accumulo-ohc

Accumulo-OHC is a custom cache implementation for Accumulo that builds on Caffeine and OHC. Caffeine is used for caching frequently accessed blocks on the Java heap. OHC is used for caching less frequently accessed blocks in a larger off Java heap cache. The reason to do this to avoid the Java garbage collector. This cache has been test with 1 billion key values all stored in a 4GB on-heap + 40GB off-heap cache.

Accumulo-OHC builds uses a new caching SPI introduced in Accumulo 2.0.0-SNAPSHOT.

Below is an example of how to build this project and place the needed jars in Accumulo's lib/ext directory. This would need to be done on each tablet server.

mvn clean package dependency:copy-dependencies
cp target/*.jar target/dependency/*.jar $ACCUMULO_HOME/lib/ext

Below is example of configuring this cache in the Accumulo shell. After doing this, would need to restart tablet servers.

config -s tserver.cache.manager.class=accumulo.ohc.OhcCacheManager
config -s tserver.cache.config.ohc.default.logInterval=30
config -s tserver.cache.config.ohc.data.on-heap.maximumWeight=1000000000
config -s tserver.cache.config.ohc.data.off-heap.capacity=10000000000
config -s tserver.cache.config.ohc.index.on-heap.maximumWeight=100000000
config -s tserver.cache.config.ohc.index.off-heap.capacity=1000000000
config -s tserver.cache.config.ohc.summary.on-heap.maximumWeight=100000000
config -s tserver.cache.config.ohc.summary.off-heap.capacity=10000000000

An alternative to configuring this cache in the shell is setting properties in accumulo.properties. Below is an example of that.

tserver.cache.manager.class=accumulo.ohc.OhcCacheManager
tserver.cache.config.ohc.default.logInterval=30
tserver.cache.config.ohc.data.on-heap.maximumWeight=1000000000
tserver.cache.config.ohc.data.off-heap.capacity=10000000000
tserver.cache.config.ohc.index.on-heap.maximumWeight=100000000
tserver.cache.config.ohc.index.off-heap.capacity=1000000000
tserver.cache.config.ohc.summary.on-heap.maximumWeight=100000000
tserver.cache.config.ohc.summary.off-heap.capacity=10000000000

This cache uses a pass through strategy for configuration, properties are passed through to Caffeine and OHC. Properties are of the form

tserver.cache.config.ohc.[default|data|index|summary].[off-heap|on-heap].<pass through prop>

The options default|data|index|summary determines the Accumulo cache instance. The options off-heap|on-heap determines if the pass through prop goes to Caffeine or OHC.

For example, the following property

tserver.cache.config.ohc.data.on-heap.maximumWeight=1000000000

will pass maximumWeight=1000000000 to Caffeine for the Accumulo data cache.

As another example,the following property

tserver.cache.config.ohc.data.off-heap.capacity=10000000000

will pass capacity=10000000000 to OHC.

For documentation on what properties each cache implementation accepts see OHCCacheBuilder and CaffeineSpec.

Additionally a property can be set to periodcally log stats for each cache. The value for this is seconds. By default no logging is done. The property is of the form :

tserver.cache.config.ohc.[default|data|index|summary].logInterval=<seconds>