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/*-
* Copyright (C) 2002, 2018, Oracle and/or its affiliates. All rights reserved.
*
* This file was distributed by Oracle as part of a version of Oracle Berkeley
* DB Java Edition made available at:
*
* http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/downloads/index.html
*
* Please see the LICENSE file included in the top-level directory of the
* appropriate version of Oracle Berkeley DB Java Edition for a copy of the
* license and additional information.
*/
package com.sleepycat.je.incomp;
import static com.sleepycat.je.incomp.INCompStatDefinition.GROUP_DESC;
import static com.sleepycat.je.incomp.INCompStatDefinition.GROUP_NAME;
import static com.sleepycat.je.incomp.INCompStatDefinition.INCOMP_CURSORS_BINS;
import static com.sleepycat.je.incomp.INCompStatDefinition.INCOMP_DBCLOSED_BINS;
import static com.sleepycat.je.incomp.INCompStatDefinition.INCOMP_NON_EMPTY_BINS;
import static com.sleepycat.je.incomp.INCompStatDefinition.INCOMP_PROCESSED_BINS;
import static com.sleepycat.je.incomp.INCompStatDefinition.INCOMP_QUEUE_SIZE;
import static com.sleepycat.je.incomp.INCompStatDefinition.INCOMP_SPLIT_BINS;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.sleepycat.je.CacheMode;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.StatsConfig;
import com.sleepycat.je.cleaner.LocalUtilizationTracker;
import com.sleepycat.je.config.EnvironmentParams;
import com.sleepycat.je.dbi.DatabaseId;
import com.sleepycat.je.dbi.DatabaseImpl;
import com.sleepycat.je.dbi.DbTree;
import com.sleepycat.je.dbi.EnvironmentImpl;
import com.sleepycat.je.latch.LatchSupport;
import com.sleepycat.je.tree.BIN;
import com.sleepycat.je.tree.BINReference;
import com.sleepycat.je.tree.CursorsExistException;
import com.sleepycat.je.tree.IN;
import com.sleepycat.je.tree.NodeNotEmptyException;
import com.sleepycat.je.tree.Tree;
import com.sleepycat.je.utilint.DaemonThread;
import com.sleepycat.je.utilint.LoggerUtils;
import com.sleepycat.je.utilint.LongStat;
import com.sleepycat.je.utilint.StatGroup;
import com.sleepycat.je.utilint.TestHook;
import com.sleepycat.je.utilint.TestHookExecute;
/**
* JE compression consists of removing BIN slots for deleted and expired
* records, and pruning empty IN/BINs from the tree which is also called a
* reverse split.
*
* One of the reasons compression is treated specially is that slot compression
* cannot be performed inline as part of a delete operation. When we delete an
* LN, a cursor is always present on the LN. The API dictates that the cursor
* will remain positioned on the deleted record. In addition, if the deleting
* transaction aborts we must restore the slot and the possibility of a split
* during an abort is something we wish to avoid; for this reason, compression
* will not occur if the slot's LSN is locked. In principle, slot compression
* could be performed during transaction commit, but that would be expensive
* because a Btree lookup would be required, and this would negatively impact
* operation latency. For all these reasons, slot compression is performed
* after the delete operation is complete and committed, and not in the thread
* performing the operation or transaction commit.
*
* Compression is of two types:
*
* + "Queued compression" is carried out by the INCompressor daemon thread.
* Both slot compression and pruning are performed.
*
* + "Lazy compression" is carried out opportunistically at various times when
* compression is beneficial.
*
* The use of BIN-deltas has a big impact on slot compression because dirty
* slots cannot be compressed until we know that a full BIN will be logged
* next. If a dirty slot were compressed prior to logging a BIN-delta, the
* record of the compression would be lost and the slot would "reappear" when
* the BIN is reconstituted. Normally we do not compress dirty slots when a
* delta would next be logged. However, there are times when we do compress
* dirty slots, and in that case the "prohibit next logged delta" flag is set
* on the BIN.
