Add download + indexOuput#write implementation to RemoteIndexBuildStrategy

Signed-off-by: Jay Deng <jayd0104@gmail.com>

Author: jed326

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Features
 * [Remote Vector Index Build] Introduce Remote Native Index Build feature flag, settings, and initial skeleton [#2525](https://github.com/opensearch-project/k-NN/pull/2525)
 * [Remote Vector Index Build] Implement vector data upload and vector data size threshold setting [#2550](https://github.com/opensearch-project/k-NN/pull/2550)
+* [Remote Vector Index Build] Implement data download and IndexOutput write functionality [#2554](https://github.com/opensearch-project/k-NN/pull/2554)
 ### Enhancements
 ### Bug Fixes
 ### Infrastructure

src/main/java/org/opensearch/knn/index/codec/nativeindex/remote/RemoteIndexBuildStrategy.java

@@ -5,6 +5,7 @@
 
 package org.opensearch.knn.index.codec.nativeindex.remote;
 
+import com.google.common.annotations.VisibleForTesting;
 import lombok.extern.log4j.Log4j2;
 import org.apache.commons.lang.NotImplementedException;
 import org.opensearch.action.LatchedActionListener;
@@ -25,6 +26,7 @@
 import org.opensearch.knn.index.VectorDataType;
 import org.opensearch.knn.index.codec.nativeindex.NativeIndexBuildStrategy;
 import org.opensearch.knn.index.codec.nativeindex.model.BuildIndexParams;
+import org.opensearch.knn.index.store.IndexOutputWithBuffer;
 import org.opensearch.knn.index.vectorvalues.KNNVectorValues;
 import org.opensearch.repositories.RepositoriesService;
 import org.opensearch.repositories.Repository;
@@ -138,12 +140,12 @@ public void buildAndWriteIndex(BuildIndexParams indexInfo) throws IOException {
             log.debug("Submit vector build took {} ms for vector field [{}]", time_in_millis, indexInfo.getFieldName());
 
             stopWatch = new StopWatch().start();
-            awaitVectorBuild();
+            BlobPath downloadPath = awaitVectorBuild();
             time_in_millis = stopWatch.stop().totalTime().millis();
             log.debug("Await vector build took {} ms for vector field [{}]", time_in_millis, indexInfo.getFieldName());
 
             stopWatch = new StopWatch().start();
-            readFromRepository();
+            readFromRepository(downloadPath, indexInfo.getIndexOutputWithBuffer());
             time_in_millis = stopWatch.stop().totalTime().millis();
             log.debug("Repository read took {} ms for vector field [{}]", time_in_millis, indexInfo.getFieldName());
         } catch (Exception e) {
@@ -335,15 +337,22 @@ private void submitVectorBuild() {
 
     /**
      * Wait on remote vector build to complete
+     * @return BlobPath     The path from which we should perform download
      */
-    private void awaitVectorBuild() {
+    private BlobPath awaitVectorBuild() throws NotImplementedException {
         throw new NotImplementedException();
     }
 
     /**
      * Read constructed vector file from remote repository and write to IndexOutput
      */
-    private void readFromRepository() {
-        throw new NotImplementedException();
+    @VisibleForTesting
+    void readFromRepository(BlobPath downloadPath, IndexOutputWithBuffer indexOutputWithBuffer) throws IOException {
+        BlobContainer blobContainer = getRepository().blobStore().blobContainer(downloadPath.parent());
+        // TODO: We are using the sequential download API as multi-part parallel download is difficult for us to implement today and
+        // requires some changes in core. For more details, see: https://github.com/opensearch-project/k-NN/issues/2464
+        String fileName = downloadPath.toArray()[downloadPath.toArray().length - 1];
+        InputStream graphStream = blobContainer.readBlob(fileName);
+        indexOutputWithBuffer.writeFromStreamWithBuffer(graphStream);
     }
 }

src/main/java/org/opensearch/knn/index/store/IndexOutputWithBuffer.java

@@ -8,18 +8,25 @@
 import org.apache.lucene.store.IndexOutput;
 
 import java.io.IOException;
+import java.io.InputStream;
 
+/**
+ * Wrapper around {@link IndexOutput} to perform writes in a buffered manner. This class is created per flush/merge, and may be used twice if
+ * {@link org.opensearch.knn.index.codec.nativeindex.remote.RemoteIndexBuildStrategy} needs to fall back to a different build strategy.
+ */
 public class IndexOutputWithBuffer {
     // Underlying `IndexOutput` obtained from Lucene's Directory.
     private IndexOutput indexOutput;
     // Write buffer. Native engine will copy bytes into this buffer.
     // Allocating 64KB here since it show better performance in NMSLIB with the size. (We had slightly improvement in FAISS than having 4KB)
     // NMSLIB writes an adjacent list size first, then followed by serializing the list. Since we usually have more adjacent lists, having
     // 64KB to accumulate bytes as possible to reduce the times of calling `writeBytes`.
-    private byte[] buffer = new byte[64 * 1024];
+    private static final int CHUNK_SIZE = 64 * 1024;
+    private final byte[] buffer;
 
     public IndexOutputWithBuffer(IndexOutput indexOutput) {
         this.indexOutput = indexOutput;
+        this.buffer = new byte[CHUNK_SIZE];
     }
 
     // This method will be called in JNI layer which precisely knows
@@ -33,6 +40,43 @@ public void writeBytes(int length) {
         }
     }
 
