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/*
* Copyright (C) 2023-2024 Hedera Hashgraph, LLC
*
* 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.swirlds.merkledb.files;
import static com.swirlds.logging.legacy.LogMarker.EXCEPTION;
import static com.swirlds.logging.legacy.LogMarker.MERKLE_DB;
import static com.swirlds.merkledb.files.DataFileCommon.formatSizeBytes;
import static com.swirlds.merkledb.files.DataFileCommon.getSizeOfFiles;
import static com.swirlds.merkledb.files.DataFileCommon.getSizeOfFilesByPath;
import static com.swirlds.merkledb.files.DataFileCommon.logCompactStats;
import com.hedera.pbj.runtime.io.buffer.BufferedData;
import com.swirlds.base.units.UnitConstants;
import com.swirlds.merkledb.KeyRange;
import com.swirlds.merkledb.collections.CASableLongIndex;
import com.swirlds.merkledb.config.MerkleDbConfig;
import edu.umd.cs.findbugs.annotations.Nullable;
import java.io.IOException;
import java.nio.channels.ClosedByInterruptException;
import java.nio.file.Path;
import java.time.Instant;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiConsumer;
import java.util.stream.Collectors;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
/**
* This class is responsible performing compaction of data files in a {@link DataFileCollection}.
* The compaction is supposed to happen in the background and can be paused and resumed with {@link #pauseCompaction()}
* and {@link #resumeCompaction()} to prevent compaction from interfering with snapshots.
*
* @param data file type
*/
public class DataFileCompactor {
private static final Logger logger = LogManager.getLogger(DataFileCompactor.class);
/**
* This is the compaction level that non-compacted files have.
*/
public static final int INITIAL_COMPACTION_LEVEL = 0;
private final MerkleDbConfig dbConfig;
/**
* Name of the file store to compact.
*/
private final String storeName;
/**
* The data file collection to compact
*/
private final DataFileCollection dataFileCollection;
/**
* Index to update during compaction
*/
private final CASableLongIndex index;
/**
* A function that will be called to report the duration of the compaction
*/
@Nullable
private final BiConsumer reportDurationMetricFunction;
/**
* A function that will be called to report the amount of space saved by the compaction
*/
@Nullable
private final BiConsumer reportSavedSpaceMetricFunction;
private final BiConsumer reportFileSizeByLevelMetricFunction;
/**
* A function that updates statistics of total usage of disk space and off-heap space
*/
@Nullable
private final Runnable updateTotalStatsFunction;
/**
* A lock used for synchronization between snapshots and compactions. While a compaction is in
* progress, it runs on its own without any synchronization. However, a few critical sections
* are protected with this lock: to create a new compaction writer/reader when compaction is
* started, to copy data items to the current writer and update the corresponding index item,
* and to close the compaction writer. This mechanism allows snapshots to effectively put
* compaction on hold, which is critical as snapshots should be as fast as possible, while
* compactions are just background processes.
*/
private final Semaphore snapshotCompactionLock = new Semaphore(1);
/**
* Start time of the current compaction, or null if compaction isn't running
*/
private final AtomicReference currentCompactionStartTime = new AtomicReference<>();
/**
* Current data file writer during compaction, or null if compaction isn't running. The writer
* is created at compaction start. If compaction is interrupted by a snapshot, the writer is
* closed before the snapshot, and then a new writer / new file is created after the snapshot is
* taken.
*/
private final AtomicReference> currentWriter = new AtomicReference<>();
/**
* Currrent data file reader for the compaction writer above.
*/
private final AtomicReference> currentReader = new AtomicReference<>();
/**
* The list of new files created during compaction. Usually, all files to process are compacted
* to a single new file, but if compaction is interrupted by a snapshot, there may be more than
* one file created.
*/
private final List newCompactedFiles = new ArrayList<>();
/**
* Indicates whether compaction is in progress at the time when {@link #pauseCompaction()}
* is called. This flag is then checked in {@link DataFileCompactor#resumeCompaction()} )} to start a new
* compacted file or not.
*/
private final AtomicBoolean compactionWasInProgress = new AtomicBoolean(false);
/**
* This variable keeps track of the compaction level that was in progress at the time when it was suspended.
* Once the compaction is resumed, this level is used to start a new compacted file, and then it's reset to 0.
