ibessonov commented on code in PR #1720: URL: https://github.com/apache/ignite-3/pull/1720#discussion_r1122671569
########## modules/table/src/main/java/org/apache/ignite/internal/table/distributed/gc/MvGc.java: ########## @@ -0,0 +1,249 @@ +/* + * 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.ignite.internal.table.distributed.gc; + +import static java.util.concurrent.CompletableFuture.completedFuture; +import static org.apache.ignite.internal.util.IgniteUtils.shutdownAndAwaitTermination; + +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentMap; +import java.util.concurrent.ExecutorService; +import java.util.concurrent.LinkedBlockingQueue; +import java.util.concurrent.ThreadPoolExecutor; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.atomic.AtomicBoolean; +import java.util.concurrent.atomic.AtomicReference; +import java.util.function.Supplier; +import org.apache.ignite.internal.close.ManuallyCloseable; +import org.apache.ignite.internal.hlc.HybridTimestamp; +import org.apache.ignite.internal.logger.IgniteLogger; +import org.apache.ignite.internal.logger.Loggers; +import org.apache.ignite.internal.storage.MvPartitionStorage; +import org.apache.ignite.internal.table.distributed.StorageUpdateHandler; +import org.apache.ignite.internal.table.distributed.replicator.TablePartitionId; +import org.apache.ignite.internal.thread.NamedThreadFactory; +import org.apache.ignite.internal.util.IgniteSpinBusyLock; +import org.apache.ignite.lang.ErrorGroups.Gc; +import org.apache.ignite.lang.IgniteInternalException; + +/** + * Garbage collector for multi-versioned storages and their indexes in the background. + * + * @see MvPartitionStorage#pollForVacuum(HybridTimestamp) + */ +public class MvGc implements ManuallyCloseable { + private static final IgniteLogger LOG = Loggers.forClass(MvGc.class); + + /** GC batch size for the storage. */ + static final int GC_BUTCH_SIZE = 5; + + /** Garbage collection thread pool. */ + private final ExecutorService executor; + + /** Prevents double closing. */ + private final AtomicBoolean closeGuard = new AtomicBoolean(); + + /** Busy lock to close synchronously. */ + private final IgniteSpinBusyLock busyLock = new IgniteSpinBusyLock(); + + /** Low watermark. */ + private final AtomicReference<HybridTimestamp> lowWatermarkReference = new AtomicReference<>(); + + /** Storage handler by table partition ID for which garbage will be collected. */ + private final ConcurrentMap<TablePartitionId, GcStorageHandler> storageHandlerByPartitionId = new ConcurrentHashMap<>(); + + /** + * Constructor. + * + * @param nodeName Node name. + * @param threadCount Number of garbage collector threads. + */ + public MvGc(String nodeName, int threadCount) { + assert threadCount > 0 : threadCount; + + executor = new ThreadPoolExecutor( + threadCount, + threadCount, + 30, + TimeUnit.SECONDS, + new LinkedBlockingQueue<>(), + new NamedThreadFactory(nodeName, LOG) + ); + } + + /** + * Adds storage for background garbage collection when updating a low watermark. + * + * @param tablePartitionId Table partition ID. + * @param storageUpdateHandler Storage update handler. + * @throws IgniteInternalException with {@link Gc#CLOSED_ERR} If the garbage collector is closed. + */ + public void addStorage(TablePartitionId tablePartitionId, StorageUpdateHandler storageUpdateHandler) { + inBusyLock(() -> { + GcStorageHandler previous = storageHandlerByPartitionId.putIfAbsent( + tablePartitionId, + new GcStorageHandler(storageUpdateHandler) + ); + + if (previous == null && lowWatermarkReference.get() != null) { + scheduleGcForStorage(tablePartitionId); + } + }); + } + + /** + * Removes storage for background garbage collection and completes the garbage collection for it. + * + * <p>Should be called before rebalancing/closing/destroying the storage. + * + * @param tablePartitionId Table partition ID. + * @return Storage garbage collection completion future. + * @throws IgniteInternalException with {@link Gc#CLOSED_ERR} If the garbage collector is closed. + */ + public CompletableFuture<Void> removeStorage(TablePartitionId tablePartitionId) { + return inBusyLock(() -> { + GcStorageHandler removed = storageHandlerByPartitionId.remove(tablePartitionId); + + if (removed == null) { + return completedFuture(null); + } + + CompletableFuture<Void> gcInProgressFuture = removed.gcInProgressFuture.get(); + + return gcInProgressFuture == null ? completedFuture(null) : gcInProgressFuture; + }); + } + + /** + * Updates the new watermark only if it is larger than the current low watermark. + * + * <p>If the update is successful, it will schedule a new garbage collection for all storages. + * + * @param newLwm New low watermark. + * @throws IgniteInternalException with {@link Gc#CLOSED_ERR} If the garbage collector is closed. + */ + public void updateLowWatermark(HybridTimestamp newLwm) { + inBusyLock(() -> { + HybridTimestamp updatedLwm = lowWatermarkReference.updateAndGet(currentLwm -> { + if (currentLwm == null) { + return newLwm; + } + + // Update only if the new one is greater than the current one. + return newLwm.compareTo(currentLwm) > 0 ? newLwm : currentLwm; + }); + + // If the new watermark is smaller than the current one or has been updated in parallel, then we do nothing. + if (updatedLwm != newLwm) { + return; + } + + executor.submit(() -> inBusyLock(this::initNewGcBusy)); + }); + } + + @Override + public void close() throws Exception { + if (!closeGuard.compareAndSet(false, true)) { + return; + } + + busyLock.block(); + + shutdownAndAwaitTermination(executor, 10, TimeUnit.SECONDS); + } + + private void initNewGcBusy() { + storageHandlerByPartitionId.keySet().forEach(this::scheduleGcForStorage); + } + + private void scheduleGcForStorage(TablePartitionId tablePartitionId) { + executor.submit(() -> inBusyLock(() -> { + GcStorageHandler storageHandler = storageHandlerByPartitionId.compute(tablePartitionId, (id, gcStorageHandler) -> { + if (gcStorageHandler == null) { + // Storage has been removed from garbage collection. + return gcStorageHandler; + } + + boolean casResult = gcStorageHandler.gcInProgressFuture.compareAndSet(null, new CompletableFuture<>()); Review Comment: Can you please clarify, what exactly you don't understand? 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