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From Enis Söztutar <enis....@gmail.com>
Subject Re: Merge and HMerge
Date Wed, 16 Nov 2016 19:04:41 GMT
@Appy what is not clear from above?

I think we should get rid of both Merge and HMerge.

We should not have any tool which will work in offline mode by going over
the HDFS data. Seems very brittle to be broken when things get changed.
Only use case I can think of is that somehow you end up with a lot of
regions and you cannot bring the cluster back up because of OOMs, etc and
you have to reduce the number of regions in offline mode. However, we did
not see this kind of thing in any of our customers for the last couple of
years so far.

I think we should seriously look into improving normalizer and enabling
that by default for all the tables. Ideally, normalizer should be running
much more frequently, and should be configured with higher-level goals and
heuristics. Like on average how many regions per node, etc and should be
looking at the global state (like the balancer) to decide on split / merge
points.

Enis

On Wed, Nov 16, 2016 at 1:17 AM, Apekshit Sharma <appy@cloudera.com> wrote:

> bq. HMerge can merge multiple regions by going over the list of
> regions and checking
> their sizes.
> bq. But both of these tools (Merge and HMerge) are very dangerous
>
> I came across HMerge and it looks like dead code. Isn't referenced from
> anywhere except one test. (This is what lars also pointed out in the first
> email too).
> It would make perfect sense if it was a tool or was being referenced from
> somewhere, but with lack of either of that, am a bit confused here.
> @Enis, you seem to know everything about them, please educate me.
> Thanks
> - Appy
>
>
>
> On Thu, Sep 29, 2016 at 12:43 AM, Enis Söztutar <enis.soz@gmail.com>
> wrote:
>
> > Merge has very limited usability singe it can do a single merge and can
> > only run when HBase is offline.
> > HMerge can merge multiple regions by going over the list of regions and
> > checking their sizes.
> > And of course we have the "supported" online merge which is the shell
> > command.
> >
> > But both of these tools (Merge and HMerge) are very dangerous I think. I
> > would say we should deprecate both to be replaced by the online merger
> > tool. We should not allow offline merge at all. I fail to see the usecase
> > that you have to use an offline merge.
> >
> > Enis
> >
> > On Wed, Sep 28, 2016 at 7:32 AM, Lars George <lars.george@gmail.com>
> > wrote:
> >
> > > Hey,
> > >
> > > Sorry to resurrect this old thread, but working on the book update, I
> > > came across the same today, i.e. we have Merge and HMerge. I tried and
> > > Merge works fine now. It is also the only one of the two flagged as
> > > being a tool. Should HMerge be removed? At least deprecated?
> > >
> > > Cheers,
> > > Lars
> > >
> > >
> > > On Thu, Jul 7, 2011 at 2:03 AM, Ted Yu <yuzhihong@gmail.com> wrote:
> > > >>> there is already an issue to do this but not revamp of these Merge
> > > > classes
> > > > I guess the issue is HBASE-1621
> > > >
> > > > On Wed, Jul 6, 2011 at 2:28 PM, Stack <stack@duboce.net> wrote:
> > > >
> > > >> Yeah, can you file an issue Lars.  This stuff is ancient and needs
> to
> > > >> be redone AND redone so we can do merging while table is online
> (there
> > > >> is already an issue to do this but not revamp of these Merge
> classes).
