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HBase, mail # user - Slow scanning for PrefixFilter on EncodedBlocks


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Re: Slow scanning for PrefixFilter on EncodedBlocks
anil gupta 2012-10-17, 19:25
Hi Lars,

There is a specific use case for this:

Table: Suppose i have a rowkey:<customer_id><event_timestamp><uid>

Use case: I would like to get all the events of customer_id=123.
Case 1: If i only use startRow=123 then i will get events of  other
customers having customers_id > 123 since the scanner will be keep on
fetching rows until the end of table.
Case 2: If i use prefixFilter=123 and startRow=123 then i will get the
correct result.

IMHO, adding the feature of smartly adding the startRow in PrefixFilter
wont hurt any existing functionality. Use of StartRow and PrefixFilter will
still be different.

Thanks,
Anil Gupta
On Wed, Oct 17, 2012 at 1:11 PM, lars hofhansl <[EMAIL PROTECTED]> wrote:

> That is a good point. There is no reason why prefix filter cannot issue a
> seek to the first KV for that prefix.
> Although it lead to a practice where people would the prefix filter when
> they in fact should just set the start row.
>
>
>
>
> ----- Original Message -----
> From: anil gupta <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> Cc:
> Sent: Wednesday, October 17, 2012 9:41 AM
> Subject: Re: Slow scanning for PrefixFilter on EncodedBlocks
>
> Hi Zahoor,
>
> I heavily use prefix filter. Every time i have to explicitly define the
> startRow. So, that's the current behavior. However, initially this behavior
> was confusing to me also.
> I think that when a Prefix filter is defined then internally the
> startRow=prefix can be set. User defined StartRow takes precedence over the
> prefixFilter startRow. If the current prefixFilter can be modified in that
> way then it will eradicate this confusion regarding performance of prefix
> filter.
>
> Thanks,
> Anil Gupta
>
> On Wed, Oct 17, 2012 at 3:44 AM, J Mohamed Zahoor <[EMAIL PROTECTED]>
> wrote:
>
> > First i upgraded my cluster to 94.2.. even then the problem persisted..
> > Then i moved to using startRow instead of prefix filter..
> >
> >
> > ,/zahoor
> >
> > On Wed, Oct 17, 2012 at 2:12 PM, J Mohamed Zahoor <[EMAIL PROTECTED]>
> > wrote:
> >
> > > Sorry for the delay.
> > >
> > > It looks like the problem is because of PrefixFilter...
> > > I assumed that i does a seek...
> > >
> > > If i use startRow instead.. it works fine.. But is it the correct
> > approach?
> > >
> > > ./zahoor
> > >
> > >
> > > On Wed, Oct 17, 2012 at 3:38 AM, lars hofhansl <[EMAIL PROTECTED]
> > >wrote:
> > >
> > >> I reopened HBASE-6577
> > >>
> > >>
> > >>
> > >> ----- Original Message -----
> > >> From: lars hofhansl <[EMAIL PROTECTED]>
> > >> To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>; lars hofhansl <
> > >> [EMAIL PROTECTED]>
> > >> Cc:
> > >> Sent: Tuesday, October 16, 2012 2:39 PM
> > >> Subject: Re: Slow scanning for PrefixFilter on EncodedBlocks
> > >>
> > >> Looks like this is exactly the scenario I was trying to optimize with
> > >> HBASE-6577. Hmm...
> > >> ________________________________
> > >> From: lars hofhansl <[EMAIL PROTECTED]>
> > >> To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
> > >> Sent: Tuesday, October 16, 2012 12:21 AM
> > >> Subject: Re: Slow scanning for PrefixFilter on EncodedBlocks
> > >>
> > >> PrefixFilter does not do any seeking by itself, so I doubt this is
> > >> related to HBASE-6757.
> > >> Does this only happen with FAST_DIFF compression?
> > >>
> > >>
> > >> If you can create an isolated test program (that sets up the scenario
> > and
> > >> then runs a scan with the filter such that it is very slow), I'm happy
> > to
> > >> take a look.
> > >>
> > >> -- Lars
> > >>
> > >>
> > >>
> > >> ----- Original Message -----
> > >> From: J Mohamed Zahoor <[EMAIL PROTECTED]>
> > >> To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
> > >> Cc:
> > >> Sent: Monday, October 15, 2012 10:27 AM
> > >> Subject: Re: Slow scanning for PrefixFilter on EncodedBlocks
> > >>
> > >> Is this related to HBASE-6757 ?
> > >> I use a filter list with
> > >>   - prefix filter
> > >>   - filter list of column filters
> > >>
> > >> /zahoor
> > >>
> > >> On Monday, October 15, 2012, J Mohamed Zahoor wrote:
Thanks & Regards,
Anil Gupta