PackWriterBitmapPreparer.java
/*
* Copyright (C) 2012, Google Inc. and others
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0 which is available at
* https://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.eclipse.jgit.internal.storage.pack;
import static org.eclipse.jgit.internal.storage.file.PackBitmapIndex.FLAG_REUSE;
import static org.eclipse.jgit.revwalk.RevFlag.SEEN;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.internal.revwalk.AddUnseenToBitmapFilter;
import org.eclipse.jgit.internal.storage.file.BitmapIndexImpl;
import org.eclipse.jgit.internal.storage.file.BitmapIndexImpl.CompressedBitmap;
import org.eclipse.jgit.internal.storage.file.PackBitmapIndex;
import org.eclipse.jgit.internal.storage.file.PackBitmapIndexBuilder;
import org.eclipse.jgit.internal.storage.file.PackBitmapIndexRemapper;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.revwalk.BitmapWalker;
import org.eclipse.jgit.revwalk.ObjectWalk;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevObject;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.revwalk.filter.RevFilter;
import org.eclipse.jgit.storage.pack.PackConfig;
import org.eclipse.jgit.util.BlockList;
import org.eclipse.jgit.util.SystemReader;
import com.googlecode.javaewah.EWAHCompressedBitmap;
/**
* Helper class for the {@link PackWriter} to select commits for which to build
* pack index bitmaps.
*/
class PackWriterBitmapPreparer {
private static final int DAY_IN_SECONDS = 24 * 60 * 60;
private static final int DISTANCE_THRESHOLD = 2000;
private static final Comparator<RevCommit> ORDER_BY_REVERSE_TIMESTAMP = (
RevCommit a, RevCommit b) -> Integer
.signum(b.getCommitTime() - a.getCommitTime());
private final ObjectReader reader;
private final ProgressMonitor pm;
private final Set<? extends ObjectId> want;
private final PackBitmapIndexBuilder writeBitmaps;
private final BitmapIndexImpl commitBitmapIndex;
private final PackBitmapIndexRemapper bitmapRemapper;
private final BitmapIndexImpl bitmapIndex;
private final int contiguousCommitCount;
private final int recentCommitCount;
private final int recentCommitSpan;
private final int distantCommitSpan;
private final int excessiveBranchCount;
private final long inactiveBranchTimestamp;
PackWriterBitmapPreparer(ObjectReader reader,
PackBitmapIndexBuilder writeBitmaps, ProgressMonitor pm,
Set<? extends ObjectId> want, PackConfig config)
throws IOException {
this.reader = reader;
this.writeBitmaps = writeBitmaps;
this.pm = pm;
this.want = want;
this.commitBitmapIndex = new BitmapIndexImpl(writeBitmaps);
this.bitmapRemapper = PackBitmapIndexRemapper.newPackBitmapIndex(
reader.getBitmapIndex(), writeBitmaps);
this.bitmapIndex = new BitmapIndexImpl(bitmapRemapper);
this.contiguousCommitCount = config.getBitmapContiguousCommitCount();
this.recentCommitCount = config.getBitmapRecentCommitCount();
this.recentCommitSpan = config.getBitmapRecentCommitSpan();
this.distantCommitSpan = config.getBitmapDistantCommitSpan();
this.excessiveBranchCount = config.getBitmapExcessiveBranchCount();
long now = SystemReader.getInstance().getCurrentTime();
long ageInSeconds = config.getBitmapInactiveBranchAgeInDays()
* DAY_IN_SECONDS;
this.inactiveBranchTimestamp = (now / 1000) - ageInSeconds;
}
/**
* Returns the commit objects for which bitmap indices should be built.
*
* @param expectedCommitCount
* count of commits in the pack
* @param excludeFromBitmapSelection
* commits that should be excluded from bitmap selection
* @return commit objects for which bitmap indices should be built
* @throws IncorrectObjectTypeException
* if any of the processed objects is not a commit
* @throws IOException
* on errors reading pack or index files
* @throws MissingObjectException
* if an expected object is missing
*/
Collection<BitmapCommit> selectCommits(int expectedCommitCount,
Set<? extends ObjectId> excludeFromBitmapSelection)
throws IncorrectObjectTypeException, IOException,
MissingObjectException {
/*
* Thinking of bitmap indices as a cache, if we find bitmaps at or at a
* close ancestor to 'old' and 'new' when calculating old..new, then all
* objects can be calculated with minimal graph walking. A distribution
* that favors creating bitmaps for the most recent commits maximizes
* the cache hits for clients that are close to HEAD, which is the
* majority of calculations performed.