> > > >>  The unit tests for Merge are also all junit3 and do whacky stuff
to
> > > >> put up multiple regions.  This should be redone too (they are often
> > > >> first thing broke when major change and putting them back together
> is
> > > >> a headache since they do not follow the usual pattern).
> > > >>
> > > >> St.Ack
> > > >>
> > > >> On Sun, Jul 3, 2011 at 12:38 AM, Lars George <lars.george@gmail.com
> >
> > > >> wrote:
> > > >> > Hi Ted,
> > > >> >
> > > >> > The log is from an earlier attempt, I tried this a few times.
This
> > is
> > > all
> > > >> local, after rm'ing the /hbase. So the files are all pretty empty,
> but
> > > since
> > > >> I put data in I was assuming it should work. Once you gotten into
> this
> > > >> state, you also get funny error messages in the shell:
> > > >> >
> > > >> > hbase(main):001:0> list
> > > >> > TABLE
> > > >> > 11/07/03 09:36:21 INFO ipc.HBaseRPC: Using
> > > >> org.apache.hadoop.hbase.ipc.WritableRpcEngine for
> > > >> org.apache.hadoop.hbase.ipc.HMasterInterface
> > > >> >
> > > >> > ERROR: undefined method `map' for nil:NilClass
> > > >> >
> > > >> > Here is some help for this command:
> > > >> > List all tables in hbase. Optional regular expression parameter
> > could
> > > >> > be used to filter the output. Examples:
> > > >> >
> > > >> >  hbase> list
> > > >> >  hbase> list 'abc.*'
> > > >> >
> > > >> >
> > > >> > hbase(main):002:0>
> > > >> >
> > > >> > I am assuming this is collateral, but why? The UI works but the
> > table
> > > is
> > > >> gone too.
> > > >> >
> > > >> > Lars
> > > >> >
> > > >> > On Jul 2, 2011, at 10:55 PM, Ted Yu wrote:
> > > >> >
> > > >> >> There is TestMergeTool which tests Merge.
> > > >> >>
> > > >> >> From the log you provided, I got a little confused as why
> > > >> >> 'testtable,row-20,1309613053987.23a35ac696bdf4a8023dcc4c5b8419
> e0.'
> > > >> didn't
> > > >> >> appear in your command line or the output from .META. scanning.
> > > >> >>
> > > >> >> On Sat, Jul 2, 2011 at 10:36 AM, Lars George <
> > lars.george@gmail.com>
> > > >> wrote:
> > > >> >>
> > > >> >>> Hi,
> > > >> >>>
> > > >> >>> These two seem both in a bit of a weird state: HMerge
is scoped
> > > package
> > > >> >>> local, therefore no one but the package can call the
merge()
> > > >> functions...
> > > >> >>> and no one does that but the unit test. But it would
be good to
> > have
> > > >> this on
> > > >> >>> the CLI and shell as a command (and in the shell maybe
with a
> > > >> confirmation
> > > >> >>> message?), but it is not available AFAIK.
> > > >> >>>
> > > >> >>> HMerge can merge regions of tables that are disabled.
It also
> > merges
> > > >> all
> > > >> >>> that qualify, i.e. where the merged region is less than
or equal
> > of
> > > >> half the
> > > >> >>> configured max file size.
> > > >> >>>
> > > >> >>> Merge on the other hand does have a main(), so can be
invoked:
> > > >> >>>
> > > >> >>> $ hbase org.apache.hadoop.hbase.util.Merge
> > > >> >>> Usage: bin/hbase merge <table-name> <region-1>
<region-2>
> > > >> >>>
> > > >> >>> Note how the help insinuates that you can use it as a
tool, but
> > > that is
> > > >> not
> > > >> >>> correct. Also, it only merges two given regions, and
the cluster
> > > must
> > > >> be
> > > >> >>> shut down (only the HBase daemons). So that is a step
back.
> > > >> >>>
> > > >> >>> What is worse is that I cannot get it to work. I tried
in the
> > shell:
> > > >> >>>