+    /**
+     * Writes to the {@link IndexOutput} by buffering bytes into the existing buffer in this class.
+     *
+     * @param inputStream       The stream from which we are reading bytes to write
+     * @throws IOException
+     * @see IndexOutputWithBuffer#writeFromStreamWithBuffer(InputStream, byte[])
+     */
+    public void writeFromStreamWithBuffer(InputStream inputStream) throws IOException {
+        writeFromStreamWithBuffer(inputStream, this.buffer);
+    }
+
+    /**
+     * Writes to the {@link IndexOutput} by buffering bytes with @param outputBuffer. This method allows
+     * {@link org.opensearch.knn.index.codec.nativeindex.remote.RemoteIndexBuildStrategy} to provide a separate, larger buffer as that buffer is for buffering
+     * bytes downloaded from the repository, so it may be more performant to use a larger buffer.
+     * We do not change the size of the existing buffer in case a fallback to the existing build strategy is needed.
+     * TODO: Tune the size of the buffer used by RemoteIndexBuildStrategy based on benchmarking
+     *
+     * @param inputStream       The stream from which we are reading bytes to write
+     * @param outputBuffer      The buffer used to buffer bytes
+     * @throws IOException
+     * @see IndexOutputWithBuffer#writeFromStreamWithBuffer(InputStream)
+     */
+    public void writeFromStreamWithBuffer(InputStream inputStream, byte[] outputBuffer) throws IOException {
+        int bytesRead = 0;
+        // InputStream uses -1 indicates there are no more bytes to be read
+        while (bytesRead != -1) {
+            // Try to read CHUNK_SIZE into the buffer. The actual amount read may be less.
+            bytesRead = inputStream.read(outputBuffer, 0, CHUNK_SIZE);
+            assert bytesRead <= CHUNK_SIZE;
+            // However many bytes we read, write it to the IndexOutput if != -1
+            if (bytesRead != -1) {
+                indexOutput.writeBytes(outputBuffer, 0, bytesRead);
+            }
+        }
+    }
+
     @Override
     public String toString() {
         return "{indexOutput=" + indexOutput + ", len(buffer)=" + buffer.length + "}";

src/test/java/org/opensearch/knn/index/codec/nativeindex/remote/RemoteIndexBuildStrategyTests.java

@@ -12,6 +12,8 @@
 import org.apache.lucene.search.Sort;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.IOContext;
+import org.apache.lucene.store.IndexInput;
+import org.apache.lucene.store.IndexOutput;
 import org.apache.lucene.util.InfoStream;
 import org.apache.lucene.util.Version;
 import org.junit.Before;
@@ -42,11 +44,13 @@
 import org.opensearch.repositories.RepositoryMissingException;
 import org.opensearch.repositories.blobstore.BlobStoreRepository;
 
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Path;
 import java.util.List;
 import java.util.Map;
+import java.util.Random;
 
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
@@ -208,4 +212,56 @@ public void testRepositoryInteraction() throws IOException {
         verify(mockBlobStore).blobContainer(any());
         verify(mockRepository).basePath();
     }
+
+    /**
+     * Verify the buffered read method in {@link RemoteIndexBuildStrategy#readFromRepository} produces the correct result
+     */
+    public void testRepositoryRead() throws IOException {
+        // Create an InputStream with random values
+        int TEST_ARRAY_SIZE = 64 * 1024 * 10;
+        byte[] byteArray = new byte[TEST_ARRAY_SIZE];
+        Random random = new Random();
+        random.nextBytes(byteArray);
+        InputStream randomStream = new ByteArrayInputStream(byteArray);
+
+        // Create a test segment that we will read/write from
+        Directory directory;
+        directory = newFSDirectory(createTempDir());
+        String TEST_SEGMENT_NAME = "test-segment-name";
+        IndexOutput testIndexOutput = directory.createOutput(TEST_SEGMENT_NAME, IOContext.DEFAULT);
+        IndexOutputWithBuffer testIndexOutputWithBuffer = new IndexOutputWithBuffer(testIndexOutput);
+
+        // Set up RemoteIndexBuildStrategy and write to IndexOutput
+        RepositoriesService repositoriesService = mock(RepositoriesService.class);
+        BlobStoreRepository mockRepository = mock(BlobStoreRepository.class);
+        BlobPath testBasePath = new BlobPath().add("testBasePath");
+        BlobStore mockBlobStore = mock(BlobStore.class);
+        AsyncMultiStreamBlobContainer mockBlobContainer = mock(AsyncMultiStreamBlobContainer.class);
+
+        when(repositoriesService.repository(any())).thenReturn(mockRepository);
+        when(mockRepository.basePath()).thenReturn(testBasePath);
+        when(mockRepository.blobStore()).thenReturn(mockBlobStore);
+        when(mockBlobStore.blobContainer(any())).thenReturn(mockBlobContainer);
+        when(mockBlobContainer.readBlob("testFile")).thenReturn(randomStream);
+
+        RemoteIndexBuildStrategy objectUnderTest = new RemoteIndexBuildStrategy(
+            () -> repositoriesService,
+            mock(NativeIndexBuildStrategy.class),
+            mock(IndexSettings.class)
+        );
+        // This should read from randomStream into testIndexOutput
+        BlobPath testPath = new BlobPath().add("testBasePath").add("testDirectory").add("testFile");
+        objectUnderTest.readFromRepository(testPath, testIndexOutputWithBuffer);
+        testIndexOutput.close();
+
+        // Now try to read from the IndexOutput
+        IndexInput testIndexInput = directory.openInput(TEST_SEGMENT_NAME, IOContext.DEFAULT);
+        byte[] resultByteArray = new byte[TEST_ARRAY_SIZE];
+        testIndexInput.readBytes(resultByteArray, 0, TEST_ARRAY_SIZE);
+        assertArrayEquals(byteArray, resultByteArray);
+
+        // Test Cleanup
+        testIndexInput.close();
+        directory.close();
+    }
 }