gianm commented on code in PR #16790: URL: https://github.com/apache/druid/pull/16790#discussion_r1695648063
########## extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/shuffle/output/ChannelStageOutputReader.java: ########## @@ -0,0 +1,243 @@ +/* + * 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.druid.msq.shuffle.output; + +import com.google.common.collect.ImmutableList; +import com.google.common.primitives.Ints; +import com.google.common.util.concurrent.Futures; +import com.google.common.util.concurrent.ListenableFuture; +import com.google.errorprone.annotations.concurrent.GuardedBy; +import it.unimi.dsi.fastutil.bytes.ByteArrays; +import org.apache.druid.common.guava.FutureUtils; +import org.apache.druid.error.DruidException; +import org.apache.druid.frame.channel.ByteTracker; +import org.apache.druid.frame.channel.ReadableFrameChannel; +import org.apache.druid.frame.file.FrameFileWriter; +import org.apache.druid.java.util.common.ISE; +import org.apache.druid.msq.exec.OutputChannelMode; +import org.apache.druid.msq.kernel.controller.ControllerQueryKernelUtils; + +import java.io.ByteArrayInputStream; +import java.io.IOException; +import java.io.InputStream; +import java.nio.ByteBuffer; +import java.nio.channels.WritableByteChannel; +import java.util.ArrayDeque; +import java.util.Deque; + +/** + * Reader for {@link ReadableFrameChannel}. + * + * Because this reader returns an underlying channel directly, it must only be used when it is certain that + * only a single consumer exists, i.e., when using output mode {@link OutputChannelMode#MEMORY}. See + * {@link ControllerQueryKernelUtils#canUseMemoryOutput} for the code that ensures that there is only a single + * consumer in the in-memory case. + */ +public class ChannelStageOutputReader implements StageOutputReader +{ + enum State + { + INIT, + LOCAL, + REMOTE, + CLOSED + } + + private final ReadableFrameChannel channel; + private final FrameFileWriter writer; + + /** + * Pair of chunk size + chunk InputStream. + */ + private final Deque<byte[]> chunks = new ArrayDeque<>(); + + /** + * State of this reader. + */ + @GuardedBy("this") + private State state = State.INIT; + + /** + * Position within the overall stream. + */ + @GuardedBy("this") + private long cursor; + + /** + * Offset of the first chunk in {@link #chunks} which corresponds to {@link #cursor}. + */ + @GuardedBy("this") + private int positionWithinFirstChunk; + + /** + * Whether {@link FrameFileWriter#close()} is called on {@link #writer}. + */ + @GuardedBy("this") + private boolean didCloseWriter; + + public ChannelStageOutputReader(final ReadableFrameChannel channel) + { + this.channel = channel; + this.writer = FrameFileWriter.open(new ChunkAcceptor(), null, ByteTracker.unboundedTracker()); + } + + @Override + public synchronized ListenableFuture<InputStream> readRemotelyFrom(final long offset) + { + if (state == State.INIT) { + state = State.REMOTE; + } else if (state == State.LOCAL) { + throw new ISE("Cannot read both remotely and locally"); + } else if (state == State.CLOSED) { + throw new ISE("Closed"); + } + + if (offset < cursor) { + return Futures.immediateFailedFuture( + new ISE("Offset[%,d] no longer available, current cursor is[%,d]", offset, cursor)); + } + + while (chunks.isEmpty() || offset > cursor) { + // Fetch additional chunks if needed. + if (chunks.isEmpty()) { + if (didCloseWriter) { + if (offset == cursor) { + return Futures.immediateFuture(new ByteArrayInputStream(ByteArrays.EMPTY_ARRAY)); + } else { + throw DruidException.defensive( + "Channel finished but cursor[%,d] does not match requested offset[%,d]", + cursor, + offset + ); + } + } else if (channel.isFinished()) { + try { + writer.close(); + } + catch (IOException e) { + throw new RuntimeException(e); + } + + didCloseWriter = true; + continue; + } else if (channel.canRead()) { + try { + writer.writeFrame(channel.read(), FrameFileWriter.NO_PARTITION); + } + catch (Exception e) { + try { + writer.abort(); + } + catch (IOException e2) { + e.addSuppressed(e2); + } + + throw new RuntimeException(e); + } + } else { + return FutureUtils.transformAsync(channel.readabilityFuture(), ignored -> readRemotelyFrom(offset)); + } + } + + // Remove first chunk if it is no longer needed. (offset is entirely past it.) + final byte[] chunk = chunks.peek(); + final long amountToAdvance = Math.min(offset - cursor, chunk.length - positionWithinFirstChunk); + cursor += amountToAdvance; + positionWithinFirstChunk += Ints.checkedCast(amountToAdvance); + + if (positionWithinFirstChunk == chunk.length) { + chunks.poll(); + positionWithinFirstChunk = 0; + } + } + + if (chunks.isEmpty() || offset != cursor) { + throw DruidException.defensive( + "Expected cursor[%,d] to be caught up to offset[%,d] by this point, and to have nonzero chunks", + cursor, + offset + ); + } + + return Futures.immediateFuture(new ByteChunksInputStream(ImmutableList.copyOf(chunks), positionWithinFirstChunk)); + } + + @Override + public synchronized ReadableFrameChannel readLocally() + { + if (state == State.INIT) { + state = State.LOCAL; + return channel; + } else if (state == State.REMOTE) { + throw new ISE("Cannot read both remotely and locally"); + } else if (state == State.LOCAL) { + throw new ISE("Cannot read channel multiple times"); + } else { + assert state == State.CLOSED; + throw new ISE("Closed"); + } + } + + @Override + public synchronized void close() + { + // Call channel.close() unless readLocally() has been called. In that case, we expect the caller to close it. + if (state != State.LOCAL) { + channel.close(); + } + } + + /** + * Input stream that can have bytes appended to it, and that can have bytes acknowledged. + */ + private class ChunkAcceptor implements WritableByteChannel + { + private boolean open = true; + + @Override + public int write(final ByteBuffer src) throws IOException + { + if (!open) { + throw new IOException("Closed"); + } + + final int len = src.remaining(); + if (len > 0) { + final byte[] bytes = new byte[len]; + src.get(bytes); + chunks.add(bytes); Review Comment: my thoughts: a) I think the copy can be eliminated if we alter `FrameFileWriter` somehow. It accepts a `WritableByteChannel` that it writes the frame file to, and the `WritableByteChannel` method `int write(ByteBuffer src)` requires copying the bytes from `src`. (The ByteBuffer object cannot be retained, since the caller might reuse it.) So, we'd need to change `FrameFileWriter` to have some option other than `WritableByteChannel`. b) I haven't done extensive profiling, so I'm not sure. I was planning to do more extensive profiling and look into further perf enhancements after this code lands in master. c) If there's any overhead, it wasn't present in the original code, because this entire code path is new. This code path is only used for in-memory shuffles. The original code always read from on-disk frame files, & did not generate them on-the-fly. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
