[kudu-CR] Add a cached boolean whether DMS is empty

["Todd Lipcon (Code Review)" <ge...@cloudera.org>]

Hello Adar Dembo,

I'd like you to do a code review.  Please visit

    http://gerrit.cloudera.org:8080/3004

to review the following change.

Change subject: Add a cached boolean whether DMS is empty
......................................................................

Add a cached boolean whether DMS is empty

On servers which store a couple TB of data, I see a good portion of a core
being burned in DeltaTracker::DeltaMemStoresEmpty(). Even the component lock
is a rw-lock, the atomic instructions necessary to acquire the lock cost a lot.

This adds a boolean member to DeltaTracker which is set on update to
try to reduce this CPU load.

Change-Id: I721ee74a112d968a33a1a82419b3268c08b67c79
---
M src/kudu/tablet/delta_tracker.cc
M src/kudu/tablet/delta_tracker.h
2 files changed, 15 insertions(+), 7 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/04/3004/1
-- 
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I721ee74a112d968a33a1a82419b3268c08b67c79
Gerrit-PatchSet: 1
Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-Owner: Todd Lipcon <to...@apache.org>
Gerrit-Reviewer: Adar Dembo <ad...@cloudera.com>