM in the off-heap cache is less than 20 GB, your workload is probably read-heavy. In this case, do not plan to configure off-heap cache, your amount of available RAM is less than 20 GB. In this case, increase the hfile.block.cache.size property and decrease the hbase.regionserver.global.memstore.upperLimit property so that the values reflect your workload proportions. These adjustments optimize read performance.
If your workload is write-heavy, decrease the hfile.block.cache.size property and increase the hbase.regionserver.global.memstore.upperLimit property proportionally.
As noted earlier, the sum of hfile.block.cache.size and hbase.regionserver.global.memstore.upperLimit must be less than or equal to 0.8 (80%) of the maximum Java heap size specified by HBASE_HEAPSIZE (-Xmx).

If you allocate more than 0.8 across both caches, the HBase RegionServer process returns an error and does not start.
Do not set hfile.block.cache.size to zero.

At a minimum, specify a proportion that allocates enough space for HFile index blocks. To review index block sizes, use the RegionServer Web GUI for each server.

Edit the corresponding values in your hbase-site.xml files.

Here are the default definitions:

<property>
     <name>hfile.block.cache.size</name>
     <value>0.4</value>
     <description>Percentage of maximum heap (-Xmx setting) to allocate to block
       cache used by HFile/StoreFile. Default of 0.4 allocates 40%.
     </description>
 </property>
 
 <property>
     <name>hbase.regionserver.global.memstore.upperLimit</name>
     <value>0.4</value>
     <description>Maximum size of all memstores in a region server before new
       updates are blocked and flushes are forced. Defaults to 40% of heap.
     </description>
 </property>

If you have less than 20 GB of RAM for use by HBase, you are done with the configuration process. You should restart (or perform a rolling restart on) your cluster and check log files for error messages. If you have more than 20 GB of RAM for use by HBase, consider configuring the variables and properties described next.