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https://issues.apache.org/jira/browse/HBASE-4811?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13627551#comment-13627551
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Liang Xie commented on HBASE-4811:
----------------------------------
Previous HBase-4811-0.94.3modified.txt didn't have a backward-compatibility, we
can bump a SCAN version, like HBASE-6250's style:
e.g.:
{code}
--- main/java/org/apache/hadoop/hbase/client/Scan.java (revision 88835)
+++ main/java/org/apache/hadoop/hbase/client/Scan.java (working copy)
@@ -85,6 +85,7 @@
private static final String ISOLATION_LEVEL = "_isolationlevel_";
private static final byte SCAN_VERSION = (byte)2;
+ private static final byte SCAN_REVERSED_VERSION = (byte)3;
private byte [] startRow = HConstants.EMPTY_START_ROW;
private byte [] stopRow = HConstants.EMPTY_END_ROW;
private int maxVersions = 1;
@@ -577,7 +578,7 @@
public void readFields(final DataInput in)
throws IOException {
int version = in.readByte();
- if (version > (int)SCAN_VERSION) {
+ if (version > SCAN_REVERSED_VERSION) {
throw new IOException("version not supported");
}
this.startRow = Bytes.readByteArray(in);
@@ -586,7 +587,9 @@
this.batch = in.readInt();
this.caching = in.readInt();
this.cacheBlocks = in.readBoolean();
- this.reverse = in.readBoolean();
+ if (version >= SCAN_REVERSED_VERSION) {
+ this.reverse = in.readBoolean();
+ }
if(in.readBoolean()) {
this.filter =
(Filter)createForName(Bytes.toString(Bytes.readByteArray(in)));
this.filter.readFields(in);
@@ -614,14 +617,20 @@
public void write(final DataOutput out)
throws IOException {
- out.writeByte(SCAN_VERSION);
+ if (reverse) {
+ out.writeByte(SCAN_REVERSED_VERSION);
+ } else {
+ out.writeByte(SCAN_VERSION);
+ }
Bytes.writeByteArray(out, this.startRow);
Bytes.writeByteArray(out, this.stopRow);
out.writeInt(this.maxVersions);
out.writeInt(this.batch);
out.writeInt(this.caching);
out.writeBoolean(this.cacheBlocks);
- out.writeBoolean(this.reverse);
+ if (reverse) {
+ out.writeBoolean(this.reverse);
+ }
if(this.filter == null) {
out.writeBoolean(false);
} else {
{code}
> 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
> Reporter: John Carrino
> Attachments: HBase-4811-0.94.3modified.txt
>
>
> 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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