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[KeyValueSnapshotReader Phase I] Part 2: ReadValidationCommitTimestam…
…pLoader (#7017) * CTL * self cr part 1 * self CR part 2 * update javadoc * push comment out to javadoc * Split out read validation * ideas * original flavouring * no need to spam eq * edge case * polish * Not Jetbrains * CR * new world * sleepy stuff * self cr * circle not running? * fix
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.../main/java/com/palantir/atlasdb/transaction/impl/ReadValidationCommitTimestampLoader.java
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| /* | ||
| * (c) Copyright 2024 Palantir Technologies Inc. All rights reserved. | ||
| * | ||
| * Licensed 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 com.palantir.atlasdb.transaction.impl; | ||
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|
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| import com.google.common.util.concurrent.Futures; | ||
| import com.google.common.util.concurrent.ListenableFuture; | ||
| import com.google.common.util.concurrent.MoreExecutors; | ||
| import com.palantir.atlasdb.futures.AtlasFutures; | ||
| import com.palantir.atlasdb.keyvalue.api.TableReference; | ||
| import com.palantir.atlasdb.transaction.api.CommitTimestampLoader; | ||
| import com.palantir.atlasdb.transaction.api.TransactionSerializableConflictException; | ||
| import com.palantir.atlasdb.transaction.impl.SerializableTransaction.PartitionedTimestamps; | ||
| import com.palantir.atlasdb.transaction.impl.metrics.TransactionOutcomeMetrics; | ||
| import javax.annotation.Nullable; | ||
| import org.eclipse.collections.api.LongIterable; | ||
| import org.eclipse.collections.api.factory.primitive.LongLongMaps; | ||
| import org.eclipse.collections.api.factory.primitive.LongSets; | ||
| import org.eclipse.collections.api.map.primitive.LongLongMap; | ||
| import org.eclipse.collections.api.map.primitive.MutableLongLongMap; | ||
| import org.eclipse.collections.api.set.primitive.LongSet; | ||
| import org.eclipse.collections.api.set.primitive.MutableLongSet; | ||
|
|
||
| /** | ||
| * Loads commit timestamps for read validation, considering a simulated state of the world where the serializable | ||
| * transaction that we're performing validation for has already committed. | ||
| */ | ||
| public final class ReadValidationCommitTimestampLoader implements CommitTimestampLoader { | ||
| private final CommitTimestampLoader delegate; | ||
| private final long startTs; | ||
| private final long commitTs; | ||
| private final TransactionOutcomeMetrics transactionOutcomeMetrics; | ||
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| public ReadValidationCommitTimestampLoader( | ||
| CommitTimestampLoader delegate, | ||
| long startTs, | ||
| long commitTs, | ||
| TransactionOutcomeMetrics transactionOutcomeMetrics) { | ||
| this.delegate = delegate; | ||
| this.startTs = startTs; | ||
| this.commitTs = commitTs; | ||
| this.transactionOutcomeMetrics = transactionOutcomeMetrics; | ||
| } | ||
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| @Override | ||
| public ListenableFuture<LongLongMap> getCommitTimestamps( | ||
| @Nullable TableReference tableRef, LongIterable startTimestamps) { | ||
| return getCommitTimestampsInternal(tableRef, startTimestamps, true); | ||
| } | ||
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| @Override | ||
| public ListenableFuture<LongLongMap> getCommitTimestampsNonBlockingForValidation( | ||
| @Nullable TableReference tableRef, LongIterable startTimestamps) { | ||
| return getCommitTimestampsInternal(tableRef, startTimestamps, false); | ||
| } | ||
|
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| private ListenableFuture<LongLongMap> getCommitTimestampsInternal( | ||
| @Nullable TableReference tableRef, LongIterable startTimestamps, boolean shouldWaitForCommitterToComplete) { | ||
| PartitionedTimestamps partitionedTimestamps = splitTransactionBeforeAndAfter(startTs, startTimestamps); | ||
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| ListenableFuture<LongLongMap> postStartCommitTimestamps = | ||
| getCommitTimestampsForTransactionsStartedAfterMe(tableRef, partitionedTimestamps.afterStart()); | ||
