maedhroz commented on code in PR #1723: URL: https://github.com/apache/cassandra/pull/1723#discussion_r983720333
########## src/java/org/apache/cassandra/db/tries/MemtableTrie.java: ########## @@ -0,0 +1,1039 @@ +/* + * 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.cassandra.db.tries; + +import java.nio.ByteBuffer; +import java.util.Arrays; +import java.util.Iterator; +import java.util.NoSuchElementException; +import java.util.concurrent.atomic.AtomicReferenceArray; + +import com.google.common.annotations.VisibleForTesting; + +import org.agrona.concurrent.UnsafeBuffer; +import org.apache.cassandra.io.compress.BufferType; +import org.apache.cassandra.io.util.FileUtils; +import org.apache.cassandra.utils.bytecomparable.ByteSource; +import org.apache.cassandra.utils.bytecomparable.ByteComparable; +import org.apache.cassandra.utils.ObjectSizes; +import org.github.jamm.MemoryLayoutSpecification; + +/** + * Memtable trie, i.e. an in-memory trie built for fast modification and reads executing concurrently with writes from + * a single mutator thread. + * + * Writes to this should be atomic (i.e. reads should see either the content before the write, or the content after the + * write; if any read sees the write, then any subsequent (i.e. started after it completed) read should also see it). + * This implementation does not currently guarantee this, but we still get the desired result as `apply` is only used + * with singleton tries. + */ +public class MemtableTrie<T> extends MemtableReadTrie<T> +{ + // See the trie format description in MemtableReadTrie. + + /** + * Trie size limit. This is not enforced, but users must check from time to time that it is not exceeded (using + * reachedAllocatedSizeThreshold()) and start switching to a new trie if it is. + * This must be done to avoid tries growing beyond their hard 2GB size limit (due to the 32-bit pointers). + */ + private static final int ALLOCATED_SIZE_THRESHOLD; + static + { + String propertyName = "dse.trie_size_limit_mb"; + // Default threshold + 10% == 1 GB. Adjusted slightly up to avoid a tiny final allocation for the 2G max. + int limitInMB = Integer.parseInt(System.getProperty(propertyName, + Integer.toString(1024 * 10 / 11 + 1))); + if (limitInMB < 1 || limitInMB > 2047) + throw new AssertionError(propertyName + " must be within 1 and 2047"); + ALLOCATED_SIZE_THRESHOLD = 1024 * 1024 * limitInMB; + } + + private int allocatedPos = 0; + private int contentCount = 0; + + private final BufferType bufferType; // on or off heap + + // constants for space calculations + private static final long EMPTY_SIZE_ON_HEAP; + private static final long EMPTY_SIZE_OFF_HEAP; + private static final long REFERENCE_ARRAY_ON_HEAP_SIZE = ObjectSizes.measureDeep(new AtomicReferenceArray<>(0)); + + static + { + MemtableTrie<Object> empty = new MemtableTrie<>(BufferType.ON_HEAP); + EMPTY_SIZE_ON_HEAP = ObjectSizes.measureDeep(empty); + empty = new MemtableTrie<>(BufferType.OFF_HEAP); + EMPTY_SIZE_OFF_HEAP = ObjectSizes.measureDeep(empty); + } + + public MemtableTrie(BufferType bufferType) + { + super(new UnsafeBuffer[31 - BUF_START_SHIFT], // last one is 1G for a total of ~2G bytes + new AtomicReferenceArray[29 - CONTENTS_START_SHIFT], // takes at least 4 bytes to write pointer to one content -> 4 times smaller than buffers + NONE); + this.bufferType = bufferType; + assert INITIAL_BUFFER_CAPACITY % BLOCK_SIZE == 0; + } + + // Buffer, content list and block management + + public static class SpaceExhaustedException extends Exception + { + public SpaceExhaustedException() + { + super("The hard 2GB limit on trie size has been exceeded"); + } + } + + final void putInt(int pos, int value) + { + getChunk(pos).putInt(inChunkPointer(pos), value); + } + + final void putIntOrdered(int pos, int value) + { + getChunk(pos).putIntOrdered(inChunkPointer(pos), value); + } + + final void putIntVolatile(int pos, int value) + { + getChunk(pos).putIntVolatile(inChunkPointer(pos), value); + } + + final void putShort(int pos, short value) + { + getChunk(pos).putShort(inChunkPointer(pos), value); + } + + final void putShortVolatile(int pos, short value) + { + getChunk(pos).putShort(inChunkPointer(pos), value); + } + + final void putByte(int pos, byte value) + { + getChunk(pos).putByte(inChunkPointer(pos), value); + } + + + private int allocateBlock() throws SpaceExhaustedException + { + // Note: If this method is modified, please run MemtableTrieTest.testOver1GSize to verify it acts correctly + // close to the 2G limit. + int v = allocatedPos; + if (inChunkPointer(v) == 0) + { + int leadBit = getChunkIdx(v, BUF_START_SHIFT, BUF_START_SIZE); + if (leadBit == 31) + throw new SpaceExhaustedException(); + + assert buffers[leadBit] == null; + ByteBuffer newBuffer = bufferType.allocate(BUF_START_SIZE << leadBit); + buffers[leadBit] = new UnsafeBuffer(newBuffer); + // The above does not contain any happens-before enforcing writes, thus at this point the new buffer may be + // invisible to any concurrent readers. Touching the volatile root pointer (which any new read must go + // through) enforces a happens-before that makes it visible to all new reads (note: when the write completes + // it must do some volatile write, but that will be in the new buffer and without the line below could + // remain unreachable by other cores). + root = root; + } + + allocatedPos += BLOCK_SIZE; + return v; + } + + private int addContent(T value) + { + int index = contentCount++; + int leadBit = getChunkIdx(index, CONTENTS_START_SHIFT, CONTENTS_START_SIZE); + int ofs = inChunkPointer(index, leadBit, CONTENTS_START_SIZE); + AtomicReferenceArray<T> array = contentArrays[leadBit]; + if (array == null) + { + assert ofs == 0; + contentArrays[leadBit] = array = new AtomicReferenceArray<>(CONTENTS_START_SIZE << leadBit); + } + array.lazySet(ofs, value); // no need for a volatile set here; at this point the item is not referenced + // by any node in the trie, and a volatile set will be made to reference it. + return index; + } + + private void setContent(int index, T value) + { + int leadBit = getChunkIdx(index, CONTENTS_START_SHIFT, CONTENTS_START_SIZE); + int ofs = inChunkPointer(index, leadBit, CONTENTS_START_SIZE); + AtomicReferenceArray<T> array = contentArrays[leadBit]; + array.set(ofs, value); + } + + public void discardBuffers() Review Comment: nit: Looks like an untested codepath, at least in the commit that added it, but perhaps it's tested via `TrieMemtable` somewhere else? -- 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]
