Mailing-List: contact hbase-dev-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: hbase-dev@hadoop.apache.org
Received-SPF: pass (athena.apache.org: domain of jlist@streamy.com designates
 72.34.249.3 as permitted sender)
Message-ID: <4A8DA731.9030408@streamy.com>
Date: Thu, 20 Aug 2009 12:42:41 -0700
From: Jonathan Gray <jlist@streamy.com>
User-Agent: Thunderbird 2.0.0.22 (Windows/20090605)
MIME-Version: 1.0
To: hbase-dev@hadoop.apache.org
Subject: Re: real prefix filter
References: <4A8D43DD.6060103@b-ideas.eu> <4A8D6CF4.7080703@streamy.com>
 <78568af10908201150o7773ef5bl971d6c385e449587@mail.gmail.com>
In-Reply-To: <78568af10908201150o7773ef5bl971d6c385e449587@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Thanks Ryan.

Do note, this will not give you proper behavior on a Get, only a Scan. 
I don't just mean the prefix+while, I also mean using the 
WhileMatchFilter at all on a Get.

Filters are allowed in Gets because you can filter on columns and values 
as well, they don't make sense on row keys.  If you need an "early-out" 
filter with a Get, you most likely need to use a Scan instead.

This kind of confusion/inconsistency is more reason to re-implement Gets 
as optimized Scans...

JG

Ryan Rawson wrote:
> The expected idiom is like so:
>       scanSpec.setFilter(new WhileMatchFilter(
>           new PrefixFilter(prefix)));
> 
> This is common for most filters, rather than encoding the 'stop once
> past' type of logic, it is embedded in the while match flter and all
> others are wrapped with it where necessary.
> 
> -ryan
> 
> 2009/8/20 Jonathan Gray <jlist@streamy.com>:
>> It should, perhaps, stop once you pass the prefix.  I actually thought it
>> did, but you and the code say otherwise.  Doing the early-out with a Get is
>> actually not possible, so this may be why it is not implemented as such.
>>
>> However, a Scan can take both a startRow and a stopRow.  So you can use that
>> to early-out instead.
>>
>> Given that filters now work with Gets, you cannot actually implement the
>> early-out within the filter.  You'll have to use start/stop rows.  One could
>> argue a prefix filter may not make much sense on a Get (since you must
>> explicitly specify row), so if you'd like to raise that issue and see if we
>> could integrate an early-out in the filter, please file a JIRA.
>>
>> JG
>>
>> Matus Zamborsky wrote:
>>> Hello,
>>> I am scaning hbase a table with Scan and I am using PrefixFilter. As I
>>> understand, it scans the whole table and run the filter on every row. But
>>> why it does not stop after finding row without the desired prefix? If it did
>>> not find the prefix, if should return true in filterAllRemaining calling.
>>> Combining this with possible specifing the start row in Scan object, one
>>> can very fast filter only rows with the desired prefix.
>>>
>>> I am using hbase 0.20 from trunk.
>>>
>>> Regards
>>>
>>> Matus Zamborsky
>>>
>