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From "Ramkrishna.S.Vasudevan" <ramkrishna.vasude...@huawei.com>
Subject RE: A general question on maxVersion handling when we have Secondary index tables
Date Thu, 30 Aug 2012 04:34:24 GMT
Reg , the collocation part of the main table regions and index table
regions, that is pretty much necessary. 

Reg, how secondary index feature can be supported either as external or
core-> I would say that seeing the current things that we have done it can
be like security means secondary index can be supplied along with the core
and if we base our impl based on coprocessors overall changes to the kernel
seems to be minimal and if we are ok in having secondary index feature along
with the core then those changes become inevitable and at the same time
useful too.

Regards
Ram
> -----Original Message-----
> From: Ted Yu [mailto:yuzhihong@gmail.com]
> Sent: Wednesday, August 29, 2012 9:50 PM
> To: dev@hbase.apache.org
> Subject: Re: A general question on maxVersion handling when we have
> Secondary index tables
> 
> For the secondary index based on state portion of address example, I
> wonder
> if we can achieve comparable performance using scan with proper filter.
> 
> Cheers
> 
> On Wed, Aug 29, 2012 at 9:11 AM, Jonathan Hsieh <jon@cloudera.com>
> wrote:
> 
> > Ted,
> >
> > Ram's summarizes the concern succinctly -- to answer the specific
> question
> > it isn't for versions -- it is for the case where a secondary index
> can
> > point to many many primary rows.  (let's say we have a rowkey userid
> and we
> > want to have a 2ndary index based on the state portion of there
> address
> >  --- we'll end up pointing to many many primary rows).
> >
> > Jon.
> >
> >
> >
> > On Wed, Aug 29, 2012 at 7:15 AM, Ted Yu <yuzhihong@gmail.com> wrote:
> >
> > > Thanks for the detailed response, Jon.
> > >
> > > bq. it would mean that a query based on secondary index would
> > > potentially have to hit every region server that has a region in
> the
> > > primary table.
> > >
> > > Can you elaborate on the above a little bit ?
> > > Is this because secondary index would point us to more than one
> region in
> > > the data table because several versions are saved for the same row
> ?
> > >
> > > My thinking was to ease management of simultaneous (data and index)
> > region
> > > split through region colocation.
> > >
> > > Cheers
> > >
> > > On Wed, Aug 29, 2012 at 6:47 AM, Jonathan Hsieh <jon@cloudera.com>
> > wrote:
> > >
> > > > I'm more of a fan of having secondary indexes added as an
> external
> > > feature
> > > > (coproc or new client library on top of our current client
> library) and
> > > > focusing on only adding apis necessary to make 2ndary indexes
> possible
> > > and
> > > > correct on/in HBase.  There are many different use patterns and
> > > > requirements and one style of secondary index will not be good
> for
> > > > everything.  Do we only care about this working well for highly
> > > selectivity
> > > > keys?  What are possible indexes (col name, value, value prefix,
> > > everything
> > > > our filters support?)  Do we care more about writes or reads,
> ACID
> > > > correctness or speed, etc?  Also, there are several questions
> about how
> > > we
> > > > handle other features in conjunction with 2ndary indexes:
> replication,
> > > bulk
> > > > load, snapshots, to name a few.
> > > >
> > > > Maybe it makes sense to spend some time defining what we want to
> index
> > > > secondarily and what a user api to this external api would be.
> Then we
> > > > could have the different implementations under-the-covers, and
> allow
> > for
> > > > users to swap implementations for the tradeoffs that fit their
> use
> > cases.
> > > >  It wouldn't be free to change but hopefully "easy" from a user
> point
> > of
> > > > view.
> > > >
> > > > Personally, I've tend to favor more of a percolator-style
> > implementation
> > > --
> > > > it is a client library and built on top of hbase. This approach
> seems
> > to
> > > be
> > > > more "HBase-style" with it's emphasis consistency and atomicity,
> and
> > > seems
> > > > to require only a few mondifications to HBase core. Sure it
> likely
> > slower
> > > > than my read of Jesse's proposal, but it seems always always
> consistent
> > > and
> > > > thus predictable in cases where there are failures on deletes and
> > > updates.
> > > > We'd need  HBase API primitives like checkAndMutate call (check
> with
> > > > multiple delete/put on the same row), and possibly an atomic
> multitable
> > > > bulkload.  I'm not sure that it is replication compatible, and
> there
> > are
> > > > probably questions we'll need to answer once snapshots
> solidifies.
> > > >
> > > > Ted's idea of colocating regions (like the index table's
> > > > regions) definitely feels like a primitive (pluggable, likely-
> per-table
> > > > region assignment plans) that we could add to HBase core. This
> > > requirement
> > > > though for 2ndary indexes seems to imply an approach similar to
> > > cassandra's
> > > > approach -- having a local index of each region on region server
> and
> > > > colocating them.  Is this right?  If so, this is essentially a
> > filtering
> > > > optimization --  it would mean that a query based on secondary
> index
> > > would
> > > > potentially have to hit every region server that has a region in
> the
> > > > primary table.  This is great approach if the index lookup has
> high
> > > > cardinality but if the secondary index is highly selective, you'd
> have
> > to
> > > > march through a bunch or RS's before getting an answer.
> > > >
> > > > Jon.
> > > >
