Implement reverseScan

src/main/java/org/tikv/common/KVClient.java

@@ -101,7 +101,25 @@ public List<KvPair> batchGet(BackOffer backOffer, List<ByteString> keys, long ve
    */
   public List<KvPair> scan(ByteString startKey, ByteString endKey, long version)
       throws GrpcException {
-    Iterator<KvPair> iterator = scanIterator(conf, clientBuilder, startKey, endKey, version);
+    return scan(startKey, endKey, version, false);
+  }
+
+  /**
+   * Scan key-value pairs from TiKV in range [startKey, endKey) or if reversely, [endKey, startKey)
+   *
+   * @param startKey start key, inclusive
+   * @param endKey end key, exclusive
+   * @param reverse whether to scan reversely
+   * @return list of key-value pairs in range
+   */
+  public List<KvPair> scan(ByteString startKey, ByteString endKey, long version, boolean reverse)
+      throws GrpcException {
+    Iterator<KvPair> iterator;
+    if (reverse) {
+      iterator = scanIterator(conf, clientBuilder, endKey, startKey, version, reverse);
+    } else {
+      iterator = scanIterator(conf, clientBuilder, startKey, endKey, version, reverse);
+    }
     List<KvPair> result = new ArrayList<>();
     iterator.forEachRemaining(result::add);
     return result;
@@ -115,7 +133,7 @@ public List<KvPair> scan(ByteString startKey, ByteString endKey, long version)
    * @return list of key-value pairs in range
    */
   public List<KvPair> scan(ByteString startKey, long version, int limit) throws GrpcException {
-    Iterator<KvPair> iterator = scanIterator(conf, clientBuilder, startKey, version, limit);
+    Iterator<KvPair> iterator = scanIterator(conf, clientBuilder, startKey, version, limit, false);
     List<KvPair> result = new ArrayList<>();
     iterator.forEachRemaining(result::add);
     return result;
@@ -183,16 +201,18 @@ private Iterator<KvPair> scanIterator(
       RegionStoreClientBuilder builder,
       ByteString startKey,
       ByteString endKey,
-      long version) {
-    return new ConcreteScanIterator(conf, builder, startKey, endKey, version);
+      long version,
+      boolean reverse) {
+    return new ConcreteScanIterator(conf, builder, startKey, endKey, version, reverse);
   }
 
   private Iterator<KvPair> scanIterator(
       TiConfiguration conf,
       RegionStoreClientBuilder builder,
       ByteString startKey,
       long version,
-      int limit) {
-    return new ConcreteScanIterator(conf, builder, startKey, version, limit);
+      int limit,
+      boolean reverse) {
+    return new ConcreteScanIterator(conf, builder, startKey, version, limit, reverse);
   }
 }

src/main/java/org/tikv/common/Snapshot.java

@@ -157,7 +157,24 @@ public Iterator<KvPair> scan(ByteString startKey) {
         session.getRegionStoreClientBuilder(),
         startKey,
         timestamp.getVersion(),
-        Integer.MAX_VALUE);
+        Integer.MAX_VALUE,
+        false);
+  }
+
+  /**
+   * scan all keys becofe startKey, inclusive
+   *
+   * @param startKey start of keys
+   * @return iterator of kvPair
+   */
+  public Iterator<KvPair> reverseScan(ByteString startKey) {
+    return new ConcreteScanIterator(
+        session.getConf(),
+        session.getRegionStoreClientBuilder(),
+        startKey,
+        timestamp.getVersion(),
+        Integer.MAX_VALUE,
+        true);
   }
 
   /**
@@ -173,7 +190,24 @@ public Iterator<KvPair> scanPrefix(ByteString prefix) {
         session.getRegionStoreClientBuilder(),
         prefix,
         nextPrefix,
-        timestamp.getVersion());
+        timestamp.getVersion(),
+        false);
+  }
+  /**
+   * scan all keys with prefix, reversely
+   *
+   * @param prefix prefix of keys
+   * @return iterator of kvPair
+   */
+  public Iterator<KvPair> reverseScanPrefix(ByteString prefix) {
+    ByteString nextPrefix = Key.toRawKey(prefix).nextPrefix().toByteString();
+    return new ConcreteScanIterator(
+        session.getConf(),
+        session.getRegionStoreClientBuilder(),
+        nextPrefix,
+        prefix,
+        timestamp.getVersion(),
+        true);
   }
 
