See Metrics for an introduction and how to enable Metrics emission.
Block cache item count in memory. This is the number of blocks of storefiles (HFiles) in the cache.
Block cache hit ratio (0 to 100). TODO: describe impact to ratio where read requests that have cacheBlocks=false
Block cache size in memory (bytes). i.e., memory in use by the BlockCache
Size of the compaction queue. This is the number of stores in the region that have been targeted for compaction.
Filesystem read latency (ms). This is the average time to read from HDFS.
Total number of read and write requests. Requests correspond to RegionServer RPC calls, thus a single Get will result in 1 request, but a Scan with caching set to 1000 will result in 1 request for each 'next' call (i.e., not each row). A bulk-load request will constitute 1 request per HFile.
Sum of all the storefile index sizes in this RegionServer (MB)
Number of stores open on the RegionServer. A store corresponds to a column family. For example, if a table (which contains the column family) has 3 regions on a RegionServer, there will be 3 stores open for that column family.