> > > > On Tue, Aug 28, 2012 at 9:18 PM, Ramkrishna.S.Vasudevan <
> > > > ramkrishna.vasudevan@huawei.com> wrote:
> > > >
> > > > > Hi
> > > > >
> > > > > Yes I was talking about the dead entry in the index table
> rather than
> > > the
> > > > > actual data table.
> > > > >
> > > > > Regards
> > > > > Ram
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Wei Tan [mailto:wtan@us.ibm.com]
> > > > > > Sent: Tuesday, August 28, 2012 9:22 PM
> > > > > > To: dev@hbase.apache.org
> > > > > > Cc: Sandeep Tata
> > > > > > Subject: Re: A general question on maxVersion handling when
> we have
> > > > > > Secondary index tables
> > > > > >
> > > > > > Thanks for sharing a pointer to your implementation.
> > > > > > My two cents:
> > > > > > timestamp is a way to do MVCC and setting every KV with the
> same TS
> > > > > > will
> > > > > > get concurrency control very tricky and error prone, if not
> > > impossible
> > > > > > I think Ram is talking about the dead entry in the index
> table
> > rather
> > > > > > than
> > > > > > data table. Deleting old index entries upfront when there is
> a new
> > > put
> > > > > > might be a choice.
> > > > > >
> > > > > >
> > > > > > Best Regards,
> > > > > > Wei
> > > > > >
> > > > > > Wei Tan
> > > > > > Research Staff Member
> > > > > > IBM T. J. Watson Research Center
> > > > > > 19 Skyline Dr, Hawthorne, NY  10532
> > > > > > wtan@us.ibm.com; 914-784-6752
> > > > > >
> > > > > >
> > > > > >
> > > > > > From:   Jesse Yates <jesse.k.yates@gmail.com>
> > > > > > To:     dev@hbase.apache.org,
> > > > > > Date:   08/28/2012 04:00 AM
> > > > > > Subject:        Re: A general question on maxVersion handling
> when
> > we
> > > > > > have
> > > > > > Secondary index tables
> > > > > >
> > > > > >
> > > > > >
> > > > > > Ram,
> > > > > >
> > > > > > If I understand correctly, I think you can design your index
> such
> > > that
> > > > > > you
> > > > > > don't actually use the timestamp (e.g. everything gets put
> with a
> > TS
> > > =
> > > > > > 10
> > > > > > -
> > > > > > or some other non-special, relatively small number that's not
> 0 as
> > > I'd
> > > > > > worry about that in HBase ;) Then when you set maxVersions to
> 1,
> > > > > > everything
> > > > > > should be good.
> > > > > >
> > > > > > You get a couple of wasted bytes from the TS, but with the
> > prefixTrie
> > > > > > stuff
> > > > > > that should be pretty minimal overhead. If you do need to
> keep
> > track
> > > of
> > > > > > the
> > > > > > timestamp you should be able to munge that back up into the
> column
> > > > > > qualifier (and just know that that last 64 bits is the
> timestamp).
> > > > > > Again a
> > > > > > little more CPU cost, but its really not that big of an
> overhead.
> > It
> > > > > > seems
> > > > > > like you don't really care about the TS though, in which case
> this
> > > > > > should
> > > > > > be pretty simple.
> > > > > >
> > > > > > Out of curiosity, what are people using for their secondary
> > indexing
> > > > > > solutions? I know there are a bunch out there, but don't know
> what
> > > > > > people
> > > > > > have adopted, what they like/dislike, design tradeoffs made
> and
> > why.
> > > > > >
> > > > > > Disclaimer: I recently proposed a secondary indexing solution
> > myself
> > > > > > (shameless self-plug:
> > > > > > http://jyates.github.com/2012/07/09/consistent-enough-
> secondary-
> > > > > > indexes.html
> > > > > > )
> > > > > > and its something I'm working on for Salesforce - open
> sourced at
> > > some
> > > > > > point, promise!
> > > > > >
> > > > > > -Jesse
> > > > > > -------------------
> > > > > > Jesse Yates
> > > > > > @jesse_yates
> > > > > > jyates.github.com
> > > > > >
> > > > > >
> > > > > > On Tue, Aug 28, 2012 at 12:24 AM, Ramkrishna.S.Vasudevan <
> > > > > > ramkrishna.vasudevan@huawei.com> wrote:
> > > > > >
> > > > > > > Hi All
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > When we try to build any type of secondary indices for
a
> given
> > > table
> > > > > > how
> > > > > > > can
> > > > > > > one handle maxVersions in the secondary index tables.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > For eg,
> > > > > > >
> > > > > > > I have inserted
> > > > > > >
> > > > > > >  Row1  -  Val1  => t
> > > > > > >
> > > > > > > Row1 - Val2 => t+1
> > > > > > >
> > > > > > > Row1 - Val3. => t+2
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Ideally if my max versions is only one then Val3 should
be
> my
> > > result
> > > > > > If
> > > > > > I
> > > > > > > query on main table for row1.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Now in my index I will be having all the above 3 entries.
> Now
> > how
> > > > > > can
> > > > > > we
> > > > > > > remove the older entries from the index table that does
not
> fit
> > > into
> > > > > > > maxVersions.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Currently while scanning and the code that avoids the max
> > Versions
> > > > > > does
> > > > > > not
> > > > > > > give any hooks to know the entries skipped thro versions.
> > > > > > >
> > > > > > > So any suggestions on this, I am still seeing the code
for
> any
> > > other
> > > > > > > options
> > > > > > > but suggestions welcome.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Regards
> > > > > > >
> > > > > > > Ram
> > > > > > >
> > > > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > > --
> > > > // Jonathan Hsieh (shay)
> > > > // Software Engineer, Cloudera
> > > > // jon@cloudera.com
> > > >
> > >
> >
> >
> >
> > --
> > // Jonathan Hsieh (shay)
> > // Software Engineer, Cloudera
> > // jon@cloudera.com
> >


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