Don't have every handler update regionserver metrics on each
scan#nextRaw; instead, do a batch update just before Scan
returns. Otherwise, all running handlers end up contending
on metrics update.
M hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java
Update of regionserver metrics counters moved out to caller where
can be done as a batch update instead of per-next.
M hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsRegionServer.java
Class doc to encourage batch updating metrics.
Remove the single update as unused anymore.
M hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java
Count calls to nextRaw. Update regionserver count in finally block when
scan is done rather than per nextRaw call. Move all metrics updates to
finally.
Signed-off-by: Reid Chan <reidchan@apache.org>
Signed-off-by: Baiqiang Zhao <ZhaoBQ>
3331e8307a