MOB cache properties

Opening a MOB file places the corresponding HFile-formatted data in active memory. Too many open MOB files can cause a RegionServer to exceed the memory capacity and cause performance degradation. To minimize the possibility of this issue arising on a RegionServer, you must tune the MOB file reader cache to a size that HBase can scale.

The MOB file reader cache is a least recently used (LRU) cache that keeps only the most recently used MOB files open. Refer to the MOB Cache Properties table for variables that can be tuned in the cache. MOB file reader cache configuration is specific to each RegionServer, so assess and change, if needed, each RegionServer individually. You must manually add any of the following properties you may require in the HBase Service Advanced Configuration Snippet (Safety Valve) for hbase-site.xml property.

The following properties are available for tuning the HBase MOB cache.

Property Default Description
hbase.mob.file.cache.size 1000 The opened file handlers to cache. A larger value benefits read operations by providing more file handlers per MOB file cache and reduces frequent file opening and closing. However, if the value is too high, errors such as "Too many opened file handlers" might be logged.
hbase.mob.cache.evict.period 3600 The amount of time in seconds after a file is opened before the MOB cache evicts cached files.
hbase.mob.cache.evict.remain.ratio 0.5f The ratio expressed as a float between 0.0 and 1.0, that controls how many files remain cached after an eviction is triggered due to the number of cached files exceeding the value assigned to the hbase.mob.file.cache.size property.