Use value-based LRU cache in NodeHash

lucene/core/src/java/org/apache/lucene/util/ByteBlockPool.java

@@ -38,6 +38,8 @@ public final class ByteBlockPool implements Accountable {
 
   /** Abstract class for allocating and freeing byte blocks. */
   public abstract static class Allocator {
+    // TODO: ByteBlockPool assume the blockSize is always {@link BYTE_BLOCK_SIZE}, but this class
+    // allow arbitrary value of blockSize. We should make them consistent.
     protected final int blockSize;
 
     protected Allocator(int blockSize) {
@@ -215,19 +217,38 @@ void setBytesRef(BytesRefBuilder builder, BytesRef result, long offset, int leng
 
   /** Appends the bytes in the provided {@link BytesRef} at the current position. */
   public void append(final BytesRef bytes) {
-    int bytesLeft = bytes.length;
-    int offset = bytes.offset;
+    append(bytes.bytes, bytes.offset, bytes.length);
+  }
+
+  /**
+   * Append the provided byte array at the current position.
+   *
+   * @param bytes the byte array to write
+   */
+  public void append(final byte[] bytes) {
+    append(bytes, 0, bytes.length);
+  }
+
+  /**
+   * Append some portion of the provided byte array at the current position.
+   *
+   * @param bytes the byte array to write
+   * @param offset the offset of the byte array
+   * @param length the number of bytes to write
+   */
+  public void append(final byte[] bytes, int offset, int length) {
+    int bytesLeft = length;
     while (bytesLeft > 0) {
       int bufferLeft = BYTE_BLOCK_SIZE - byteUpto;
       if (bytesLeft < bufferLeft) {
         // fits within current buffer
-        System.arraycopy(bytes.bytes, offset, buffer, byteUpto, bytesLeft);
+        System.arraycopy(bytes, offset, buffer, byteUpto, bytesLeft);
         byteUpto += bytesLeft;
         break;
       } else {
         // fill up this buffer and move to next one
         if (bufferLeft > 0) {
-          System.arraycopy(bytes.bytes, offset, buffer, byteUpto, bufferLeft);
+          System.arraycopy(bytes, offset, buffer, byteUpto, bufferLeft);
         }
         nextBuffer();
         bytesLeft -= bufferLeft;
@@ -256,6 +277,18 @@ public void readBytes(final long offset, final byte[] bytes, int bytesOffset, in
     }
   }
 
+  /**
+   * Read a single byte at the given offset
+   *
+   * @param offset the offset to read
+   * @return the byte
+   */
+  public byte readByte(final long offset) {
+    int bufferIndex = (int) (offset >> BYTE_BLOCK_SHIFT);
+    int pos = (int) (offset & BYTE_BLOCK_MASK);
+    return buffers[bufferIndex][pos];
+  }
+
   @Override
   public long ramBytesUsed() {
     long size = BASE_RAM_BYTES;
@@ -269,4 +302,9 @@ public long ramBytesUsed() {
     }
     return size;
   }
+
+  /** the current position (in absolute value) of this byte pool */
+  public long getPosition() {
+    return bufferUpto * allocator.blockSize + byteUpto;
+  }
 }

lucene/core/src/java/org/apache/lucene/util/fst/ByteBlockPoolReverseBytesReader.java

@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.util.fst;
+
+import java.io.IOException;
+import org.apache.lucene.util.ByteBlockPool;
+
+/** Reads in reverse from a ByteBlockPool. */
+final class ByteBlockPoolReverseBytesReader extends FST.BytesReader {
+
+  private final ByteBlockPool buf;
+  // the difference between the FST node address and the hash table copied node address
+  private long posDelta;
+  private long pos;
+
+  public ByteBlockPoolReverseBytesReader(ByteBlockPool buf) {
+    this.buf = buf;
+  }
+
+  @Override
+  public byte readByte() {
+    return buf.readByte(pos--);
+  }
+
+  @Override
+  public void readBytes(byte[] b, int offset, int len) {
+    for (int i = 0; i < len; i++) {
+      b[offset + i] = buf.readByte(pos--);
+    }
+  }
+
+  @Override
+  public void skipBytes(long numBytes) throws IOException {
+    pos -= numBytes;
+  }
+
+  @Override
+  public long getPosition() {
+    return pos + posDelta;
+  }
+
+  @Override
+  public void setPosition(long pos) {
+    this.pos = pos - posDelta;
+  }
+
+  @Override
+  public boolean reversed() {
+    return true;
+  }
+
+  public void setPosDelta(long posDelta) {
+    this.posDelta = posDelta;
+  }
+}

lucene/core/src/java/org/apache/lucene/util/fst/BytesStore.java

@@ -444,11 +444,7 @@ public boolean reversed() {
 
   @Override
   public FST.BytesReader getReverseBytesReader() {
-    return getReverseReader(true);
-  }
-
-  FST.BytesReader getReverseReader(boolean allowSingle) {
-    if (allowSingle && blocks.size() == 1) {
+    if (blocks.size() == 1) {
       return new ReverseBytesReader(blocks.get(0));
     }
     return new FST.BytesReader() {

lucene/core/src/java/org/apache/lucene/util/fst/FSTCompiler.java

@@ -145,7 +145,7 @@ private FSTCompiler(
     if (suffixRAMLimitMB < 0) {
       throw new IllegalArgumentException("ramLimitMB must be >= 0; got: " + suffixRAMLimitMB);
     } else if (suffixRAMLimitMB > 0) {
-      dedupHash = new NodeHash<>(this, suffixRAMLimitMB, bytes.getReverseReader(false));
+      dedupHash = new NodeHash<>(this, suffixRAMLimitMB);
     } else {
       dedupHash = null;
     }