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HBase, mail # user - Pagination with HBase - getting previous page of data


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Re: Pagination with HBase - getting previous page of data
anil gupta 2013-01-25, 17:43
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On Fri, Jan 25, 2013 at 9:17 AM, Jean-Marc Spaggiari <
[EMAIL PROTECTED]> wrote:

> Hi Anil,
>
> The issue is that all the other sub-sequent page start should be moved
> too...
>
Yes, this is a possibility. Hence the Developer has to take care of this
case. It might also be possible that the pageSize is not a hard limit on
number of results(more like a hint or suggestion on size). I would say it
varies by use case.

>
> so if you want to jump directly to page n, you might be totally
> shifted because of all the data inserted in the meantime...
>
> If you want a real complete pagination feature, you might want to have
> a coproccessor or a MR updating another table refering to the
> pages....
>
Well, the solution depends on the use case. I will be doing pagination in
HBase for a restful service but till now i am unable to find any reason why
this cant be done at application level.
Are you suggesting to use MR for paging in HBase? If yes, how?
How would you use another table for pagination?what would you store in the
extra table?

>
> JM
>
> 2013/1/25, anil gupta <[EMAIL PROTECTED]>:
> > Hi Vijay,
> >
> > I've done paging in HBase by using Scan only(no pagination filter) as
> > Mohammed has explained. However it was just an experimental stuff. It
> works
> > but Jean raised a very good point.
> > Find my answer inline to fix the problem that Jean reported.
> >
> >
> > On Fri, Jan 25, 2013 at 4:38 AM, Jean-Marc Spaggiari <
> > [EMAIL PROTECTED]> wrote:
> >
> >> Hi Vijay,
> >>
> >> If, while the user os scrolling forward, you store the key of each
> >> page, then you will be able to go back to a specific page, and jump
> >> forward back up to where he was.
> >>
> >> The only issue is that, if while the user is scrolling the table,
> >> someone insert a row between the last of a page, and the first of the
> >> next page, you will never see this row.
> >>
> >> Let's take this exemaple.
> >>
> >> You have 10 items per page.
> >>
> >> 010 020 030 040 050 060 070 080 090 100 is the first page.
> >> 110 120 130 140 150 160 170 180 190 200 is the second one.
> >>
> >> Now, if someone insert 101... If will be just after 100 and before 110.
> >>
> > Anil: Instead of scanning from 010 to 100, scan from 010 to 110. Then we
> > wont have this problem. So, i mean to say that
> > startRow(firstRowKeyofPage(N)) and stopRow(firstRowKeyofPage(N+1)). This
> > would fix it. Also, in that case number of results might exceed the
> > pageSize. So you might need to handle this logic.
> >
> >>
> >> When you will display 10 rows starting at 010 you will stop just
> >> before 101... And for the next page you will start at 110... And 101
> >> will never be displayed...
> >>
> >> HTH
> >>
> >> JM
> >>
> >> 2013/1/25, Mohammad Tariq <[EMAIL PROTECTED]>:
> >> > Hello sir,
> >> >
> >> >       While paging through, store the startkey of the current page of
> >> > 25
> >> > rows
> >> > in a separate byte[]. Now, if you want to come back to this page when
> >> > you
> >> > are at the next page do a range query where  startkey would be the
> >> > rowkey
> >> > you had stored earlier and the endkey would be the startrowkey  of
> >>  current
> >> > page. You have to store just one rowkey each time you show a page
> using
> >> > which you could come back to this page when you are at the next page.
> >> >
> >> > However, this approach will fail in a case where your user would like
> >> > to
> >> go
> >> > to a particular previous page.
> >> >
> >> > Warm Regards,
> >> > Tariq
> >> > https://mtariq.jux.com/
> >> > cloudfront.blogspot.com
> >> >
> >> >
> >> > On Fri, Jan 25, 2013 at 10:28 AM, Vijay Ganesan <[EMAIL PROTECTED]>
> >> > wrote:
> >> >
> >> >> I'm displaying rows of data from a HBase table in a data grid UI. The
> >> >> grid
> >> >> shows 25 rows at a time i.e. it is paginated. User can click on
> >> >> Next/Previous to paginate through the data 25 rows at a time. I can
> >> >> implement Next easily by setting a HBase
> >> >> org.apache.hadoop.hbase.filter.PageFilter and setting startRow on the

Thanks & Regards,
Anil Gupta