*/
try (RevWalk rw = new RevWalk(reader);
RevWalk rw2 = new RevWalk(reader)) {
pm.beginTask(JGitText.get().selectingCommits,
ProgressMonitor.UNKNOWN);
rw.setRetainBody(false);
CommitSelectionHelper selectionHelper = captureOldAndNewCommits(rw,
expectedCommitCount, excludeFromBitmapSelection);
pm.endTask();
// Add reused bitmaps from the previous GC pack's bitmap indices.
// Currently they are always fully reused, even if their spans don't
// match this run's PackConfig values.
int newCommits = selectionHelper.getCommitCount();
BlockList<BitmapCommit> selections = new BlockList<>(
selectionHelper.reusedCommits.size()
+ newCommits / recentCommitSpan + 1);
for (BitmapCommit reuse : selectionHelper.reusedCommits) {
selections.add(reuse);
}
if (newCommits == 0) {
for (AnyObjectId id : selectionHelper.newWants) {
selections.add(new BitmapCommit(id, false, 0));
}
return selections;
}
pm.beginTask(JGitText.get().selectingCommits, newCommits);
int totalWants = want.size();
BitmapBuilder seen = commitBitmapIndex.newBitmapBuilder();
seen.or(selectionHelper.reusedCommitsBitmap);
rw2.setRetainBody(false);
rw2.setRevFilter(new NotInBitmapFilter(seen));
// For each branch, do a revwalk to enumerate its commits. Exclude
// both reused commits and any commits seen in a previous branch.
// Then iterate through all new commits from oldest to newest,
// selecting well-spaced commits in this branch.
for (RevCommit rc : selectionHelper.newWantsByNewest) {
BitmapBuilder tipBitmap = commitBitmapIndex.newBitmapBuilder();
rw2.markStart((RevCommit) rw2.peel(rw2.parseAny(rc)));
RevCommit rc2;
while ((rc2 = rw2.next()) != null) {
tipBitmap.addObject(rc2, Constants.OBJ_COMMIT);
}
int cardinality = tipBitmap.cardinality();
seen.or(tipBitmap);
// Within this branch, keep ordered lists of commits
// representing chains in its history, where each chain is a
// "sub-branch". Ordering commits by these chains makes for
// fewer differences between consecutive selected commits, which
// in turn provides better compression/on the run-length
// encoding of the XORs between them.
List<List<BitmapCommit>> chains = new ArrayList<>();
// Mark the current branch as inactive if its tip commit isn't
// recent and there are an excessive number of branches, to
// prevent memory bloat of computing too many bitmaps for stale
// branches.
boolean isActiveBranch = true;
if (totalWants > excessiveBranchCount && !isRecentCommit(rc)) {
isActiveBranch = false;
}
// Insert bitmaps at the offsets suggested by the
// nextSelectionDistance() heuristic. Only reuse bitmaps created
// for more distant commits.
int index = -1;
int nextIn = nextSpan(cardinality);
int nextFlg = nextIn == distantCommitSpan
? PackBitmapIndex.FLAG_REUSE
: 0;
// For the current branch, iterate through all commits from
// oldest to newest.
for (RevCommit c : selectionHelper) {
// Optimization: if we have found all the commits for this
// branch, stop searching
int distanceFromTip = cardinality - index - 1;
if (distanceFromTip == 0) {
break;
}
// Ignore commits that are not in this branch
if (!tipBitmap.contains(c)) {
continue;
}
index++;
nextIn--;
pm.update(1);
// Always pick the items in wants, prefer merge commits.
if (selectionHelper.newWants.remove(c)) {
if (nextIn > 0) {
nextFlg = 0;
}
} else {
boolean stillInSpan = nextIn >= 0;
boolean isMergeCommit = c.getParentCount() > 1;
// Force selection if:
// a) we have exhausted the window looking for merges
// b) we are in the top commits of an active branch
// c) we are at a branch tip
boolean mustPick = (nextIn <= -recentCommitSpan)
|| (isActiveBranch
&& (distanceFromTip <= contiguousCommitCount))
|| (distanceFromTip == 1); // most recent commit
if (!mustPick && (stillInSpan || !isMergeCommit)) {
continue;
}
}
// This commit is selected.
