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From Shengjie Min <kelvin....@gmail.com>
Subject Re: HBase - Secondary Index
Date Thu, 27 Dec 2012 13:07:20 GMT
Thanks, Anoop, That makes sense. Hope you guys make this open source soon.
This model seems working ok if the resultSet is not huge, you get the main
keys and re-seek exact rows from the main table. But One thing concerns me
a little bit is that after querying the index table, you get a resultSet of
the main keys is very big, how the massive number of get() is going to
perform againt the main table, becoz potentially the results can be
scattered to all different regions.

- Shengjie


On 27 December 2012 11:30, Anoop Sam John <anoopsj@huawei.com> wrote:

>
> >What happens when regions get splitted ? do you update the startkey on the
> index table?
>
> We have a custom HalfStoreFileReader to read the split index region data.
> This reader will change the rowkey it returns with replacing the startkey
> part.
> After a split immediately HBase will initiate a compaction and the
> compation uses this new reader. So the rowkey coming out will be a changed
> one and thus the newly written HFiles will have the changed rowkey.  Also a
> normal read (as part of scan) during this time uses this new reader and so
> we will always get the rowkey in the expected format..  :)   Hope I make it
> clear for you.
>
> -Anoop-
> ________________________________________
> From: Shengjie Min [kelvin.msj@gmail.com]
> Sent: Thursday, December 27, 2012 4:53 PM
> To: user@hbase.apache.org
> Subject: Re: HBase - Secondary Index
>
> Hi Anoop,
>
> >First all there will be same number of regions in both primary and index
> tables. All the start/stop keys of the regions also will be same.
> >Suppose there are 2 regions on main table say for keys 0-10 and 10-20.
>  Then we will create 2 regions in index table also with same key ranges.
> >At the master balancing level it is easy to collocate these regions seeing
> the start and end keys.
> >When the selection of the rowkey that will be used in the index table is
> the key here.
> >What we will do is all the rowkeys in the index table will be prefixed
> with the start key of the region/
> >When an entry is added to the main table with rowkey as 5 it will go to
> the 1st region (0-10)
> >Now there will be index region with range as 0-10.  We will select this
> region to store this index data.
> >The row getting added into the index region for this entry will have a
> rowkey 0_x_5
> >I am just using '_' as a seperator here just to show this. Actually we
> wont be having any seperator.
> >So the rowkeys (in index region) will have a static begin part always.
>  Will scan time also we know this part and so the startrow and endrow
> creation for the scan will be possible.. Note that we will store the actual
> table row >key as the last part of the index rowkey itself not as a value.
> >This is better option in our case of handling the scan index usage also at
> sever side.  There is no index data fetch to client side..
>
> What happens when regions get splitted ? do you update the startkey on the
> index table?
>
> -Shengjie
>
>
> On 14 December 2012 08:54, Anoop Sam John <anoopsj@huawei.com> wrote:
>
> > Hi Anil,
> >
> > >1. In your presentation you mentioned that region of Primary Table and
> > Region of Secondary Table are always located on the same region server.
> How
> > do you achieve it? By using the Primary table rowkey as prefix of  Rowkey
> > of Secondary Table? Will your implementation work if the rowkey of
> primary
> > table cannot be used as prefix in rowkey of Secondary table( i have this
> > limitation in my use case)?
> > First all there will be same number of regions in both primary and index
> > tables. All the start/stop keys of the regions also will be same.
> > Suppose there are 2 regions on main table say for keys 0-10 and 10-20.
> >  Then we will create 2 regions in index table also with same key ranges.
> > At the master balancing level it is easy to collocate these regions
> seeing
> > the start and end keys.
> > When the selection of the rowkey that will be used in the index table is
> > the key here.
> > What we will do is all the rowkeys in the index table will be prefixed
> > with the start key of the region/
> > When an entry is added to the main table with rowkey as 5 it will go to
> > the 1st region (0-10)
> > Now there will be index region with range as 0-10.  We will select this
> > region to store this index data.
> > The row getting added into the index region for this entry will have a
> > rowkey 0_x_5
> > I am just using '_' as a seperator here just to show this. Actually we
