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HBase >> mail # dev >> MR job "randomly" scans up thousands of rows less than the it should.

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RE: MR job "randomly" scans up thousands of rows less than the it should.
Hi Cosmin,
  https://issues.apache.org/jira/browse/HBASE-4485 might be applicable.

  The patch was included in the fix for 2856.


From: Cosmin Lehene [[EMAIL PROTECTED]]
Sent: Tuesday, February 14, 2012 12:02 PM
Subject: Re: MR job "randomly" scans up thousands of rows less than the it should.

I just got back on this issue. Initially the behavior we've seen (missing
rows) wouldn't reproduce on 0.90 using TestAcidGuarantees.
However, if the puts in the writer threads include additional rows the
scanners will start reading less rows. This reproduces consistently on
0.90 and seems to be working correctly on 0.92.

HBASE-2856/HBASE-4838 are probably the solution, although there's a chance
it's some other fix on 0.92 (ideas?)

We're undecided whether backporting to 0.90 vs upgrading the affected
clusters to 0.92 would be better?
Also is there interest for this fix on 0.90?


On 2/6/12 6:25 PM, "Cosmin Lehene" <[EMAIL PROTECTED]> wrote:

>Thanks Ted!
>I wonder if it would make more sense to port it to 0.90.X or upgrade to
>On 2/2/12 5:03 PM, "Ted Yu" <[EMAIL PROTECTED]> wrote:
>>HBASE-4838 ports HBASE-2856 to 0.92
>>On Thu, Feb 2, 2012 at 4:46 PM, Cosmin Lehene <[EMAIL PROTECTED]> wrote:
>>> (sorry for the damaged subject :))
>>> Hey Jon,
>>> We have two column families.
>>> There are no filters and there's a full table scan. We're not skipping
>>> rows.
>>> I did see however a single time that we had one qualifier "fault" in
>>> job counters (it was missing, and it wasn't supposed to be missing).
>>> However that was only once and it doesn't happen when we encounter
>>> rows.
>>> We're getting this behavior consistently although I couldn't figure a
>>> to reproduce it. I'll try running multiple instances of the job in
>>> parallel to figure out if that would affect the outcome.
>>> I'll probably have to add more debugging for the affected rows and dig
>>> deeper.
>>> HBASE-2856 is a pretty large issue - do you think it could be related
>>> what I'm seeing? If so it could help me reproduce it.
>>> Thanks,
>>> Cosmin
>>> On 2/1/12 11:30 PM, "Jonathan Hsieh" <[EMAIL PROTECTED]> wrote:
>>> >Cosmin,
>>> >
>>> >How many column families to you have in this table?   Are you using
>>> >filters in you HBase scans?  Are you using skip rows that may not have
>>> >qualifiers present?
>>> >
>>> >There are a few known issues with multi-CF atomicity and a recent one
>>> >about
>>> >flushes that may be related to this problem.  There HBASE-2856, a fix
>>> >having to do with flushes which is pretty intricate and only in 0.92.
>>> >
>>> >Jon.
>>> >
>>> >On Wed, Feb 1, 2012 at 8:46 PM, Cosmin Lehene <[EMAIL PROTECTED]>
>>> >
>>> >> We have a MR job that runs every few minutes on some time series
>>> >> which is continuously updated (never deleted).
>>> >> Every few (in the range of tens to hundreds) runs the map task that
>>> >>covers
>>> >> the last region will get fewer input records (off by 500-5000 rows)
>>> >>without
>>> >> any splits happening. This lower number of input records could
>>> >>for
>>> >> a few MR runs, but will eventually get back to the "correct" value.
>>> >>
>>> >> This drop can be seen both in the "map input records" metric but
>>> >> correlated with the metrics that get computed by the MR job (so it's
>>> >>not a
>>> >> MR counter bug).
>>> >>
>>> >> There are no exceptions in the MR job, or in the region server and
>>> >> doesn't seem to be correlated with any compaction, split or region
>>> >>movement.
>>> >> The only "variable" in this scenario is that new data gets injected
>>> >> continuously (and the actual MR job which is idempotent)
>>> >>
>>> >> This entire puzzle takes place on  HBase 0.90.5 ­ish (12 dec 2011)
>>> >>top
>>> >> of Hadoop cdh3u2.
>>> >>
>>> >> Cosmin