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  • hbase

    http://grokbase.com/t/hbase/user/125ya2cxxs/scan-addfamily-vs-familyfilter-equal

    http://stackoverflow.com/questions/7256100/scan-with-filter-using-hbase-shell

    Just to add on.
    The java doc clearly says in FamilyFilter that

    * If an already known column family is looked for, use {@link
    org.apache.hadoop.hbase.client.Get#addFamily(byte[])}
    * directly rather than a filter.

    So addFamily should be better.

    Regards
    Ram

    -----Original Message-----
    From: Anoop Sam John
    Sent: Thursday, May 31, 2012 11:49 AM
    To: user@hbase.apache.org
    Subject: RE: Scan addFamily vs FamilyFilter(EQUAL, ...)

    Hi,
    As per my understanding of the Scan code in your scenario where
    you want to go with scanning of some CFs ( not all) You go with
    Scan#addFamily.
    The FamilyFilter also doing the same thing. But there is a difference
    in the performance.
    When one specify the CFs in the scan, the scanner will be created for
    only those many Stores. For the other CFs, there wont be any scanners
    and so those stores are not scanned. ( The HFile data is not fetched )
    Instead when one use the FamilyFilter and not specify any specific
    columns (using Scan#addFamily) all the stores will get scanned and data
    will get fetched from HFiles. Later these KVs corresponding to which
    you needed (as per your FamilyFilter) only will get included in the
    Result and others just avoided. So there will be performance
    difference I feel.. Correct me if I am wrong pls...

    @Stack
    One thing I ran into when using the Scan.addFamily / Scan.addColumn is
    that those two methods overwrite each other.
    In the Scan#addColumn javadoc it is clearly telling about this
    overwrites... So this seems intentionally done correct?


    -Anoop-
    ________________________________________
    From: saint.ack@gmail.com [saint.ack@gmail.com] on behalf of Stack
    [stack@duboce.net]
    Sent: Wednesday, May 30, 2012 11:13 PM
    To: user@hbase.apache.org
    Subject: Re: Scan addFamily vs FamilyFilter(EQUAL, ...)
    On Wed, May 30, 2012 at 9:59 AM, Kevin wrote:
    I am curious and trying to learn which method is best when wanting to limit
    a scan to a particular column or column family. The Scan class carries a
    Filter instance and a TreeMap of the family map and I am unsure how they
    get carried through to the server-side functionality. In terms of
    performance is there any difference between doing Scan.addFamily(x) and
    Scan.setFilter(new FamilyFilter(CompareFilter.CompareOp.EQUAL, x)?
    There is probably not noticeable difference in performance but
    Scan#addFamily is the more natural way of expressing column family
    scoping.
    St.Ack
     
     
     
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  • 原文地址:https://www.cnblogs.com/jvava/p/4580956.html
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