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From "James Kennedy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1531) Add RowFilter to HRegion.HScanner
Date Wed, 27 Jun 2007 20:59:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508648

James Kennedy commented on HADOOP-1531:

in relation to Hadoop-1439, i'll add a comment there.

I think i needed that RowFilter() constructor to make RPC serialization happy.  Needs to instantiate
the filter before it calls readFields().

The regexp is passed to the constructor since its a single param whereas the column criteria
is many. I suppose i could add a constructor that takes a list of col criteria.

filter subpackage is a good idea... in fact it wouldn't hurt to refactor whats there into
some other sub-packages.

is the filter == null code necessary? I thought I saw RPC code that was handling nulls. Indeed
in my testing i seem to be able to pass null filters through rpc just fine. I'll dbl check
that though.

and I'll fix the other stuff you guys mentioned.

> Add RowFilter to HRegion.HScanner
> ---------------------------------
>                 Key: HADOOP-1531
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1531
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: contrib/hbase
>    Affects Versions: 0.14.0
>            Reporter: James Kennedy
>            Assignee: James Kennedy
>         Attachments: RowFilter.patch
> I've implemented a RowFilterInterface and a RowFilter implementation.  This is passed
to the HRegion.HScanner via HClient.openScanner() though it is an entirely optional parameter.
> HScanner applies the filter in the next() call by iterating until it encounters a row
that is not filtered by the RowFilter.  The filter applies criteria based on row keys and/or
column data values.
> Null values are little tricky since the resultSet in that loop may represent nulls as
absent columns or as DELETED_BYTES.  Nevertheless null cases are taken care of by the filter
and you can for example retrieve all rows where column X = null.
> The initial RowFilter implementation is limited in several ways:
> * Equality test only with literal values. No !=, <, >, etc. No col1 == col2. This
is a straight-up byte[] comparison.
> * Multiple column criteria are treated as an implicit conjunction, no disjunction possible.
> * row key criteria is a regular expression only
> * row key criteria is independent of column criteria. No "if rowkey.matches(A)  and col1==B"
 although the interface is created to allow for that.
> But it should be easy to write an improved RowFilterInterface implementation to take
care of most of the above without having to change code elsewhere.

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