*/
private final AtomicInteger compactionLevelInProgress = new AtomicInteger(0);
/**
* @param dbConfig MerkleDb config
* @param storeName name of the store to compact
* @param dataFileCollection data file collection to compact
* @param index index to update during compaction
* @param reportDurationMetricFunction function to report how long compaction took, in ms
* @param reportSavedSpaceMetricFunction function to report how much space was compacted, in Mb
* @param reportFileSizeByLevelMetricFunction function to report how much spaсе is used by the store by compaction level, in Mb
* @param updateTotalStatsFunction A function that updates statistics of total usage of disk space and off-heap space
*/
public DataFileCompactor(
final MerkleDbConfig dbConfig,
final String storeName,
final DataFileCollection dataFileCollection,
CASableLongIndex index,
@Nullable final BiConsumer reportDurationMetricFunction,
@Nullable final BiConsumer reportSavedSpaceMetricFunction,
@Nullable final BiConsumer reportFileSizeByLevelMetricFunction,
@Nullable Runnable updateTotalStatsFunction) {
this.dbConfig = dbConfig;
this.storeName = storeName;
this.dataFileCollection = dataFileCollection;
this.index = index;
this.reportDurationMetricFunction = reportDurationMetricFunction;
this.reportSavedSpaceMetricFunction = reportSavedSpaceMetricFunction;
this.reportFileSizeByLevelMetricFunction = reportFileSizeByLevelMetricFunction;
this.updateTotalStatsFunction = updateTotalStatsFunction;
}
/**
* Compacts all files in compactionPlan.
*
* @param index takes a map of moves from old location to new location. Once it is finished and
* returns it is assumed all readers will no longer be looking in old location, so old files
* can be safely deleted.
* @param filesToCompact list of files to compact
* @param targetCompactionLevel target compaction level
* @return list of files created during the compaction
* @throws IOException If there was a problem with the compaction
* @throws InterruptedException If the compaction thread was interrupted
*/
synchronized List compactFiles(
final CASableLongIndex index,
final List> filesToCompact,
final int targetCompactionLevel)
throws IOException, InterruptedException {
if (filesToCompact.size() < getMinNumberOfFilesToCompact()) {
// nothing to do we have merged since the last data update
logger.debug(MERKLE_DB.getMarker(), "No files were available for merging [{}]", storeName);
return Collections.emptyList();
}
// create a merge time stamp, this timestamp is the newest time of the set of files we are
// merging
final Instant startTime = filesToCompact.stream()
.map(file -> file.getMetadata().getCreationDate())
.max(Instant::compareTo)
.orElseGet(Instant::now);
snapshotCompactionLock.acquire();
try {
currentCompactionStartTime.set(startTime);
newCompactedFiles.clear();
startNewCompactionFile(targetCompactionLevel);
} finally {
snapshotCompactionLock.release();
}
// We need a map to find readers by file index below. It doesn't have to be synchronized
// as it will be accessed in this thread only, so it can be a simple HashMap or alike.
// However, standard Java maps can only work with Integer, not int (yet), so auto-boxing
// will put significant load on GC. Let's do something different
int minFileIndex = Integer.MAX_VALUE;
int maxFileIndex = 0;
for (final DataFileReader r : filesToCompact) {
minFileIndex = Math.min(minFileIndex, r.getIndex());
maxFileIndex = Math.max(maxFileIndex, r.getIndex());
}
final int firstIndexInc = minFileIndex;
final int lastIndexExc = maxFileIndex + 1;
final DataFileReader[] readers = new DataFileReader[lastIndexExc - firstIndexInc];
for (DataFileReader r : filesToCompact) {
readers[r.getIndex() - firstIndexInc] = r;
}
boolean allDataItemsProcessed = false;
try {
final KeyRange keyRange = dataFileCollection.getValidKeyRange();
index.forEach((path, dataLocation) -> {
if (!keyRange.withinRange(path)) {
return;
}
final int fileIndex = DataFileCommon.fileIndexFromDataLocation(dataLocation);
if ((fileIndex < firstIndexInc) || (fileIndex >= lastIndexExc)) {
return;
}
final DataFileReader reader = readers[fileIndex - firstIndexInc];
if (reader == null) {
return;
}
final long fileOffset = DataFileCommon.byteOffsetFromDataLocation(dataLocation);
// Take the lock. If a snapshot is started in a different thread, this call
// will block until the snapshot is done. The current file will be flushed,
// and current data file writer and reader will point to a new file
snapshotCompactionLock.acquire();
try {
final DataFileWriter newFileWriter = currentWriter.get();
final BufferedData itemBytes = reader.readDataItemBytes(fileOffset);
assert itemBytes != null;
long newLocation = newFileWriter.writeCopiedDataItem(itemBytes);
// update the index
index.putIfEqual(path, dataLocation, newLocation);
} catch (final ClosedByInterruptException e) {
logger.info(
MERKLE_DB.getMarker(),
"Failed to copy data item {} / {} due to thread interruption",
fileIndex,
fileOffset,
e);
throw e;
} catch (final IOException z) {
logger.error(EXCEPTION.getMarker(), "Failed to copy data item {} / {}", fileIndex, fileOffset, z);
throw z;
} finally {
snapshotCompactionLock.release();
}
});
allDataItemsProcessed = true;
} finally {
// Even if the thread is interrupted, make sure the new compacted file is properly closed
// and is included to future compactions
snapshotCompactionLock.acquire();
try {
// Finish writing the last file. In rare cases, it may be an empty file
finishCurrentCompactionFile();
// Clear compaction start time
currentCompactionStartTime.set(null);
if (allDataItemsProcessed) {
// Close the readers and delete compacted files
dataFileCollection.deleteFiles(filesToCompact);
}
} finally {
snapshotCompactionLock.release();
}
}
return newCompactedFiles;
}
// visible for testing
int getMinNumberOfFilesToCompact() {
return dbConfig.minNumberOfFilesInCompaction();
}
/**
* Opens a new file for writing during compaction. This method is called, when compaction is
* started. If compaction is interrupted and resumed by data source snapshot using {@link
* #pauseCompaction()} and {@link #resumeCompaction()}, a new file is created for writing using
* this method before compaction is resumed.
