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From: Jonathan Hsieh <jon@cloudera.com>
Date: Wed, 27 May 2015 18:27:23 -0700
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Subject: Re: [DISCUSSION] Merge of the hbase-11339 mob branch into master.
To: "dev@hbase.apache.org" <dev@hbase.apache.org>
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On Sat, May 23, 2015 at 9:40 AM, Andrew Purtell <apurtell@apache.org> wrote:

> Regarding performance testing: Whatever has been done on the MOB branch
> will be interesting data points, and, potentially encouraging, but porting
> to branch-1 will produce a new code base. Earlier results on other code
> will not be applicable. We have to start over. Like I said elsewhere, I'm
> happy to help with (re)characterizing the perf impact and improvements
> produced by the changes.
>
>
Thank you for offer for help -- we'd appreciated it!

Although most of my it tests and perf tests results were done against
against trunk (from sept '14 and then later feb '15 -- we've been doing
them roughly every two weeks now) Jingcheng's most recent performance
testing and fault injection testing results were actually done against a
version merged/rebased on to hbase 1.0.0[1].  Though not on the most recent
branch-1, would this be close enough and sufficient or would you still want
to redoing them?

If we want to redo them when we have a 1.x backport is ready to propose,
we'll include the augmented ltt[2] that will make it easy to exercise the
mob feature's performance.

[1] https://github.com/cloudera/hbase/commits/cdh5-1.0.0_5.4.0?page=2
 (this is cdh5.4.0's hbase 1.0.0-based hbase)
[2] https://issues.apache.org/jira/browse/HBASE-13277


What coverage do we have for verifying the integrity of MOB references?
> Will the sweep tool detect, alert on, and optionally repair dangling
> references? (I could answer this for myself by looking at MOB branch, but
> hopefully someone here has an answer at the ready.) I assume we calculate
> and store checksums for MOB data itself so we know if values are corrupt.
> Does the sweep tool detect MOB value corruption? Can it be repaired? Do we
> have a good ops story for why HBCK is no longer sufficient on its own,
> there's a separate tool with a whole new set of options - and a requirement
> for a MR runtime! - for checking MOB data? That last one is a rhetorical
> question (smile), the ops story is... unsatisfying. It's like we've taken a
> self sufficient HBase and bolted in parts of Hive, so now we need MR.
>
> Our internal compaction detects and alerts at warn level if there is a
missing link [3], and then returns a empty value [4]

Mobs are stored in hfiles so we have the same checksumming all other hfiles
have.

In the other response, I answered about hbck and how something like
Hfile.main() could be a more appropriate checking tool to address this
situation.

I'm afraid then much of our complete operational story is "unsatisfying"
even without mob because it still requires MR -- e.g. copytable, export,
import, walplayer, or verifyreplicaion mr jobs. While I'll agree that
having an external system is undesirable and unacceptable for what are
mandatory internal operations like compactions, I think requiring mr for a
verifiymob mr job would as acceptable as the verfiyreplication job.

[3]
https://github.com/apache/hbase/blob/hbase-11339/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HMobStore.java#L400
[4]
https://github.com/apache/hbase/blob/hbase-11339/hbase-server/src/main/java/org/apache/hadoop/hbase/mob/DefaultMobCompactor.java#L224

