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Date: Fri, 17 Feb 2012 11:30:24 -0800
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 <CAPud8TqeV76maHDpWSkqwhrwk_KUitV6TdOcyBa4p=UZ=HKW_Q@mail.gmail.com>
Subject: Re: How to define a custom filter to skip some amount of rows?
From: Dmitriy Lyubimov <dlieu.7@gmail.com>
To: user@hbase.apache.org
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Filters support re-seek functionality. Hint can be given on the point
of re-seek. Re-seek can be applied to either columns or rows
(basically, hint is the new target of re-seek as key-value). You can
find details in the hbase book (and perhaps somewhere online, too).

-d

On Mon, Feb 13, 2012 at 5:27 PM, NNever <nneverwei@gmail.com> wrote:
> Hello~
> In HBase-0.92.0rc4.
> If I need to skip some amount of rows from the scan result, how can I
> define a custom filter to do it?
> Here is my solution:
>
> *public class SkipFilter extends FilterBase{*
> * =A0 =A0private long totalSkip =3D -1;*
> * =A0 =A0private long currentSkip =3D 0;*
> * =A0 =A0*
> * =A0 =A0public SkipFilter(){}*
> *
> *
> * =A0 =A0public SkipFilter(long totalSkip){*
> * =A0 =A0 =A0 =A0this.totalSkip =3D totalSkip;*
> * =A0 =A0 =A0 =A0currentSkip =3D 0;*
> * =A0 =A0}*
> *
> *
> * =A0 =A0// Only override this method*
> * =A0 =A0public boolean filterRowKey(byte[] buffer, int offset, int lengt=
h){*
> * =A0 =A0 =A0 =A0if(currentSkip < totalSkip){*
> * =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0currentSkip++;*
> * =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return true;*
> * =A0 =A0 =A0 =A0}else{*
> * =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return false;*
> * =A0 =A0 =A0 =A0}*
> * =A0 =A0}*
> *
> *
> * =A0 =A0...readFileds...*
> * =A0 =A0...write...*
> *}*
>
> And used like this:
>
> *Scan scan =3D new Scan();*
> *scan.setStartRow(xxx);*
> *scan.setEndRow(xxx);*
> *Filter someFilter =3D new XXXFilter();*
> *Filter skipFilter =3D new SkipFilter(100);*
> *scan.setFilter(new FilterList(someFilter,...,skipFilter));*
> *...doScan....*
>
> *
> *
> Well, it works fine. =A0I scan some table, and the result can jump the fi=
rst
> 100 rows, start from the 101th suitable row.
> But when I delete some row from this table, tragedy accure!! *The
> filter.filterRowKey can meet the deleted row*(I have post a mail before t=
o
> discribe this).
> So if I try to skip the first 100 undeleted row, I user SkipFilter(100),
> but infact it can only filter out 99 rows.
> If I use this to do Paging, then at the second page I may meet the same r=
ow
> from first page.
>
> Can someone give me some suggestions on it or how to design a better
> SkipFilter to suit my need?
> Thanks!