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From Todd Lipcon <t...@cloudera.com>
Subject Re: counters and scanners inconsistency
Date Tue, 17 Jan 2012 02:21:23 GMT
Hi Young,

This is interesting and unexpected behavior. What version are you running?

If you can write a unit test (or system test) that demonstrates the
problem against a running cluster, that would be excellent.


On Fri, Jan 13, 2012 at 4:59 PM, Young <youngmaeng@gmail.com> wrote:
> I'm having an odd problem with incrementing counters simultaneously during a scan (both
in separate processes).
> For low rate counters, there is no problem (< 1 increment per second), but for the
higher rate counters (>10 increments per second), there is an inconsistency in the counter
> Averaging the values over time gives the correct count (i.e. the counter itself is still
increasing correctly), but at certain samples the counter drops down to some seemingly random
number.  This random number is consistent for about a day and a half then jumps to a different
random number for the next day and a half - this cycle coincides exactly with compaction of
the table in question.
> Again, the counter value itself, when it is not equal to the random number of the day,
is correct.  I'm wondering if there is something going on underneath that would cause
> 1) the incorrect but consistent number when incrementing and scanning simultaneously
> 2) the random number reset and its relationship with compaction of the table
> Keep in mind that most of the hbase settings are at default.
> Thanks!
> p.s. I ran a smaller experiment using hbase shell, and found the counters to be consistent
even for the high rate counters.  I am wondering if there is a buffering issue with the htable
scanner object if it is unable to obtain a lock on the row it will default to the data on

Todd Lipcon
Software Engineer, Cloudera

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