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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4811) Support reverse Scan
Date Mon, 26 Aug 2013 22:34:54 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13750667#comment-13750667
] 

Ted Yu commented on HBASE-4811:
-------------------------------

In tests:
{code}
+    InternalScanner scanner = this.region.getScanner(s);
+    while (true) {
+      ArrayList<KeyValue> values = new ArrayList<KeyValue>();
+      boolean isMoreResults = scanner.next(values);
{code}
Please close the scanner at the end of the test.
{code}
+  public void testReverseScanner_FromMemStoreAndHFiles_MultiCFs1()
{code}
Can the above test be given more specific name (same for testReverseScanner_FromMemStoreAndHFiles_MultiCFs2)
?
{code}
+   * if they have the equal row, sort smaller one before than bigger one
{code}
typo: 'than' -> 'the'

In NonReversedNonLazyKeyValueScanner:
{code}
+  public boolean seekToPreviousRow(KeyValue key) throws IOException {
+    throw new NotImplementedException("seekToPreviousRow must not be called on a "
{code}
But from ReversedKeyValueHeap:
{code}
+  public boolean seekToLastRow() throws IOException {
+    throw new UnsupportedOperationException("Not implemented");
{code}
It would be nice to use the same exception for consistency.
                
> Support reverse Scan
> --------------------
>
>                 Key: HBASE-4811
>                 URL: https://issues.apache.org/jira/browse/HBASE-4811
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client
>    Affects Versions: 0.20.6, 0.94.7
>            Reporter: John Carrino
>            Assignee: Liang Xie
>             Fix For: 0.98.0
>
>         Attachments: 4811-0.94-v3.txt, 4811-trunk-v10.txt, 4811-trunk-v5.patch, HBase-4811-0.94.3modified.txt,
HBase-4811-0.94-v2.txt, hbase-4811-trunkv11.patch, hbase-4811-trunkv12.patch, hbase-4811-trunkv13.patch,
hbase-4811-trunkv14.patch, hbase-4811-trunkv15.patch, hbase-4811-trunkv16.patch, hbase-4811-trunkv17.patch,
hbase-4811-trunkv1.patch, hbase-4811-trunkv4.patch, hbase-4811-trunkv6.patch, hbase-4811-trunkv7.patch,
hbase-4811-trunkv8.patch, hbase-4811-trunkv9.patch
>
>
> All the documentation I find about HBase says that if you want forward and reverse scans
you should just build 2 tables and one be ascending and one descending.  Is there a fundamental
reason that HBase only supports forward Scan?  It seems like a lot of extra space overhead
and coding overhead (to keep them in sync) to support 2 tables.  
> I am assuming this has been discussed before, but I can't find the discussions anywhere
about it or why it would be infeasible.

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