*
* Queued compression prior to logging a BIN-delta is also wasteful because the
* dequeued entry cannot be processed. Therefore, lazy compression is relied
* on when a BIN-delta will next be logged. Because, BIN-deltas are logged
* more often than BINs, lazy compression is used for slot compression more
* often than queued compression.
*
* Lazy compression is used for compressing expired slots, in addition to
* deleted slots. This is done opportunistically as described above. Expired
* slots are normally not dirty, so they can often be compressed even when a
* BIN will be logged next as a BIN-delta. The same is true of deleted slots
* that are not dirty, although these occur infrequently.
*
* Since we don't lazy-compress BIN-deltas, how can we prevent their expired
* slots from using space for long time periods? Currently the expired space
* will be reclaimed only when the delta is mutated to a full BIN and then
* compressed, including when the full BIN is cleaned. This is the same as
* reclaiming space for deleted slots, so this is acceptable for now at least.
*
* You may wonder, since lazy compression is necessary, why use queued
* compression for slot compression at all? Queued compression is useful for
* the following reasons:
*
* + If a BIN-delta will not be logged next, queued compression will cause the
* compression to occur sooner than with lazy compression.
*
* + When a cursor is on a BIN or a deleted entry is locked during lazy
* compression, we cannot compress the slot. Queuing allows it to be
* compressed sooner than if we waited for the next lazy compression.
*
* + The code to process a queue entry must do slot compression anyway, even if
* we only want to prune the BIN. We have to account for the case where all
* slots are deleted but not yet compressed. So the code to process the
* queue entry could not be simplified even if we were to decide not to queue
* entries for slot compression.
*/
public class INCompressor extends DaemonThread {
private static final boolean DEBUG = false;
private final long lockTimeout;
/* stats */
private StatGroup stats;
private LongStat splitBins;
private LongStat dbClosedBins;
private LongStat cursorsBins;
private LongStat nonEmptyBins;
private LongStat processedBins;
private LongStat compQueueSize;
/* per-run stats */
private int splitBinsThisRun = 0;
private int dbClosedBinsThisRun = 0;
private int cursorsBinsThisRun = 0;
private int nonEmptyBinsThisRun = 0;
private int processedBinsThisRun = 0;
/*
* The following stats are not kept per run, because they're set by
* multiple threads doing lazy compression. They are debugging aids; it
* didn't seem like a good idea to add synchronization to the general path.
*/
private int lazyProcessed = 0;
private int wokenUp = 0;
/*
* Store logical references to BINs that have deleted entries and are
* candidates for compaction.
*/
private Map binRefQueue;
private final Object binRefQueueSync;
/* For unit tests */
private TestHook beforeFlushTrackerHook; // [#15528]
public INCompressor(EnvironmentImpl env, long waitTime, String name) {
super(waitTime, name, env);
lockTimeout = env.getConfigManager().getDuration
(EnvironmentParams.COMPRESSOR_LOCK_TIMEOUT);
binRefQueue = new HashMap<>();
binRefQueueSync = new Object();
/* Do the stats definitions. */
stats = new StatGroup(GROUP_NAME, GROUP_DESC);
splitBins = new LongStat(stats, INCOMP_SPLIT_BINS);
dbClosedBins = new LongStat(stats, INCOMP_DBCLOSED_BINS);
cursorsBins = new LongStat(stats, INCOMP_CURSORS_BINS);
nonEmptyBins = new LongStat(stats, INCOMP_NON_EMPTY_BINS);
processedBins = new LongStat(stats, INCOMP_PROCESSED_BINS);
compQueueSize = new LongStat(stats, INCOMP_QUEUE_SIZE);
}
/* For unit testing only. */
public void setBeforeFlushTrackerHook(TestHook hook) {
beforeFlushTrackerHook = hook;
}
public synchronized void verifyCursors()
throws DatabaseException {
/*
* Environment may have been closed. If so, then our job here is done.
*/
if (envImpl.isClosed()) {
return;
}
/*
* Use a snapshot to verify the cursors. This way we don't have to
* hold a latch while verify takes locks.