// Calculate where to look for the next one.
int flags = nextFlg;
int currDist = distanceFromTip;
nextIn = nextSpan(distanceFromTip);
nextFlg = nextIn == distantCommitSpan
? PackBitmapIndex.FLAG_REUSE
: 0;
// Create the commit bitmap for the current commit
BitmapBuilder bitmap = commitBitmapIndex.newBitmapBuilder();
rw.reset();
rw.markStart(c);
rw.setRevFilter(new AddUnseenToBitmapFilter(
selectionHelper.reusedCommitsBitmap, bitmap));
while (rw.next() != null) {
// The filter adds the reachable commits to bitmap.
}
// Sort the commits by independent chains in this branch's
// history, yielding better compression when building
// bitmaps.
List<BitmapCommit> longestAncestorChain = null;
for (List<BitmapCommit> chain : chains) {
BitmapCommit mostRecentCommit = chain
.get(chain.size() - 1);
if (bitmap.contains(mostRecentCommit)) {
if (longestAncestorChain == null
|| longestAncestorChain.size() < chain
.size()) {
longestAncestorChain = chain;
}
}
}
if (longestAncestorChain == null) {
longestAncestorChain = new ArrayList<>();
chains.add(longestAncestorChain);
}
// The commit bc should reuse bitmap walker from its close
// ancestor. And the bitmap of bc should only be added to
// PackBitmapIndexBuilder when it's an old enough
// commit,i.e. distance from tip should be greater than
// DISTANCE_THRESHOLD, to save memory.
BitmapCommit bc = BitmapCommit.newBuilder(c).setFlags(flags)
.setAddToIndex(currDist >= DISTANCE_THRESHOLD)
.setReuseWalker(!longestAncestorChain.isEmpty())
.build();
longestAncestorChain.add(bc);
writeBitmaps.addBitmap(c, bitmap, 0);
}
for (List<BitmapCommit> chain : chains) {
selections.addAll(chain);
}
}
// Add the remaining peeledWant
for (AnyObjectId remainingWant : selectionHelper.newWants) {
selections.add(new BitmapCommit(remainingWant, false, 0));
}
writeBitmaps.resetBitmaps(selections.size()); // Remove the temporary commit bitmaps.
pm.endTask();
return selections;
}
}
private boolean isRecentCommit(RevCommit revCommit) {
return revCommit.getCommitTime() > inactiveBranchTimestamp;
}
/**
* A RevFilter that excludes the commits named in a bitmap from the walk.
* <p>
* If a commit is in {@code bitmap} then that commit is not emitted by the
* walk and its parents are marked as SEEN so the walk can skip them. The
* bitmaps passed in have the property that the parents of any commit in
* {@code bitmap} are also in {@code bitmap}, so marking the parents as
* SEEN speeds up the RevWalk by saving it from walking down blind alleys
* and does not change the commits emitted.
*/
private static class NotInBitmapFilter extends RevFilter {
private final BitmapBuilder bitmap;
NotInBitmapFilter(BitmapBuilder bitmap) {
this.bitmap = bitmap;
}
@Override
public final boolean include(RevWalk rw, RevCommit c) {
if (!bitmap.contains(c)) {
return true;
}
for (RevCommit p : c.getParents()) {
p.add(SEEN);
}
return false;
}
@Override
public final NotInBitmapFilter clone() {
throw new UnsupportedOperationException();
}
@Override
public final boolean requiresCommitBody() {
return false;
}
}
/**
* Records which of the {@code wants} can be found in the previous GC pack's
* bitmap indices and which are new.
*
* @param rw
* a {@link RevWalk} to find reachable objects in this repository
* @param expectedCommitCount
* expected count of commits. The actual count may be less due to
* unreachable garbage.
