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From Hakan Baba <ahakanb...@gmail.com>
Subject What does readRequestCount metric include in addition to get and scanNext operations?
Date Thu, 04 Jul 2019 19:41:28 GMT
In hbase region and regionserver metrics I cannot understand the
relationships between metrics related to read requests, get and scanNext
operations.

The hbase.regionserver.readRequestCount is documented here
<https://hbase.apache.org/book.html#rs_metrics> as:

hbase.regionserver.readRequestCount

The number of read requests received

In addition to that, there are also get_num_ops and scanNext_num_ops metrics.
I cannot find an official documentation for them. They are mentioned in
this ticket <https://issues.apache.org/jira/browse/HBASE-15376>.

In the metrics I see, the readRequests are orders of magnitude larger than
the sum of all get and scanNext requests in one regionserver. For
example:[image:
ReadGetScanMetrics] <https://i.stack.imgur.com/3fyGk.png>

Please note that the y-axis is in log scale.

The plots are using these Wavefront queries

ReadRequestRate

sum(rate(ts(hbase.regionserver.server.readRequestCount,
source="*<sourceSelector>*" )))

GetNumRate

sum(rate(ts(hbase.regionserver.regions.get_num_ops,
source="*<sourceSelector>*")))

ScanNumRate

sum(rate(ts(hbase.regionserver.regions.scanNext_num_ops,
source="*<sourceSelector>*" )))

What may be the reason of that huge delta ? What does readRequest counter
include in addition to get and scanNext operations ?

Some unproven theories of mine.

   1. Maybe the readRequests counter increments for each row read during a
   scanNext call ?
   2. Maybe the readRequest counter increments with async replication jobs,
   region replication, cross datacenter replication etc.

Note this is running HBase 1.2.0-cdh5.11.0


You can see this question also in server fault, if you like to see a
different formatting.

https://serverfault.com/q/973638/428655

Thanks

Hakan

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