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| // We are ok to block here because if there is a cycle of transactions that could result in a deadlock, | ||
| // then at least one of them will be in the ab | ||
| ListenableFuture<LongLongMap> preStartCommitTimestamps; | ||
| if (partitionedTimestamps.beforeStart().isEmpty()) { | ||
| // TODO (jkong): If called frequently, can consider memoisation. | ||
| preStartCommitTimestamps = Futures.immediateFuture(LongLongMaps.immutable.empty()); | ||
| } else { | ||
| if (shouldWaitForCommitterToComplete) { | ||
| preStartCommitTimestamps = delegate.getCommitTimestamps(tableRef, partitionedTimestamps.beforeStart()); | ||
| } else { | ||
| preStartCommitTimestamps = delegate.getCommitTimestampsNonBlockingForValidation( | ||
| tableRef, partitionedTimestamps.beforeStart()); | ||
| } | ||
| } | ||
|
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| return Futures.whenAllComplete(postStartCommitTimestamps, preStartCommitTimestamps) | ||
| .call( | ||
| () -> { | ||
| MutableLongLongMap map = | ||
| LongLongMaps.mutable.withAll(AtlasFutures.getDone(preStartCommitTimestamps)); | ||
| map.putAll(AtlasFutures.getDone(postStartCommitTimestamps)); | ||
| map.putAll(partitionedTimestamps.myCommittedTransaction()); | ||
| return map.toImmutable(); | ||
| }, | ||
| MoreExecutors.directExecutor()); | ||
| } | ||
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| private ListenableFuture<LongLongMap> getCommitTimestampsForTransactionsStartedAfterMe( | ||
| @Nullable TableReference tableRef, LongSet startTimestamps) { | ||
| if (startTimestamps.isEmpty()) { | ||
| return Futures.immediateFuture(LongLongMaps.immutable.empty()); | ||
| } | ||
|
|
||
| return Futures.transform( | ||
| // We do not block when waiting for results that were written after our start timestamp. | ||
| // If we block here it may lead to deadlock if two transactions (or a cycle of any length) have | ||
| // all written their data and all doing checks before committing. | ||
| delegate.getCommitTimestampsNonBlockingForValidation(tableRef, startTimestamps), | ||
| startToCommitTimestamps -> { | ||
| if (startToCommitTimestamps.keySet().containsAll(startTimestamps)) { | ||
| return startToCommitTimestamps; | ||
| } | ||
| // If we do not get back all these results we may be in the deadlock case so we | ||
| // should just fail out early. It may be the case that abort more transactions | ||
| // than needed to break the deadlock cycle, but this should be pretty rare. | ||
| transactionOutcomeMetrics.markReadWriteConflict(tableRef); | ||
| throw new TransactionSerializableConflictException( | ||
| "An uncommitted conflicting read was written after our start timestamp for table " | ||
| + tableRef + ". This case can cause deadlock and is very likely to be a " | ||
| + "read write conflict.", | ||
| tableRef); | ||
| }, | ||
| MoreExecutors.directExecutor()); | ||
| } | ||
|
|
||
| /** | ||
| * Partitions {@code startTimestamps} in two sets, based on their relation to the start timestamp provided. | ||
| * | ||
| * @param myStart start timestamp of this transaction | ||
| * @param startTimestamps of transactions we are interested in | ||
| * @return a {@link PartitionedTimestamps} object containing split timestamps | ||
| */ | ||
| private PartitionedTimestamps splitTransactionBeforeAndAfter(long myStart, LongIterable startTimestamps) { | ||
| ImmutablePartitionedTimestamps.Builder builder = | ||
| ImmutablePartitionedTimestamps.builder().myCommitTimestamp(commitTs); | ||
| MutableLongSet beforeStart = LongSets.mutable.empty(); | ||
| MutableLongSet afterStart = LongSets.mutable.empty(); | ||
| startTimestamps.forEach(startTimestamp -> { | ||
| if (startTimestamp == myStart) { | ||
| builder.splittingStartTimestamp(myStart); | ||
| } else if (startTimestamp < myStart) { | ||
| beforeStart.add(startTimestamp); | ||
| } else { | ||
| afterStart.add(startTimestamp); | ||
| } | ||
| }); | ||
| builder.beforeStart(beforeStart.asUnmodifiable()); | ||
| builder.afterStart(afterStart.asUnmodifiable()); | ||
| return builder.build(); | ||
| } | ||
| } |
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