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From Young <youngma...@gmail.com>
Subject Re: counters and scanners inconsistency
Date Wed, 18 Jan 2012 18:52:14 GMT
Hello Todd,

Thanks for pointing this out for me.  The client was running 0.90.1, while the cluster was
running 0.90.3.  I upgraded both to the latest CDH3 distro version, 0.90.4, and the problem
seems to have gone away (simultaneous scanner + inc produces consistent results).  I still
don't know what the root of the problem was, but this simple upgrade was enough to fix it.

Thanks!

On Jan 16, 2012, at 6:21 PM, Todd Lipcon wrote:

> 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.
> 
> -Todd
> 
> 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 values.
>> 
>> 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
disk?
>> 
> 
> 
> 
> -- 
> Todd Lipcon
> Software Engineer, Cloudera


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