> > > >> >>> hbase(main):001:0> create 'testtable', 'colfam1',
 {SPLITS =>
> > > >> >>> ['row-10','row-20','row-30','row-40','row-50']}
> > > >> >>> 0 row(s) in 0.2640 seconds
> > > >> >>>
> > > >> >>> hbase(main):002:0> for i in '0'..'9' do for j in '0'..'9'
do put
> > > >> >>> 'testtable', "row-#{i}#{j}", "colfam1:#{j}", "#{j}" end
end
> > > >> >>> 0 row(s) in 1.0450 seconds
> > > >> >>>
> > > >> >>> hbase(main):003:0> flush 'testtable'
> > > >> >>> 0 row(s) in 0.2000 seconds
> > > >> >>>
> > > >> >>> hbase(main):004:0> scan '.META.', { COLUMNS =>
> > ['info:regioninfo']}
> > > >> >>> ROW                                  COLUMN+CELL
> > > >> >>> testtable,,1309614509037.612d1e0112 column=info:regioninfo,
> > > >> >>> timestamp=130...
> > > >> >>> 406e6c2bb482eeaec57322.             STARTKEY => '',
ENDKEY =>
> > > 'row-10'
> > > >> >>> testtable,row-10,1309614509040.2fba column=info:regioninfo,
> > > >> >>> timestamp=130...
> > > >> >>> fcc9bc6afac94c465ce5dcabc5d1.       STARTKEY => 'row-10',
ENDKEY
> > =>
> > > >> >>> 'row-20'
> > > >> >>> testtable,row-20,1309614509041.e7c1 column=info:regioninfo,
> > > >> >>> timestamp=130...
> > > >> >>> 6267eb30e147e5d988c63d40f982.       STARTKEY => 'row-20',
ENDKEY
> > =>
> > > >> >>> 'row-30'
> > > >> >>> testtable,row-30,1309614509041.a9cd column=info:regioninfo,
> > > >> >>> timestamp=130...
> > > >> >>> e1cbc7d1a21b1aca2ac7fda30ad8.       STARTKEY => 'row-30',
ENDKEY
> > =>
> > > >> >>> 'row-40'
> > > >> >>> testtable,row-40,1309614509041.d458 column=info:regioninfo,
> > > >> >>> timestamp=130...
> > > >> >>> 236feae097efcf33477e7acc51d4.       STARTKEY => 'row-40',
ENDKEY
> > =>
> > > >> >>> 'row-50'
> > > >> >>> testtable,row-50,1309614509041.74a5 column=info:regioninfo,
> > > >> >>> timestamp=130...
> > > >> >>> 7dc7e3e9602d9229b15d4c0357d1.       STARTKEY => 'row-50',
ENDKEY
> > =>
> > > ''
> > > >> >>> 6 row(s) in 0.0440 seconds
> > > >> >>>
> > > >> >>> hbase(main):005:0> exit
> > > >> >>>
> > > >> >>> $ ./bin/stop-hbase.sh
> > > >> >>>
> > > >> >>> $ hbase org.apache.hadoop.hbase.util.Merge testtable
\
> > > >> >>> testtable,row-20,1309614509041.e7c16267eb30e147e5d988c63d40f9
> 82.
> > \
> > > >> >>> testtable,row-30,1309614509041.a9cde1cbc7d1a21b1aca2ac7fda30a
> d8.
> > > >> >>>
> > > >> >>> But I get consistently errors:
> > > >> >>>
> > > >> >>> 11/07/02 07:20:49 INFO util.Merge: Merging regions
> > > >> >>> testtable,row-20,1309613053987.23a35ac696bdf4a8023dcc4c5b8419
> e0.
> > > and
> > > >> >>> testtable,row-30,1309613053987.3664920956c30ac5ff2a7726e4e6
in
> > > table
> > > >> >>> testtable
> > > >> >>> 11/07/02 07:20:49 INFO wal.HLog: HLog configuration:
> blocksize=32
> > > MB,
> > > >> >>> rollsize=30.4 MB, enabled=true, optionallogflushinternal=1000ms
> > > >> >>> 11/07/02 07:20:49 INFO wal.HLog: New hlog
> > > >> >>>
> > > >> /Volumes/Macintosh-HD/Users/larsgeorge/.logs_1309616449171/hlog.
> > > 1309616449181
> > > >> >>> 11/07/02 07:20:49 INFO wal.HLog: getNumCurrentReplicas--HDFS-
> 826
> > > not
> > > >> >>> available; hdfs_out=org.apache.hadoop.fs.
> > > FSDataOutputStream@25961581,
> > > >> >>>
> > > >> exception=org.apache.hadoop.fs.ChecksumFileSystem$
> > > ChecksumFSOutputSummer.getNumCurrentReplicas()
> > > >> >>> 11/07/02 07:20:49 INFO regionserver.HRegion: Setting
up
> > > tabledescriptor
> > > >> >>> config now ...
> > > >> >>> 11/07/02 07:20:49 INFO regionserver.HRegion: Onlined