*/
final List queueSnapshot;
synchronized (binRefQueueSync) {
queueSnapshot = new ArrayList<>(binRefQueue.values());
}
/*
* Use local caching to reduce DbTree.getDb overhead. Do not call
* releaseDb after each getDb, since the entire dbCache will be
* released at the end.
*/
final DbTree dbTree = envImpl.getDbTree();
final Map dbCache = new HashMap<>();
try {
for (final BINReference binRef : queueSnapshot) {
final DatabaseImpl db = dbTree.getDb(
binRef.getDatabaseId(), lockTimeout, dbCache);
final BIN bin = searchForBIN(db, binRef);
if (bin != null) {
bin.verifyCursors();
bin.releaseLatch();
}
}
} finally {
dbTree.releaseDbs(dbCache);
}
}
public int getBinRefQueueSize() {
synchronized (binRefQueueSync) {
return binRefQueue.size();
}
}
/*
* There are multiple flavors of the addBin*ToQueue methods. All allow
* the caller to specify whether the daemon should be notified. Currently
* no callers proactively notify, and we rely on lazy compression and
* the daemon timebased wakeup to process the queue.
*/
/**
* Adds the BIN to the queue if the BIN is not already in the queue.
*/
public void addBinToQueue(BIN bin) {
synchronized (binRefQueueSync) {
addBinToQueueAlreadyLatched(bin);
}
}
/**
* Adds the BINReference to the queue if the BIN is not already in the
* queue.
*/
private void addBinRefToQueue(BINReference binRef) {
synchronized (binRefQueueSync) {
addBinRefToQueueAlreadyLatched(binRef);
}
}
/**
* Adds an entire collection of BINReferences to the queue at once. Use
* this to avoid latching for each add.
*/
public void addMultipleBinRefsToQueue(Collection binRefs) {
synchronized (binRefQueueSync) {
for (final BINReference binRef : binRefs) {
addBinRefToQueueAlreadyLatched(binRef);
}
}
}
/**
* Adds the BINReference with the latch held.
*/
private void addBinRefToQueueAlreadyLatched(BINReference binRef) {
final Long node = binRef.getNodeId();
if (binRefQueue.containsKey(node)) {
return;
}
binRefQueue.put(node, binRef);
}
/**
* Adds the BIN with the latch held.
*/
private void addBinToQueueAlreadyLatched(BIN bin) {
final Long node = bin.getNodeId();
if (binRefQueue.containsKey(node)) {
return;
}
binRefQueue.put(node, bin.createReference());
}
public boolean exists(long nodeId) {
synchronized (binRefQueueSync) {
return binRefQueue.containsKey(nodeId);
}
}
/**
* Return stats
*/
public StatGroup loadStats(StatsConfig config) {
compQueueSize.set((long) getBinRefQueueSize());
if (DEBUG) {
System.out.println("lazyProcessed = " + lazyProcessed);
System.out.println("wokenUp=" + wokenUp);
}
if (config.getClear()) {
lazyProcessed = 0;
wokenUp = 0;
}
return stats.cloneGroup(config.getClear());
}
/**
* Return the number of retries when a deadlock exception occurs.
*/
@Override
protected long nDeadlockRetries() {
return envImpl.getConfigManager().getInt
(EnvironmentParams.COMPRESSOR_RETRY);
}
@Override
public synchronized void onWakeup()
throws DatabaseException {
if (envImpl.isClosing()) {
return;
}
wokenUp++;
doCompress();
}
/**
* The real work to doing a compress. This may be called by the compressor
* thread or programatically.
*/
public synchronized void doCompress()
throws DatabaseException {
/*
* Make a snapshot of the current work queue so the compressor thread
* can safely iterate over the queue. Note that this impacts lazy
* compression, because it lazy compressors will not see BINReferences
* that have been moved to the snapshot.