   public TiConfiguration getConf() {

src/main/java/org/tikv/common/operation/iterator/ConcreteScanIterator.java

@@ -44,19 +44,21 @@ public ConcreteScanIterator(
       RegionStoreClientBuilder builder,
       ByteString startKey,
       long version,
-      int limit) {
+      int limit,
+      boolean reverse) {
     // Passing endKey as ByteString.EMPTY means that endKey is +INF by default,
-    this(conf, builder, startKey, ByteString.EMPTY, version, limit);
+    this(conf, builder, startKey, ByteString.EMPTY, version, limit, reverse);
   }
 
   public ConcreteScanIterator(
       TiConfiguration conf,
       RegionStoreClientBuilder builder,
       ByteString startKey,
       ByteString endKey,
-      long version) {
+      long version,
+      boolean reverse) {
     // Passing endKey as ByteString.EMPTY means that endKey is +INF by default,
-    this(conf, builder, startKey, endKey, version, Integer.MAX_VALUE);
+    this(conf, builder, startKey, endKey, version, Integer.MAX_VALUE, reverse);
   }
 
   private ConcreteScanIterator(
@@ -65,8 +67,9 @@ private ConcreteScanIterator(
       ByteString startKey,
       ByteString endKey,
       long version,
-      int limit) {
-    super(conf, builder, startKey, endKey, limit, false);
+      int limit,
+      boolean reverse) {
+    super(conf, builder, startKey, endKey, limit, false, reverse);
     this.version = version;
   }
 
@@ -76,7 +79,7 @@ TiRegion loadCurrentRegionToCache() throws GrpcException {
     try (RegionStoreClient client = builder.build(startKey)) {
       client.setTimeout(conf.getScanTimeout());
       BackOffer backOffer = ConcreteBackOffer.newScannerNextMaxBackOff();
-      currentCache = client.scan(backOffer, startKey, version);
+      currentCache = client.scan(backOffer, startKey, version, reverse);
       // If we get region before scan, we will use region from cache which
       // may have wrong end key. This may miss some regions that split from old region.
       // Client will get the newest region during scan. So we need to

src/main/java/org/tikv/common/operation/iterator/RawScanIterator.java

@@ -39,8 +39,9 @@ public RawScanIterator(
       ByteString endKey,
       int limit,
       boolean keyOnly,
+      boolean reverse,
       BackOffer scanBackOffer) {
-    super(conf, builder, startKey, endKey, limit, keyOnly);
+    super(conf, builder, startKey, endKey, limit, keyOnly, reverse);
 
     this.scanBackOffer = scanBackOffer;
   }
@@ -56,7 +57,7 @@ TiRegion loadCurrentRegionToCache() throws GrpcException {
           currentCache = null;
         } else {
           try {
-            currentCache = client.rawScan(backOffer, startKey, limit, keyOnly);
+            currentCache = client.rawScan(backOffer, startKey, limit, keyOnly, reverse);
             // Client will get the newest region during scan. So we need to
             // update region after scan.
             region = client.getRegion();

src/main/java/org/tikv/common/operation/iterator/ScanIterator.java

@@ -43,21 +43,24 @@ public abstract class ScanIterator implements Iterator<Kvrpcpb.KvPair> {
   protected Key endKey;
   protected boolean hasEndKey;
   protected boolean processingLastBatch = false;
+  protected boolean reverse = false;
 
   ScanIterator(
       TiConfiguration conf,
       RegionStoreClientBuilder builder,
       ByteString startKey,
       ByteString endKey,
       int limit,
-      boolean keyOnly) {
+      boolean keyOnly,
+      boolean reverse) {
     this.startKey = requireNonNull(startKey, "start key is null");
     this.endKey = Key.toRawKey(requireNonNull(endKey, "end key is null"));
     this.hasEndKey = !endKey.isEmpty();
     this.limit = limit;
     this.keyOnly = keyOnly;
     this.conf = conf;
     this.builder = builder;
+    this.reverse = reverse;
   }
 
