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From anil gupta <anilgupt...@gmail.com>
Subject Re: Slow scanning for PrefixFilter on EncodedBlocks
Date Wed, 17 Oct 2012 19:25:09 GMT
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 <lhofhansl@yahoo.com> 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 <anilgupta84@gmail.com>
> To: user@hbase.apache.org
> 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 <jmozah@gmail.com>
> 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 <jmozah@gmail.com>
> > 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 <lhofhansl@yahoo.com
> > >wrote:
> > >
> > >> I reopened HBASE-6577
> > >>
> > >>
> > >>
> > >> ----- Original Message -----
> > >> From: lars hofhansl <lhofhansl@yahoo.com>
> > >> To: "user@hbase.apache.org" <user@hbase.apache.org>; lars hofhansl
<
> > >> lhofhansl@yahoo.com>
> > >> 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 <lhofhansl@yahoo.com>
> > >> To: "user@hbase.apache.org" <user@hbase.apache.org>
> > >> 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 <jmozah@gmail.com>
> > >> To: "user@hbase.apache.org" <user@hbase.apache.org>
> > >> 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:
> > >>
> > >> > Hi
> > >> >
> > >> > My scanner performance is very slow when using a Prefix filter on
a
> > >> > **Encoded Column** ( encoded using FAST_DIFF on both memory and
> disk).
> > >> > I am using 94.1 hbase.
> > >> >
> > >> > jstack shows that much time is spent on seeking the row.
> > >> > Even if i give a exact row key match in the prefix filter it takes
> > about
> > >> > two minutes to return a single row.
> > >> > Running this multiple times also seems to be redirecting things to
> > disk
> > >> > (loadBlock).
> > >> >
> > >> >
> > >> > at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$EncodedScannerV2.loadBlockAndSeekToKey(HFileReaderV2.java:1027)
> > >> > at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.seekTo(HFileReaderV2.java:461)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.reseekTo(HFileReaderV2.java:493)
> > >> > at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseekAtOrAfter(StoreFileScanner.java:242)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:167)
> > >> > at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:54)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:521)
> > >> > - locked <0x000000059584fab8> (a
> > >> > org.apache.hadoop.hbase.regionserver.StoreScanner)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:402)
> > >> > - locked <0x000000059584fab8> (a
> > >> > org.apache.hadoop.hbase.regionserver.StoreScanner)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRow(HRegion.java:3507)
> > >> > at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:3455)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:3406)
> > >> > - locked <0x000000059589bb30> (a
> > >> > org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl)
> > >> >  at
> > >> >
> > >>
> >
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:3423)
> > >> >
> > >> > If is set the start and end row as same row in scan ... it come in
> > very
> > >> > quick.
> > >> >
> > >> > Saw this link
> > >> >
> > >>
> >
> http://search-hadoop.com/m/9f0JH1Kz24U1&subj=Re+HBase+0+94+2+SNAPSHOT+Scanning+Bug
> > >> > But it looks like things are fine in 94.1.
> > >> >
> > >> > Any pointers on why this is slow?
> > >> >
> > >> >
> > >> > Note: the row has not many columns(5 and less than a kb) and lots
of
> > >> > versions (1500+)
> > >> >
> > >> > ./zahoor
> > >> >
> > >> >
> > >> >
> > >>
> > >>
> > >
> >
>
>
>
> --
> Thanks & Regards,
> Anil Gupta
>
>


-- 
Thanks & Regards,
Anil Gupta

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