> > > >> -ROOT-,,0.70236052;
> > > >> >>> next sequenceid=1
> > > >> >>> info: null
> > > >> >>> region1: [B@48fd918a
> > > >> >>> region2: [B@7f5e2075
> > > >> >>> 11/07/02 07:20:49 FATAL util.Merge: Merge failed
> > > >> >>> java.io.IOException: Could not find meta region for
> > > >> >>> testtable,row-20,1309613053987.23a35ac696bdf4a8023dcc4c5b8419
> e0.
> > > >> >>>       at
> > > >> >>> org.apache.hadoop.hbase.util.Merge.mergeTwoRegions(Merge.
> > java:211)
> > > >> >>>       at org.apache.hadoop.hbase.util.Merge.run(Merge.java:111)
> > > >> >>>       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.
> > java:65)
> > > >> >>>       at org.apache.hadoop.hbase.util.
> Merge.main(Merge.java:386)
> > > >> >>> 11/07/02 07:20:49 INFO regionserver.HRegion: Setting
up
> > > tabledescriptor
> > > >> >>> config now ...
> > > >> >>> 11/07/02 07:20:49 INFO regionserver.HRegion: Onlined
> > > >> .META.,,1.1028785192;
> > > >> >>> next sequenceid=1
> > > >> >>> 11/07/02 07:20:49 INFO regionserver.HRegion: Closed
> > > -ROOT-,,0.70236052
> > > >> >>> 11/07/02 07:20:49 INFO wal.HLog: main.logSyncer exiting
> > > >> >>> 11/07/02 07:20:49 ERROR util.Merge: exiting due to error
> > > >> >>> java.lang.NullPointerException
> > > >> >>>       at
> > > >> org.apache.hadoop.hbase.util.Merge$1.processRow(Merge.java:119)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.util.MetaUtils.scanMetaRegion(
> > > MetaUtils.java:229)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.util.MetaUtils.scanMetaRegion(
> > > MetaUtils.java:258)
> > > >> >>>       at org.apache.hadoop.hbase.util.Merge.run(Merge.java:116)
> > > >> >>>       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.
> > java:65)
> > > >> >>>       at org.apache.hadoop.hbase.util.
> Merge.main(Merge.java:386)
> > > >> >>>
> > > >> >>> After which I most of the times have shot .META. with
an error
> > > >> >>>
> > > >> >>> 2011-07-02 06:42:10,763 WARN org.apache.hadoop.hbase.
> > > master.HMaster:
> > > >> Failed
> > > >> >>> getting all descriptors
> > > >> >>> java.io.FileNotFoundException: No status for
> > > >> >>> hdfs://localhost:8020/hbase/.corrupt
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.util.FSUtils.getTableInfoModtime(
> > > FSUtils.java:888)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.util.FSTableDescriptors.get(
> > > FSTableDescriptors.java:122)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.util.FSTableDescriptors.getAll(
> > > FSTableDescriptors.java:149)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.master.HMaster.
> getHTableDescriptors(HMaster.
> > > java:1429)
> > > >> >>>       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native
> > > Method)
> > > >> >>>       at
> > > >> >>>
> > > >> sun.reflect.NativeMethodAccessorImpl.invoke(
> > > NativeMethodAccessorImpl.java:39)
> > > >> >>>       at
> > > >> >>>
> > > >> sun.reflect.DelegatingMethodAccessorImpl.invoke(
> > > DelegatingMethodAccessorImpl.java:25)
> > > >> >>>       at java.lang.reflect.Method.invoke(Method.java:597)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server.call(
> > > WritableRpcEngine.java:312)
> > > >> >>>       at
> > > >> >>>
> > > >> org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(
> > > HBaseServer.java:1065)
> > > >> >>>
> > > >> >>> Lars
> > > >> >
> > > >> >
> > > >>
> > >
> >
>
>
>
> --
>
> -- Appy
>

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