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From Anoop Sam John <anoo...@huawei.com>
Subject RE: Pagination with HBase - getting previous page of data
Date Wed, 30 Jan 2013 11:31:49 GMT
@Anil

>I could not understand that why it goes to multiple regionservers in
parallel. Why it cannot guarantee results <= page size( my guess: due to
multiple RS scans)? If you have used it then maybe you can explain the
behaviour?

Scan from client side never go to multiple RS in parallel. Scan from HTable API will be sequential
with one region after the other. For every region it will open up scanner in the RS and do
next() calls. The filter will be instantiated at server side per region level ...

When u need 100 rows in the page and you created a Scan at client side with the filter and
suppose there are 2 regions, 1st the scanner is opened at for region1 and scan is happening.
It will ensure that max 100 rows will be retrieved from that region.  But when the region
boundary crosses and client automatically open up scanner for the region2, there also it will
pass filter with max 100 rows and so from there also max 100 rows can come..  So over all
at the client side we can not guartee that the scan created will only scan 100 rows as a whole
from the table.

I think I am making it clear.   I have not PageFilter at all.. I am just explaining as per
the knowledge on scan flow and the general filter usage.

"This is because the filter is applied separately on different region servers. It does however
optimize the scan of individual HRegions by making sure that the page size is never exceeded
locally. "

I guess it need to be saying that   "This is because the filter is applied separately on different
regions".

-Anoop-

________________________________________
From: anil gupta [anilgupta84@gmail.com]
Sent: Wednesday, January 30, 2013 1:33 PM
To: user@hbase.apache.org
Subject: Re: Pagination with HBase - getting previous page of data

Hi Mohammad,

You are most welcome to join the discussion. I have never used PageFilter
so i don't really have concrete input.
I had a look at
http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/filter/PageFilter.html
I could not understand that why it goes to multiple regionservers in
parallel. Why it cannot guarantee results <= page size( my guess: due to
multiple RS scans)? If you have used it then maybe you can explain the
behaviour?

Thanks,
Anil

On Tue, Jan 29, 2013 at 7:32 PM, Mohammad Tariq <dontariq@gmail.com> wrote:

> I'm kinda hesitant to put my leg in between the pros ;)But, does it sound
> sane to use PageFilter for both rows and columns and having some additional
> logic to handle the 'nth' page logic?It'll help us in both kind of paging.
>
> On Wednesday, January 30, 2013, Jean-Marc Spaggiari <
> jean-marc@spaggiari.org>
> wrote:
> > Hi Anil,
> >
> > I think it really depend on the way you want to use the pagination.
> >
> > Do you need to be able to jump to page X? Are you ok if you miss a
> > line or 2? Is your data growing fastly? Or slowly? Is it ok if your
> > page indexes are a day old? Do you need to paginate over 300 colums?
> > Or just 1? Do you need to always have the exact same number of entries
> > in each page?
> >
> > For my usecase I need to be able to jump to the page X and I don't
> > have any content. I have hundred of millions lines. Only the rowkey
> > matter for me and I'm fine if sometime I have 50 entries displayed,
> > and sometime only 45. So I'm thinking about calculating which row is
> > the first one for each page, and store that separatly. Then I just
> > need to run the MR daily.
> >
> > It's not a perfect solution I agree, but this might do the job for me.
> > I'm totally open to all other idea which might do the job to.
> >
> > JM
> >
> > 2013/1/29, anil gupta <anilgupta84@gmail.com>:
> >> Yes, your suggested solution only works on RowKey based pagination. It
> will
> >> fail when you start filtering on the basis of columns.
> >>
> >> Still, i would say it's comparatively easier to maintain this at
> >> Application level rather than creating tables for pagination.
> >>
> >> What if you have 300 columns in your schema. Will you create 300 tables?
> >> What about handling of pagination when filtering is done based on
> multiple
> >> columns ("and" and "or" conditions)?
> >>
> >> On Tue, Jan 29, 2013 at 1:08 PM, Jean-Marc Spaggiari <
> >> jean-marc@spaggiari.org> wrote:
> >>
> >>> No, no killer solution here ;)
> >>>
> >>> But I'm still thinking about that because I might have to implement
> >>> some pagination options soon...
> >>>
> >>> As you are saying, it's only working on the row-key, but if you want
> >>> to do the same-thing on non-rowkey, you might have to create a
> >>> secondary index table...
> >>>
> >>> JM
> >>>
> >>> 2013/1/27, anil gupta <anilgupta84@gmail.com>:
> >>> > That's alright..I thought that you have come-up with a killer
> solution.
> >>> So,
> >>> > got curious to hear your ideas. ;)
> >>> > It seems like your below mentioned solution will not work on
> filtering
> >>> > on
> >>> > non row-key columns since when you are deciding the page numbers you
> >>> > are
> >>> > only considering rowkey.
> >>> >
> >>> > Thanks,
> >>> > Anil
> >>> >
> >>> > On Fri, Jan 25, 2013 at 6:58 PM, Jean-Marc Spaggiari <
> >>> > jean-marc@spaggiari.org> wrote:
> >>> >
> >>> >> Hi Anil,
> >>> >>
> >>> >> I don't have a solution. I never tought about that ;) But I was
> >>> >> thinking about something like you create a 2nd table where you
place
> >>> >> the raw number (4 bytes) then the raw key. You go directly to a
> >>> >> specific page, you query by the number, found the key, and you
know
> >>> >> where to start you scan in the main table.
> >>> >>
> >>> >> The issue is properly the number for each lines since with a MR
you
> >>> >> don't know where you are from the beginning. But you can built
> >>> >> something where you store the line number from the beginning of
the
> >>> >> region, then when all regions are parsed you can reconstruct the
> total
> >>> >> numbering... That should work...
> >>> >>
> >>> >> JM
> >>> >>
> >>> >> 2013/1/25, anil gupta <anilgupta84@gmail.com>:
> >>> >> > Inline...
> >>> >> >
> >>> >> > On Fri, Jan 25, 2013 at 9:17 AM, Jean-Marc Spaggiari <
> >>> >> > jean-marc@spaggiari.org> 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
> >
>
> --
> Warm Regards,
> Tariq
> https://mtariq.jux.com/
> cloudfront.blogspot.com
>



--
Thanks & Regards,
Anil Gupta
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