Prefix search implementation

Implemente a solution to the issue described by google/leveldb#610
pcmind · Nov 26, 2018 · da3771e · da3771e
1 parent a302df6
commit da3771e
Show file tree

Hide file tree

Showing 4 changed files with 41 additions and 2 deletions.
diff --git a/leveldb-api/src/main/java/org/iq80/leveldb/DB.java b/leveldb-api/src/main/java/org/iq80/leveldb/DB.java
@@ -35,6 +35,11 @@ byte[] get(byte[] key, ReadOptions options)
     @Override
     DBIterator iterator();
 
+    default DBIterator prefixIterator(ReadOptions options, byte[] prefix)
+    {
+        throw new UnsupportedOperationException();
+    }
+
     DBIterator iterator(ReadOptions options);
 
     void put(byte[] key, byte[] value)

diff --git a/leveldb/src/main/java/org/iq80/leveldb/impl/DbImpl.java b/leveldb/src/main/java/org/iq80/leveldb/impl/DbImpl.java
@@ -971,14 +971,20 @@ public SeekingIteratorAdapter iterator()
 
     @Override
     public SeekingIteratorAdapter iterator(ReadOptions options)
+    {
+        return prefixIterator(options, null);
+    }
+
+    @Override
+    public SeekingIteratorAdapter prefixIterator(ReadOptions options, byte[] prefix)
     {
         mutex.lock();
         try {
             DbIterator rawIterator = internalIterator(options);
 
             // filter out any entries not visible in our snapshot
             long snapshot = getSnapshot(options);
-            SnapshotSeekingIterator snapshotIterator = new SnapshotSeekingIterator(rawIterator, snapshot, internalKeyComparator.getUserComparator(), new Random(), this);
+            SnapshotSeekingIterator snapshotIterator = new SnapshotSeekingIterator(rawIterator, snapshot, internalKeyComparator.getUserComparator(), prefix == null || prefix.length == 0 ? null : Slices.wrappedBuffer(prefix), new Random(), this);
             return new SeekingIteratorAdapter(snapshotIterator);
         }
         finally {

diff --git a/leveldb/src/main/java/org/iq80/leveldb/impl/SnapshotSeekingIterator.java b/leveldb/src/main/java/org/iq80/leveldb/impl/SnapshotSeekingIterator.java
@@ -36,12 +36,14 @@ public final class SnapshotSeekingIterator
     private final Random r;
     private final DbImpl db;
     private int bytesCounter;
+    private final Slice prefix;
 
-    public SnapshotSeekingIterator(DbIterator iterator, long sequence, Comparator<Slice> userComparator, Random r, DbImpl db)
+    public SnapshotSeekingIterator(DbIterator iterator, long sequence, Comparator<Slice> userComparator, Slice prefix, Random r, DbImpl db)
     {
         this.iterator = iterator;
         this.sequence = sequence;
         this.userComparator = userComparator;
+        this.prefix = prefix;
         this.r = r;
         this.db = db;
         this.bytesCounter = getRandomPeriod(); //use this.r
@@ -105,6 +107,9 @@ private void findNextUserEntry()
             if (key.getSequenceNumber() > sequence) {
                 continue;
             }
+            if (prefix != null && !prefix.isPrefixOf(key.getUserKey())) {
+                break;
+            }
             if (key.getValueType() == ValueType.DELETION) {
                 while (iterator.hasNext()) {
                     Entry<InternalKey, Slice> peek = iterator.peek();

diff --git a/leveldb/src/main/java/org/iq80/leveldb/util/Slice.java b/leveldb/src/main/java/org/iq80/leveldb/util/Slice.java
@@ -681,6 +681,29 @@ public int compareTo(Slice that)
         return this.length - that.length;
     }
 
+    public boolean isPrefixOf(Slice that)
+    {
+        if (this == that) {
+            return true;
+        }
+        if (this.data == that.data && length == that.length && offset == that.offset) {
+            return true;
+        }
+        if (this.length > that.length) {
+            return false;
+        }
+
+        int minLength = this.length;
+        for (int i = 0; i < minLength; i++) {
+            int thisByte = 0xFF & this.data[this.offset + i];
+            int thatByte = 0xFF & that.data[that.offset + i];
+            if (thisByte != thatByte) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     /**
      * Decodes this buffer's readable bytes into a string with the specified
      * character set name.