*/
final Map queueSnapshot;
final int binQueueSize;
synchronized (binRefQueueSync) {
binQueueSize = binRefQueue.size();
if (binQueueSize <= 0) {
return;
}
queueSnapshot = binRefQueue;
binRefQueue = new HashMap<>();
}
/* There is work to be done. */
resetPerRunCounters();
LoggerUtils.fine(logger, envImpl,
"InCompress.doCompress called, queue size: " +
binQueueSize);
if (LatchSupport.TRACK_LATCHES) {
LatchSupport.expectBtreeLatchesHeld(0);
}
/*
* Compressed entries must be counted as obsoleted. A separate
* tracker is used to accumulate tracked obsolete info so it can be
* added in a single call under the log write latch. We log the
* info for deleted subtrees immediately because we don't process
* deleted IN entries during recovery; this reduces the chance of
* lost info.
*/
final LocalUtilizationTracker localTracker =
new LocalUtilizationTracker(envImpl);
/* Use local caching to reduce DbTree.getDb overhead. */
final Map dbCache = new HashMap<>();
final DbTree dbTree = envImpl.getDbTree();
final BINSearch binSearch = new BINSearch();
try {
for (final BINReference binRef : queueSnapshot.values()) {
if (envImpl.isClosed()) {
return;
}
if (!findDBAndBIN(binSearch, binRef, dbTree, dbCache)) {
/*
* Either the db is closed, or the BIN doesn't exist.
* Don't process this BINReference.
*/
continue;
}
/* Compress deleted slots and prune if possible. */
compressBin(binSearch.db, binSearch.bin, binRef, localTracker);
}
/* SR [#11144]*/
assert TestHookExecute.doHookIfSet(beforeFlushTrackerHook);
/*
* Count obsolete nodes and write out modified file summaries
* for recovery. All latches must have been released.
*/
envImpl.getUtilizationProfile().flushLocalTracker(localTracker);
} finally {
dbTree.releaseDbs(dbCache);
if (LatchSupport.TRACK_LATCHES) {
LatchSupport.expectBtreeLatchesHeld(0);
}
accumulatePerRunCounters();
}
}
/**
* Compresses a single BIN and then deletes the BIN if it is empty.
*
* @param bin is latched when this method is called, and unlatched when it
* returns.
*/
private void compressBin(
DatabaseImpl db,
BIN bin,
BINReference binRef,
LocalUtilizationTracker localTracker) {
/* Safe to get identifier keys; bin is latched. */
final byte[] idKey = bin.getIdentifierKey();
boolean empty = (bin.getNEntries() == 0);
try {
if (!empty) {
/*
* Deltas in cache cannot be compressed.
*
* We strive not to add a slot to the queue when we will log a
* delta. However, it is possible that an entry is added, or
* that an entry is not cleared by lazy compression prior to
* logging a full BIN. Clean-up for such queue entries is
* here.
*/
if (bin.isBINDelta()) {
return;
}
/* If there are cursors on the BIN, requeue and try later. */
if (bin.nCursors() > 0) {
addBinRefToQueue(binRef);
cursorsBinsThisRun++;
return;
}
/*
* If a delta should be logged, do not compress dirty slots,
* since this would prevent logging a delta.
*/
if (!bin.compress(
!bin.shouldLogDelta() /*compressDirtySlots*/,
localTracker)) {
/* If compression is incomplete, requeue and try later. */
addBinRefToQueue(binRef);
return;
}
/* After compression the BIN may be empty. */
empty = (bin.getNEntries() == 0);
}
} finally {
bin.releaseLatch();
}
/* After releasing the latch, prune the BIN if it is empty. */
if (empty) {
pruneBIN(db, binRef, idKey);
}
}
/**
* If the target BIN is empty, attempt to remove the empty branch of the
* tree.
*/
private void pruneBIN(DatabaseImpl dbImpl,
BINReference binRef,
byte[] idKey) {
try {
final Tree tree = dbImpl.getTree();
tree.delete(idKey);
processedBinsThisRun++;
} catch (NodeNotEmptyException NNEE) {
/*
* Something was added to the node since the point when the
* deletion occurred; we can't prune, and we can throw away this
* BINReference.