   /**

src/main/java/org/tikv/common/region/RegionStoreClient.java

@@ -70,8 +70,7 @@
 import org.tikv.common.util.HistogramUtils;
 import org.tikv.common.util.Pair;
 import org.tikv.common.util.RangeSplitter;
-import org.tikv.kvproto.Coprocessor;
-import org.tikv.kvproto.Errorpb;
+import org.tikv.kvproto.*;
 import org.tikv.kvproto.Kvrpcpb.BatchGetRequest;
 import org.tikv.kvproto.Kvrpcpb.BatchGetResponse;
 import org.tikv.kvproto.Kvrpcpb.CommitRequest;
@@ -109,8 +108,6 @@
 import org.tikv.kvproto.Kvrpcpb.SplitRegionResponse;
 import org.tikv.kvproto.Kvrpcpb.TxnHeartBeatRequest;
 import org.tikv.kvproto.Kvrpcpb.TxnHeartBeatResponse;
-import org.tikv.kvproto.Metapb;
-import org.tikv.kvproto.TikvGrpc;
 import org.tikv.kvproto.TikvGrpc.TikvBlockingStub;
 import org.tikv.kvproto.TikvGrpc.TikvFutureStub;
 import org.tikv.txn.AbstractLockResolverClient;
@@ -336,7 +333,7 @@ private List<KvPair> handleBatchGetResponse(
   }
 
   public List<KvPair> scan(
-      BackOffer backOffer, ByteString startKey, long version, boolean keyOnly) {
+      BackOffer backOffer, ByteString startKey, long version, boolean keyOnly, boolean reverse) {
     boolean forWrite = false;
     while (true) {
       Supplier<ScanRequest> request =
@@ -348,6 +345,7 @@ public List<KvPair> scan(
                   .setStartKey(codec.encodeKey(startKey))
                   .setVersion(version)
                   .setKeyOnly(keyOnly)
+                  .setReverse(reverse)
                   .setLimit(getConf().getScanBatchSize())
                   .build();
 
@@ -417,6 +415,11 @@ public List<KvPair> scan(BackOffer backOffer, ByteString startKey, long version)
     return scan(backOffer, startKey, version, false);
   }
 
+  public List<KvPair> scan(
+      BackOffer backOffer, ByteString startKey, long version, boolean reverse) {
+    return scan(backOffer, startKey, version, false, reverse);
+  }
+
   /**
    * Prewrite batch keys
    *
@@ -1238,9 +1241,11 @@ private void handleRawBatchDelete(RawBatchDeleteResponse resp) {
    * @param backOffer BackOffer
    * @param key startKey
    * @param keyOnly true if value of KvPair is not needed
+   * @param reverse
    * @return KvPair list
    */
-  public List<KvPair> rawScan(BackOffer backOffer, ByteString key, int limit, boolean keyOnly) {
+  public List<KvPair> rawScan(
+      BackOffer backOffer, ByteString key, int limit, boolean keyOnly, boolean reverse) {
     Long clusterId = pdClient.getClusterId();
     Histogram.Timer requestTimer =
         GRPC_RAW_REQUEST_LATENCY.labels("client_grpc_raw_scan", clusterId.toString()).startTimer();
@@ -1254,6 +1259,7 @@ public List<KvPair> rawScan(BackOffer backOffer, ByteString key, int limit, bool
                 .setEndKey(range.second)
                 .setKeyOnly(keyOnly)
                 .setLimit(limit)
+                .setReverse(reverse)
                 .build();
           };
 
@@ -1271,8 +1277,9 @@ public List<KvPair> rawScan(BackOffer backOffer, ByteString key, int limit, bool
     }
   }
 
-  public List<KvPair> rawScan(BackOffer backOffer, ByteString key, boolean keyOnly) {
-    return rawScan(backOffer, key, getConf().getScanBatchSize(), keyOnly);
+  public List<KvPair> rawScan(
+      BackOffer backOffer, ByteString key, boolean keyOnly, boolean reverse) {
+    return rawScan(backOffer, key, getConf().getScanBatchSize(), keyOnly, reverse);
   }
 
   private List<KvPair> rawScanHelper(RawScanResponse resp) {

src/main/java/org/tikv/raw/RawKVClient.java

@@ -1011,7 +1011,7 @@ private Iterator<KvPair> rawScanIterator(
     if (limit > MAX_RAW_SCAN_LIMIT) {
       throw ERR_MAX_SCAN_LIMIT_EXCEEDED;
     }
-    return new RawScanIterator(conf, builder, startKey, endKey, limit, keyOnly, backOffer);
+    return new RawScanIterator(conf, builder, startKey, endKey, limit, keyOnly, false, backOffer);
   }
 
