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Date: Tue, 18 Feb 2014 19:46:36 +0000 (UTC)
From: "Edward Capriolo (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12695127.1392342085207.59355.1392752796299@arcas>
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Subject: [jira] [Commented] (CASSANDRA-6704) Create wide row scanners
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    [ https://issues.apache.org/jira/browse/CASSANDRA-6704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13904480#comment-13904480 ] 

Edward Capriolo commented on CASSANDRA-6704:
--------------------------------------------

But I see no reason why a query language could not use a scanner to help it answer a query. Potentially paging the results of N scans at once or something like that.

> Create wide row scanners
> ------------------------
>
>                 Key: CASSANDRA-6704
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6704
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Edward Capriolo
>            Assignee: Edward Capriolo
>
> The BigTable white paper demonstrates the use of scanners to iterate over rows and columns. http://static.googleusercontent.com/media/research.google.com/en/us/archive/bigtable-osdi06.pdf
> Because Cassandra does not have a primary sorting on row keys scanning over ranges of row keys is less useful. 
> However we can use the scanner concept to operate on wide rows. For example many times a user wishes to do some custom processing inside a row and does not wish to carry the data across the network to do this processing. 
> I have already implemented thrift methods to compile dynamic groovy code into Filters as well as some code that uses a Filter to page through and process data on the server side.
> https://github.com/edwardcapriolo/cassandra/compare/apache:trunk...trunk
> The following is a working code snippet.
> {code}
>     @Test
>     public void test_scanner() throws Exception
>     {
>       ColumnParent cp = new ColumnParent();
>       cp.setColumn_family("Standard1");
>       ByteBuffer key = ByteBuffer.wrap("rscannerkey".getBytes());
>       for (char a='a'; a < 'g'; a++){
>         Column c1 = new Column();
>         c1.setName((a+"").getBytes());
>         c1.setValue(new byte [0]);
>         c1.setTimestamp(System.nanoTime());
>         server.insert(key, cp, c1, ConsistencyLevel.ONE);
>       }
>       
>       FilterDesc d = new FilterDesc();
>       d.setSpec("GROOVY_CLASS_LOADER");
>       d.setName("limit3");
>       d.setCode("import org.apache.cassandra.dht.* \n" +
>               "import org.apache.cassandra.thrift.* \n" +
>           "public class Limit3 implements SFilter { \n " +
>           "public FilterReturn filter(ColumnOrSuperColumn col, List<ColumnOrSuperColumn> filtered) {\n"+
>           " filtered.add(col);\n"+
>           " return filtered.size()< 3 ? FilterReturn.FILTER_MORE : FilterReturn.FILTER_DONE;\n"+
>           "} \n" +
>         "}\n");
>       server.create_filter(d);
>       
>       
>       ScannerResult res = server.create_scanner("Standard1", "limit3", key, ByteBuffer.wrap("a".getBytes()));
>       Assert.assertEquals(3, res.results.size());
>     }
> {code}
> I am going to be working on this code over the next few weeks but I wanted to get the concept our early so the design can see some criticism.


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