>
> On Fri, May 22, 2015 at 1:45 PM, Jonathan Hsieh <jon@cloudera.com> wrote:
>
> > In another thread andrew purtell brought up some concerns about the mob
> > feature:
> >
> > On Fri, May 22, 2015 at 12:40 PM, Andrew Purtell <apurtell@apache.org>
> >  wrote:
> >
> > > Another point of clarification, sorry, I hit the send button too early
> it
> > > seems: I don't believe MOB is fully integrated yet, for example the
> > > feature
> > > is an extension to store that lacks support for encryption (this would
> > > technically be a feature regression); and HBCK. I have not been
> following
> > > MOB too closely so could be mistaken. These issues do not preclude a
> > merge
> > > of MOB into trunk, but do preclude a merge back of MOB from trunk to
> > > branch-1. I would veto the latter until such shortcomings in the
> > > implementation that could be described as regressions are addressed. I
> > > would also like to see a performance analysis of a range of workloads
> > > before and after in as much detail as can be mustered, and would be
> happy
> > > to volunteer to help out with that.
> > >
> >
> > Here's info on the points brought up:
> >
> > Encryption support shortcoming is being addrsessed here:
> > https://issues.apache.org/jira/browse/HBASE-13693 (closed)
> > https://issues.apache.org/jira/browse/HBASE-13720 (in review)
> >
> > Hbck has been actually run against the integration test rigs while the
> > feature has been enabled but currently has no explicit unit test or
> simple
> > to run integration test.  It currently doesn't report anything special
> > about the mob storage area. We can add unit tests that cover hbck when
> the
> > mob path is exercised.
> >
> > Another suggestion was a tool to check that mob references had
> > corresponding mob data.  We currently include a mr-based sweeper job that
> > could be used to perform this verification.  We can add this tool and
> > testing for the tool.
> >
> > I've done some performance testing and Jingcheng and his colleagues have
> > done significant amounts of performance testing. We currently have a blog
> > post in progress that will share the results of this performance testing.
> >
> > Jon.
> >
> >
> >
> >
> >
> > On Wed, May 20, 2015 at 7:38 PM, Ted Yu <yuzhihong@gmail.com> wrote:
> >
> > > This is a useful feature, Jon.
> > >
> > > I went over the mega-patch and left some comments on review board.
> > >
> > > I noticed that hbck was not included in the patch. Neither did I find a
> > > sub-task of HBASE-11339 that covers hbck.
> > >
> > > Do you or Jingcheng plan to add MOB-aware capability for hbck ?
> > >
> > > Cheers
> > >
> > > On Wed, May 20, 2015 at 9:21 AM, Jonathan Hsieh <jon@cloudera.com>
> > wrote:
> > >
> > > > Hi folks,
> > > >
> > > > The Medium Object (MOB) Storage feature (HBASE-11339[1]) is modified
> > I/O
> > > > and compaction path that allows individual moderately sized values
> > > > (10k-10MB) to be stored so that write amplification is reduced when
> > > > compared to the normal I/O path.   At a high level, it provides
> > alternate
> > > > flush and compaction mechanisms that segregates large cells into a
> > > separate
> > > > area where they are not subject to potentially frequent compaction
> and
> > > > splits that can be encountered in the normal I/O path. A more
> detailed
> > > > design doc can be found on the hbase-11339 jira.
> > > >
> > > > Jingcheng Du has been working on the mob feature for a while and
> Anoop,
> > > Ram
> > > > and I have been shepherding him through the design revisions and
> > > > implementation of the feature in the hbase-11339 branch.[2]
> > > >
> > > > The branch we are proposing to merge into master is compatible with
> > > HBase's
> > > > core functionality including snapshots, replication, shell support,
> > > behaves
> > > > well with table alters, bulk loads and does not require external MR
> > > > processes. It has been documented, and subject to many integration
> test
> > > > runs  (ITBLL, ITAcidGuarantees, ITIngest) including fault injection.
> > > > Performance testing of the feature shows what can be a 2x-3x
> throughput
> > > > improvement for workloads that contain mobs. These results can be
> seen
> > on
> > > > the hbase 2.0 panel discussion slides from hbasecon (once published).
> > > >
> > > > Recently there have been some hfile encryption related shortcomings
> > that
> > > we
> > > > could address in branch or in master.
> > > >
> > > > Earlier iterations of the feature has been tested in production by
> > users
> > > > that Jingcheng has been responsible for.  A version has also been
> > > deployed
> > > > at users I have been responsible for.  Some of the folks from Huawei
> > > > (ashutosh) have also been submitting the recent encryption bug
> reports
> > > > against the hbase-11339 branch so there is some evidence of usage by
> > > them.
> > > >
> > > > The four of us  (Jingcheng, Ram, Anoop and I) are satisfied with the
> > > > feature and feel it is a good time to call a merge vote.  Ive posted
> a
> > > > megapatch version for folks who want to peruse the code. [3]
> > > >
> > > > What do you all think?
> > > >
> > > > Thanks,
> > > > Jingcheng, Jon, Ram, and Anoop.
> > > >
> > > > [1] https://issues.apache.org/jira/browse/HBASE-11339
> > > > [2] https://github.com/apache/hbase/tree/hbase-11339
> > > > [3] https://reviews.apache.org/r/34475/
> > > > --
> > > > // Jonathan Hsieh (shay)
> > > > // HBase Tech Lead, Software Engineer, Cloudera
> > > > // jon@cloudera.com // @jmhsieh
> > > >
> > >
> >
> >
> >
> > --
> > // Jonathan Hsieh (shay)
> > // HBase Tech Lead, Software Engineer, Cloudera
> > // jon@cloudera.com // @jmhsieh
> >
>
>
>
> --
> Best regards,
>
>    - Andy
>
> Problems worthy of attack prove their worth by hitting back. - Piet Hein
> (via Tom White)
>


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

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