   /**

src/main/java/org/tikv/txn/KVClient.java

@@ -114,8 +114,37 @@ public List<Kvrpcpb.KvPair> batchGet(BackOffer backOffer, List<ByteString> keys,
    */
   public List<Kvrpcpb.KvPair> scan(ByteString startKey, ByteString endKey, long version)
       throws GrpcException {
+    return scan(startKey, endKey, version, false);
+  }
+  /**
+   * Scan key-value pairs from TiKV reversely in range (startKey, endKey]
+   *
+   * @param startKey start key, inclusive
+   * @param endKey end key, exclusive
+   * @return list of key-value pairs in range
+   */
+  public List<Kvrpcpb.KvPair> reverseScan(ByteString startKey, ByteString endKey, long version)
+      throws GrpcException {
+    return scan(endKey, startKey, version, true);
+  }
+
+  public List<Kvrpcpb.KvPair> scan(
+      ByteString startKey, ByteString endKey, long version, boolean reverse) throws GrpcException {
+    Iterator<Kvrpcpb.KvPair> iterator;
+    if (reverse) {
+      iterator = scanIterator(conf, clientBuilder, endKey, startKey, version, reverse);
+    } else {
+      iterator = scanIterator(conf, clientBuilder, startKey, endKey, version, reverse);
+    }
+    List<Kvrpcpb.KvPair> result = new ArrayList<>();
+    iterator.forEachRemaining(result::add);
+    return result;
+  }
+
+  public List<Kvrpcpb.KvPair> scan(ByteString startKey, long version, int limit, boolean reverse)
+      throws GrpcException {
     Iterator<Kvrpcpb.KvPair> iterator =
-        scanIterator(conf, clientBuilder, startKey, endKey, version);
+        scanIterator(conf, clientBuilder, startKey, version, limit, reverse);
     List<Kvrpcpb.KvPair> result = new ArrayList<>();
     iterator.forEachRemaining(result::add);
     return result;
@@ -130,14 +159,27 @@ public List<Kvrpcpb.KvPair> scan(ByteString startKey, ByteString endKey, long ve
    */
   public List<Kvrpcpb.KvPair> scan(ByteString startKey, long version, int limit)
       throws GrpcException {
-    Iterator<Kvrpcpb.KvPair> iterator = scanIterator(conf, clientBuilder, startKey, version, limit);
-    List<Kvrpcpb.KvPair> result = new ArrayList<>();
-    iterator.forEachRemaining(result::add);
-    return result;
+    return scan(startKey, version, limit, false);
+  }
+
+  /**
+   * Scan key-value pairs reversively from TiKV in range ('', endKey], maximum to `limit` pairs
+   *
+   * @param endKey start key, inclusive
+   * @param limit limit of kv pairs
+   * @return list of key-value pairs in range
+   */
+  public List<Kvrpcpb.KvPair> reverseScan(ByteString endKey, long version, int limit)
+      throws GrpcException {
+    return scan(endKey, version, limit, true);
   }
 
   public List<Kvrpcpb.KvPair> scan(ByteString startKey, long version) throws GrpcException {
-    return scan(startKey, version, Integer.MAX_VALUE);
+    return scan(startKey, version, Integer.MAX_VALUE, false);
+  }
+
+  public List<Kvrpcpb.KvPair> reverseScan(ByteString endKey, long version) throws GrpcException {
+    return scan(endKey, version, Integer.MAX_VALUE, true);
   }
 
   public synchronized void ingest(List<Pair<ByteString, ByteString>> list) throws GrpcException {
@@ -264,17 +306,19 @@ private Iterator<Kvrpcpb.KvPair> scanIterator(
       RegionStoreClientBuilder builder,
       ByteString startKey,
       ByteString endKey,
-      long version) {
-    return new ConcreteScanIterator(conf, builder, startKey, endKey, version);
+      long version,
+      boolean reverse) {
+    return new ConcreteScanIterator(conf, builder, startKey, endKey, version, reverse);
   }
 
   private Iterator<Kvrpcpb.KvPair> scanIterator(
       TiConfiguration conf,
       RegionStoreClientBuilder builder,
       ByteString startKey,
       long version,
-      int limit) {
-    return new ConcreteScanIterator(conf, builder, startKey, version, limit);
+      int limit,
+      boolean reverse) {
+    return new ConcreteScanIterator(conf, builder, startKey, version, limit, reverse);
   }
 
   private void doIngest(TiRegion region, List<Pair<ByteString, ByteString>> sortedList)