*
* This method must be called under snapshot/compaction lock.
*
* @throws IOException If an I/O error occurs
*/
private void startNewCompactionFile(int compactionLevel) throws IOException {
final Instant startTime = currentCompactionStartTime.get();
assert startTime != null;
final DataFileWriter newFileWriter = dataFileCollection.newDataFile(startTime, compactionLevel);
currentWriter.set(newFileWriter);
final Path newFileCreated = newFileWriter.getPath();
newCompactedFiles.add(newFileCreated);
final DataFileMetadata newFileMetadata = newFileWriter.getMetadata();
final DataFileReader newFileReader =
dataFileCollection.addNewDataFileReader(newFileCreated, newFileMetadata);
currentReader.set(newFileReader);
}
/**
* Closes the current compaction file. This method is called in the end of compaction process,
* and also before a snapshot is taken to make sure the current file is fully written and safe
* to include to snapshots.
*
* This method must be called under snapshot/compaction lock.
*
* @throws IOException If an I/O error occurs
*/
private void finishCurrentCompactionFile() throws IOException {
currentWriter.get().finishWriting();
currentWriter.set(null);
// Now include the file in future compactions
currentReader.get().setFileCompleted();
currentReader.set(null);
}
/**
* Puts file compaction on hold, if it's currently in progress. If not in progress, it will
* prevent compaction from starting until {@link #resumeCompaction()} is called. The most
* important thing this method does is it makes data files consistent and read only, so they can
* be included to snapshots as easily as to create hard links. In particular, if compaction is
* in progress, and a new data file is being written to, this file is flushed to disk, no files
* are created and no index entries are updated until compaction is resumed.
*
* This method should not be called on the compaction thread.
*
* This method must be always balanced with and called before {@link DataFileCompactor#resumeCompaction()}. If
* there are more / less calls to resume compactions than to pause, or if they are called in a
* wrong order, it will result in deadlocks.
*
* @throws IOException If an I/O error occurs
* @see #resumeCompaction()
*/
public void pauseCompaction() throws IOException {
snapshotCompactionLock.acquireUninterruptibly();
// Check if compaction is currently in progress. If so, flush and close the current file, so
// it's included to the snapshot
final DataFileWriter compactionWriter = currentWriter.get();
if (compactionWriter != null) {
compactionWasInProgress.set(true);
compactionLevelInProgress.set(compactionWriter.getMetadata().getCompactionLevel());
finishCurrentCompactionFile();
// Don't start a new compaction file here, as it would be included to snapshots, but
// it shouldn't, as it isn't fully written yet. Instead, a new file will be started
// right after snapshot is taken, in resumeCompaction()
}
// Don't release the lock here, it will be done later in resumeCompaction(). If there is no
// compaction currently running, the lock will prevent starting a new one until snapshot is
// done
}
/**
* Resumes compaction previously put on hold with {@link #pauseCompaction()}. If there was no
* compaction running at that moment, but new compaction was started (and blocked) since {@link
* #pauseCompaction()}, this new compaction is resumed.
*
* This method must be always balanced with and called after {@link #pauseCompaction()}. If
* there are more / less calls to resume compactions than to pause, or if they are called in a
* wrong order, it will result in deadlocks.
*
* @throws IOException If an I/O error occurs
*/
public void resumeCompaction() throws IOException {
try {
if (compactionWasInProgress.getAndSet(false)) {
assert currentWriter.get() == null;
assert currentReader.get() == null;
startNewCompactionFile(compactionLevelInProgress.getAndSet(0));
}
} finally {
snapshotCompactionLock.release();
}
}
/**
* Compact data files in the collection according to the compaction algorithm.
