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From "HBase Review Board (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2794) ROWCOL bloom filter not used if multiple columns within same family are requested in a Get
Date Mon, 12 Jul 2010 17:21:53 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12887433#action_12887433
] 

HBase Review Board commented on HBASE-2794:
-------------------------------------------

Message from: "Nicolas" <nspiegelberg@facebook.com>

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This is an automatically generated e-mail. To reply, visit:
http://review.hbase.org/r/296/#review350
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/trunk/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFile.java
<http://review.hbase.org/r/296/#comment1468>

    have you done any tests to see when the number of bloom checks takes significant time
compared to just getting the block?  For example, if you have 100 columns to lookup, do bloom
filters really buy you anything, or shouldn't you just switch to a Row-level bloom anyways?
 Also, with a default 1% error rate, you're looking at ~100% false positive with 100 columns.
 Maybe max.columns = sqrt(1/error.rate)



/trunk/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFile.java
<http://review.hbase.org/r/296/#comment1463>

    probably should pre-allocate the ArrayList() size so we only deal with one heap element.


- Nicolas





> ROWCOL bloom filter not used if multiple columns within same family are requested in
a Get
> ------------------------------------------------------------------------------------------
>
>                 Key: HBASE-2794
>                 URL: https://issues.apache.org/jira/browse/HBASE-2794
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Kannan Muthukkaruppan
>         Attachments: 2794_multi_column_check.txt
>
>
> Noticed the following snippet in StoreFile.java:Scanner:shouldSeek():
> {code}
>         switch(bloomFilterType) {
>           case ROW:
>             key = row;
>             break;
>           case ROWCOL:
>             if (columns.size() == 1) {
>               byte[] col = columns.first();
>               key = Bytes.add(row, col);
>               break;
>             }
>             //$FALL-THROUGH$
>           default:
>             return true;
>         }
> {code}
> If columns.size > 1, then we currently don't take advantage of the bloom filter. 
We should optimize this to check bloom for each of columns and if none of the columns are
present in the bloom avoid opening the file.

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