[
https://issues.apache.org/jira/browse/HBASE-4811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13801464#comment-13801464
]
Lars Hofhansl commented on HBASE-4811:
--------------------------------------
Thanks JM! Lemme do one more test on my work machine (many cores and lots of
RAM), will report back tomorrow or the day after. Then we should just commit
this sucker.
> Support reverse Scan
> --------------------
>
> Key: HBASE-4811
> URL: https://issues.apache.org/jira/browse/HBASE-4811
> Project: HBase
> Issue Type: New Feature
> Components: Client
> Affects Versions: 0.20.6, 0.94.7
> Reporter: John Carrino
> Assignee: chunhui shen
> Fix For: 0.98.0, 0.94.13, 0.96.1
>
> Attachments: 4811-0.94-v22.txt, 4811-0.94-v3.txt, 4811-trunk-v10.txt,
> 4811-trunk-v5.patch, HBase-4811-0.94.3modified.txt, hbase-4811-0.94
> v21.patch, 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-trunkv18.patch, hbase-4811-trunkv19.patch,
> hbase-4811-trunkv1.patch, hbase-4811-trunkv20.patch,
> hbase-4811-trunkv21.patch, hbase-4811-trunkv4.patch,
> hbase-4811-trunkv6.patch, hbase-4811-trunkv7.patch, hbase-4811-trunkv8.patch,
> hbase-4811-trunkv9.patch
>
>
> Reversed scan means scan the rows backward.
> And StartRow bigger than StopRow in a reversed scan.
> For example, for the following rows:
> aaa/c1:q1/value1
> aaa/c1:q2/value2
> bbb/c1:q1/value1
> bbb/c1:q2/value2
> ccc/c1:q1/value1
> ccc/c1:q2/value2
> ddd/c1:q1/value1
> ddd/c1:q2/value2
> eee/c1:q1/value1
> eee/c1:q2/value2
> you could do a reversed scan from 'ddd' to 'bbb'(exclude) like this:
> Scan scan = new Scan();
> scan.setStartRow('ddd');
> scan.setStopRow('bbb');
> scan.setReversed(true);
> for(Result result:htable.getScanner(scan)){
> System.out.println(result);
> }
> Aslo you could do the reversed scan with shell like this:
> hbase> scan 'table',{REVERSED => true,STARTROW=>'ddd', STOPROW=>'bbb'}
> And the output is:
> ddd/c1:q1/value1
> ddd/c1:q2/value2
> ccc/c1:q1/value1
> ccc/c1:q2/value2
> NOTE: when setting reversed as true for a client scan, you must set the start
> row, else will throw exception. Through {@link
> Scan#createBiggestByteArray(int)},you could get a big enough byte array as
> the start row
> 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.
--
This message was sent by Atlassian JIRA
(v6.1#6144)