*
* @throws IOException if there was a problem merging
* @throws InterruptedException if the merge thread was interrupted
* @return true if compaction was performed, false otherwise
*/
public boolean compact() throws IOException, InterruptedException {
final List> completedFiles = dataFileCollection.getAllCompletedFiles();
reportFileSizeByLevel(completedFiles);
final List> filesToCompact =
compactionPlan(completedFiles, getMinNumberOfFilesToCompact(), dbConfig.maxCompactionLevel());
if (filesToCompact.isEmpty()) {
logger.debug(MERKLE_DB.getMarker(), "[{}] No need to compact, as the compaction plan is empty", storeName);
return false;
}
final int filesCount = filesToCompact.size();
logger.info(MERKLE_DB.getMarker(), "[{}] Starting compaction", storeName);
final int targetCompactionLevel = getTargetCompactionLevel(filesToCompact, filesCount);
final long start = System.currentTimeMillis();
final long filesToCompactSize = getSizeOfFiles(filesToCompact);
logger.debug(
MERKLE_DB.getMarker(),
"[{}] Starting merging {} files / {}",
storeName,
filesCount,
formatSizeBytes(filesToCompactSize));
final List newFilesCreated = compactFiles(index, filesToCompact, targetCompactionLevel);
final long end = System.currentTimeMillis();
final long tookMillis = end - start;
if (reportDurationMetricFunction != null) {
reportDurationMetricFunction.accept(targetCompactionLevel, tookMillis);
}
final long compactedFilesSize = getSizeOfFilesByPath(newFilesCreated);
if (reportSavedSpaceMetricFunction != null) {
reportSavedSpaceMetricFunction.accept(
targetCompactionLevel,
(filesToCompactSize - compactedFilesSize) * UnitConstants.BYTES_TO_MEBIBYTES);
}
reportFileSizeByLevel(dataFileCollection.getAllCompletedFiles());
logCompactStats(
storeName,
tookMillis,
filesToCompact,
filesToCompactSize,
newFilesCreated,
targetCompactionLevel,
dataFileCollection);
logger.info(
MERKLE_DB.getMarker(),
"[{}] Finished compaction {} files / {} in {} ms",
storeName,
filesCount,
formatSizeBytes(filesToCompactSize),
tookMillis);
if (updateTotalStatsFunction != null) {
updateTotalStatsFunction.run();
}
return true;
}
private void reportFileSizeByLevel(List> allCompletedFiles) {
if (reportFileSizeByLevelMetricFunction != null) {
final Map>> readersByLevel = getReadersByLevel(allCompletedFiles);
for (int i = 0; i < readersByLevel.size(); i++) {
final List> readers = readersByLevel.get(i);
if (readers != null) {
reportFileSizeByLevelMetricFunction.accept(
i, getSizeOfFiles(readers) * UnitConstants.BYTES_TO_MEBIBYTES);
}
}
}
}
/**
* The target compaction level should not exceed the maxCompactionLevel configuration parameter.
* We need a limit on compaction levels for two reasons:
* - To ensure a reasonably predictable frequency for full compactions, even for data that changes infrequently.
* - We maintain metrics for each level, and there should be a cap on the number of these metrics.
*/
private int getTargetCompactionLevel(List> filesToCompact, int filesCount) {
int highestExistingCompactionLevel =
filesToCompact.get(filesCount - 1).getMetadata().getCompactionLevel();
return Math.min(highestExistingCompactionLevel + 1, dbConfig.maxCompactionLevel());
}
/**
* This method creates a compaction plan (a set of files to be compacted). The plan is organized by compaction levels
* in ascending order. If there are not enough files to compact, then no files are compacted and the plan will be empty.
* If the current level doesn't reach minNumberOfFilesToCompact threshold,
* then this level and the levels above it are not included in the plan.
* @return filter creating a compaction plan
*/
static List> compactionPlan(
List> dataFileReaders, int minNumberOfFilesToCompact, int maxCompactionLevel) {
if (dataFileReaders.isEmpty()) {
return dataFileReaders;
}
final Map>> readersByLevel = getReadersByLevel(dataFileReaders);
final List> nonCompactedReaders = readersByLevel.get(INITIAL_COMPACTION_LEVEL);
if (nonCompactedReaders == null || nonCompactedReaders.size() < minNumberOfFilesToCompact) {
return Collections.emptyList();
}
// we always compact files from level 0 if we have enough files
final List> readersToCompact = new ArrayList<>(nonCompactedReaders);
for (int i = 1; i <= maxCompactionLevel; i++) {
final List> readers = readersByLevel.get(i);
// Presumably, one file comes from the compaction of the previous level.
// If, counting this file in, it still doesn't have enough, then it stops collecting.
if (readers == null || readers.size() < minNumberOfFilesToCompact - 1) {
break;
}
readersToCompact.addAll(readers);
}
return readersToCompact;
}
private static Map>> getReadersByLevel(
final List> dataFileReaders) {
return dataFileReaders.stream()
.collect(Collectors.groupingBy(r -> r.getMetadata().getCompactionLevel()));
}
}