Yingchun Lai has posted comments on this change. ( 
http://gerrit.cloudera.org:8080/14128 )

Change subject: [metrics] Add a metric to count merged entities when merge 
metrics
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Patch Set 4:

(4 comments)

http://gerrit.cloudera.org:8080/#/c/14128/3//COMMIT_MSG
Commit Message:

PS3:
> In discussing this, are you sure we want to introduce the concept of a "sub
I agree, I will do these changes.


http://gerrit.cloudera.org:8080/#/c/14128/3//COMMIT_MSG@13
PS3, Line 13: check whether a table is balanced or not by thirdparty monitor 
system.
> I saw this in my first pass but forgot to comment: how is this an effective
When we use rebalancer to check per-table balance status of a cluster, we have 
to fetch balance info table by table (by add --tables=xx flag), and also we 
have to "run command" in monitor system and this tool seems not fast enough 
because it will call function like RetrieveAllTablets.
When table level metrics "merged_entities_count" are included in metrics from 
tserver, different tserver may have different values of this metric for a 
table, we can check it and jugde whether it's balance or not.


http://gerrit.cloudera.org:8080/#/c/14128/3/src/kudu/tablet/tablet.cc
File src/kudu/tablet/tablet.cc:

http://gerrit.cloudera.org:8080/#/c/14128/3/src/kudu/tablet/tablet.cc@163
PS3, Line 163: METRIC_DEFINE_gauge_size(tablet, merged_entities_count,
> Would it be possible to prevent the count from being displayed when regular
I've added a function "InvalidateEpoch()" to class Metric, which will set 
"m_epoch_" to -1. So if a metric is initialized and InvalidateEpoch()ed, but 
never changed, it's invisible.


http://gerrit.cloudera.org:8080/#/c/14128/2/src/kudu/util/metrics.cc
File src/kudu/util/metrics.cc:

http://gerrit.cloudera.org:8080/#/c/14128/2/src/kudu/util/metrics.cc@479
PS2, Line 479:   // metrics, we should keep them around until the next poll.
> Is tablet->table the only kind of merge allowed? Or is it possible to merge
It's not the only kind, we may perform more merge types.
Done



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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I652b457a2df73414f95f5d1d5efaa003cc262bd1
Gerrit-Change-Number: 14128
Gerrit-PatchSet: 4
Gerrit-Owner: Yingchun Lai <[email protected]>
Gerrit-Reviewer: Adar Dembo <[email protected]>
Gerrit-Reviewer: Kudu Jenkins (120)
Gerrit-Reviewer: Yingchun Lai <[email protected]>
Gerrit-Comment-Date: Tue, 03 Sep 2019 16:09:24 +0000
Gerrit-HasComments: Yes

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