FAQ
Hi Cosmin,
https://issues.apache.org/jira/browse/HBASE-4485 might be applicable.

The patch was included in the fix for 2856.

Cheers,
-Amit

________________________________________
From: Cosmin Lehene [clehene@adobe.com]
Sent: Tuesday, February 14, 2012 12:02 PM
To: dev@hbase.apache.org
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?

Thanks,
Cosmin
On 2/6/12 6:25 PM, "Cosmin Lehene" wrote:

Thanks Ted!

I wonder if it would make more sense to port it to 0.90.X or upgrade to
0.92.

Cosmin
On 2/2/12 5:03 PM, "Ted Yu" wrote:

HBASE-4838 ports HBASE-2856 to 0.92

FYI
On Thu, Feb 2, 2012 at 4:46 PM, Cosmin Lehene 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
the
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
missing
rows.

We're getting this behavior consistently although I couldn't figure a
way
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
to
what I'm seeing? If so it could help me reproduce it.

Thanks,
Cosmin



On 2/1/12 11:30 PM, "Jonathan Hsieh" wrote:

Cosmin,

How many column families to you have in this table? Are you using any
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 <clehene@adobe.com>
wrote:
We have a MR job that runs every few minutes on some time series
data
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
persist
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
it's
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
this
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)
on
top
of Hadoop cdh3u2.

Cosmin



--
// Jonathan Hsieh (shay)
// Software Engineer, Cloudera
// jon@cloudera.com

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