*/
nonEmptyBinsThisRun++;
} catch (CursorsExistException e) {
/* If there are cursors in the way of the delete, retry later. */
addBinRefToQueue(binRef);
cursorsBinsThisRun++;
}
}
/**
* Search the tree for the BIN that corresponds to this BINReference.
*
* @param binRef the BINReference that indicates the bin we want.
*
* @return the BIN that corresponds to this BINReference. The
* node is latched upon return. Returns null if the BIN can't be found.
*/
public BIN searchForBIN(DatabaseImpl db, BINReference binRef) {
return db.getTree().search(binRef.getKey(), CacheMode.UNCHANGED);
}
/**
* Reset per-run counters.
*/
private void resetPerRunCounters() {
splitBinsThisRun = 0;
dbClosedBinsThisRun = 0;
cursorsBinsThisRun = 0;
nonEmptyBinsThisRun = 0;
processedBinsThisRun = 0;
}
private void accumulatePerRunCounters() {
splitBins.add(splitBinsThisRun);
dbClosedBins.add(dbClosedBinsThisRun);
cursorsBins.add(cursorsBinsThisRun);
nonEmptyBins.add(nonEmptyBinsThisRun);
processedBins.add(processedBinsThisRun);
}
/**
* Lazily/opportunistically compress a full BIN.
*
* The target IN should be latched when we enter, and it will be remain
* latched.
*
* If compression succeeds, does not prune empty BINs, but does queue them
* for pruning later. If compression fails because a record lock cannot be
* obtained, queues the BIN to retry later.
*
* Note that we do not bother to delete queue entries for the BIN if
* compression succeeds. Queue entries are normally removed quickly by the
* compressor. In the case where queue entries happen to exist when we do
* the final compression below, we rely on the compressor to clean them up
* later on when they are processed.
*/
public void lazyCompress(final IN in, final boolean compressDirtySlots) {
assert in.isLatchOwner();
/* Only full BINs can be compressed. */
if (!in.isBIN() || in.isBINDelta()) {
return;
}
final BIN bin = (BIN) in;
/*
* Cursors prohibit compression. We queue for later when there is
* anything that can be compressed.
*/
if (bin.nCursors() > 0) {
for (int i = 0; i < bin.getNEntries(); i += 1) {
if (bin.isDefunct(i)) {
addBinToQueue(bin);
break;
}
}
return;
}
if (bin.compress(compressDirtySlots, null /*localTracker*/)) {
if (bin.getNEntries() == 0) {
/* The BIN is empty. Prune it later. */
addBinToQueue(bin);
}
} else {
/* A record lock prevented slot removal. Try again later. */
addBinToQueue(bin);
}
lazyProcessed++;
}
/*
* Find the db and bin for a BINReference.
* @return true if the db is open and the target bin is found.
*/
private boolean findDBAndBIN(
BINSearch binSearch,
BINReference binRef,
DbTree dbTree,
Map dbCache)
throws DatabaseException {
/*
* Find the database. Do not call releaseDb after this getDb, since
* the entire dbCache will be released later.
*/
binSearch.db = dbTree.getDb(
binRef.getDatabaseId(), lockTimeout, dbCache);
if (binSearch.db == null || binSearch.db.isDeleting()) {
/* The db was deleted. Ignore this BIN Ref. */
dbClosedBinsThisRun++;
return false;
}
/* Perform eviction before each operation. */
envImpl.daemonEviction(true /*backgroundIO*/);
/* Find the BIN. */
binSearch.bin = searchForBIN(binSearch.db, binRef);
if (binSearch.bin == null ||
binSearch.bin.getNodeId() != binRef.getNodeId()) {
/* The BIN may have been split. */
if (binSearch.bin != null) {
binSearch.bin.releaseLatch();
}
splitBinsThisRun++;
return false;
}
return true;
}
/* Struct to return multiple values from findDBAndBIN. */
private static class BINSearch {
public DatabaseImpl db;
public BIN bin;
}
}
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