> > wont be having any seperator.
> > So the rowkeys (in index region) will have a static begin part always.
> >  Will scan time also we know this part and so the startrow and endrow
> > creation for the scan will be possible.. Note that we will store the
> actual
> > table row key as the last part of the index rowkey itself not as a value.
> > This is better option in our case of handling the scan index usage also
> at
> > sever side.  There is no index data fetch to client side..
> >
> > I feel your use case perfectly fit with our model
> >
> > >2. Are you using an Endpoint or Observer for building the secondary
> index
> > table?
> > Observer
> >
> > >3. "Custom balancer do collocation". Is it a custom load balancer of
> HBase
> > Master or something else?
> > It is a balancer implementation which will be plugged into Master
> >
> > >4. Your region split looks interesting. I dont have much info about it.
> > Can
> > you point to some docs on IndexHalfStoreFileReader?
> > Sorry I am not able to publish any design doc or code as the company has
> > not decided to open src the solution yet.
> > Any particular query you come acorss pls feel free to aske me :)
> > You can see the HalfStoreFileReader class 1st..
> >
> > -Anoop-
> > ________________________________________
> > From: anil gupta [anilgupta84@gmail.com]
> > Sent: Friday, December 14, 2012 2:11 PM
> > To: user@hbase.apache.org
> > Subject: Re: HBase - Secondary Index
> >
> > Hi Anoop,
> >
> > Nice presentation and seems like a smart implementation. Since the
> > presentation only covered bullet points so i have couple of questions on
> > your implementation. :)
> >
> > Here is a recap to my implementation and our previous discussion on
> > Secondary index:
> >
> > Here is the link to previous email thread:
> > http://search-hadoop.com/m/1zWPMaaRtr .
> >
> > The secondary index is stored in table "B" as rowkey B --> family:<rowkey
> > A>  . "<rowkey A>" is the column qualifier. Every row in B will only on
> > have one column "k" and the value of that column is the rowkey of A.
> >
> > Suppose i am storing customer events in table A. I have two requirement
> for
> > data query:
> > 1. Query customer events on basis of customer_Id and event_ID.
> > 2. Query customer events on basis of event_timestamp and customer_ID.
> >
> > 70% of querying is done by query#1, so i will create
> > <customer_Id><event_ID> as row key of Table A.
> > Now, in order to support fast results for query#2, i need to create a
> > secondary index on A. I store that secondary index in B, rowkey of B is
> > <event_timestamp><customer_ID>.Every row stores the corresponding rowkey
> of
> > A.
> >
> > HBase Querying approach:
> > 1. Scan the secondary table by using prefix filter and startRow to get
> the
> > list of Rowkeys of Primary table.
> > 2. Do a batch get on primary table by using HTable.get(List<Get>) method
> > using the list of Rowkeys obtained in step1.
> >
> > The only issue is that in my solution i have at least two RPC calls. Once
> > each in step1 and step2 above. I want to reduce the number of RPC to 1 if
> > possible.
> >
> >
> > ******Questions on your implementation:*********
> >
> > 1. In your presentation you mentioned that region of Primary Table and
> > Region of Secondary Table are always located on the same region server.
> How
> > do you achieve it? By using the Primary table rowkey as prefix of  Rowkey
> > of Secondary Table? Will your implementation work if the rowkey of
> primary
> > table cannot be used as prefix in rowkey of Secondary table( i have this
> > limitation in my use case)?
> > 2. Are you using an Endpoint or Observer for building the secondary index
> > table?
> > 3. "Custom balancer do collocation". Is it a custom load balancer of
> HBase
> > Master or something else?
> > 4. Your region split looks interesting. I dont have much info about it.
> Can
> > you point to some docs on IndexHalfStoreFileReader?
> >
> > Thanks,
> > Anil Gupta
> >
> >
> >
> > On Tue, Dec 4, 2012 at 12:10 AM, Anoop Sam John <anoopsj@huawei.com>
> > wrote:
> >
> > > Hi All
> > >
> > >             Last week I got a chance to present the secondary indexing
> > > solution what we have done in Huawei at the China Hadoop Conference.
>  You
> > > can see the presentation from
> > > http://hbtc2012.hadooper.cn/subject/track4Anoop%20Sam%20John2.pdf
> > >
> > >
> > >
> > > I would like to hear what others think on this. :)
> > >
> > >
> > >
> > > -Anoop-
> > >
> >
> >
> >
> > --
> > Thanks & Regards,
> > Anil Gupta
> >
>
>
>
> --
> All the best,
> Shengjie Min
>



-- 
All the best,
Shengjie Min

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