* @param excludeFromBitmapSelection
* commits that should be excluded from bitmap selection
* @return a {@link CommitSelectionHelper} capturing which commits are
* covered by a previous pack's bitmaps and which new commits need
* bitmap coverage
* @throws IncorrectObjectTypeException
* if any of the processed objects is not a commit
* @throws IOException
* on errors reading pack or index files
* @throws MissingObjectException
* if an expected object is missing
*/
private CommitSelectionHelper captureOldAndNewCommits(RevWalk rw,
int expectedCommitCount,
Set<? extends ObjectId> excludeFromBitmapSelection)
throws IncorrectObjectTypeException, IOException,
MissingObjectException {
// Track bitmaps and commits from the previous GC pack bitmap indices.
BitmapBuilder reuse = commitBitmapIndex.newBitmapBuilder();
List<BitmapCommit> reuseCommits = new ArrayList<>();
for (PackBitmapIndexRemapper.Entry entry : bitmapRemapper) {
// More recent commits did not have the reuse flag set, so skip them
if ((entry.getFlags() & FLAG_REUSE) != FLAG_REUSE) {
continue;
}
RevObject ro = rw.peel(rw.parseAny(entry));
if (!(ro instanceof RevCommit)) {
continue;
}
RevCommit rc = (RevCommit) ro;
reuseCommits.add(new BitmapCommit(rc, false, entry.getFlags()));
if (!reuse.contains(rc)) {
EWAHCompressedBitmap bitmap = bitmapRemapper.ofObjectType(
bitmapRemapper.getBitmap(rc), Constants.OBJ_COMMIT);
reuse.or(new CompressedBitmap(bitmap, commitBitmapIndex));
}
}
// Add branch tips that are not represented in a previous pack's bitmap
// indices. Set up a RevWalk to find new commits not in the old packs.
List<RevCommit> newWantsByNewest = new ArrayList<>(want.size());
Set<RevCommit> newWants = new HashSet<>(want.size());
for (AnyObjectId objectId : want) {
RevObject ro = rw.peel(rw.parseAny(objectId));
if (!(ro instanceof RevCommit) || reuse.contains(ro)
|| excludeFromBitmapSelection.contains(ro)) {
continue;
}
RevCommit rc = (RevCommit) ro;
rw.markStart(rc);
newWants.add(rc);
newWantsByNewest.add(rc);
}
// Create a list of commits in reverse order (older to newer) that are
// not in the previous bitmap indices and are reachable.
rw.setRevFilter(new NotInBitmapFilter(reuse));
RevCommit[] commits = new RevCommit[expectedCommitCount];
int pos = commits.length;
RevCommit rc;
while ((rc = rw.next()) != null && pos > 0) {
commits[--pos] = rc;
pm.update(1);
}
// Sort the new wants by reverse commit time.
Collections.sort(newWantsByNewest, ORDER_BY_REVERSE_TIMESTAMP);
return new CommitSelectionHelper(newWants, commits, pos,
newWantsByNewest, reuse, reuseCommits);
}
/*-
* Returns the desired distance to the next bitmap based on the distance
* from the tip commit. Only differentiates recent from distant spans,
* selectCommits() handles the contiguous commits at the tip for active
* or inactive branches.
*
* A graph of this function looks like this, where
* the X axis is the distance from the tip commit and the Y axis is the
* bitmap selection distance.
*
* 5000 ____...
* /
* /
* /
* /
* 100 _____/
* 0 20100 25000
*
* Linear scaling between 20100 and 25000 prevents spans >100 for distances
* <20000 (otherwise, a span of 5000 would be returned for a distance of
* 21000, and the range 16000-20000 would have no selections).
*/
int nextSpan(int distanceFromTip) {
if (distanceFromTip < 0) {
throw new IllegalArgumentException();
}
// Commits more toward the start will have more bitmaps.
if (distanceFromTip <= recentCommitCount) {
return recentCommitSpan;
}
int next = Math.min(distanceFromTip - recentCommitCount,
distantCommitSpan);
return Math.max(next, recentCommitSpan);
}
BitmapWalker newBitmapWalker() {
return new BitmapWalker(
new ObjectWalk(reader), bitmapIndex, null);
}
/**
* Container for state used in the first phase of selecting commits, which
* walks all of the reachable commits via the branch tips that are not
* covered by a previous pack's bitmaps ({@code newWants}) and stores them
* in {@code newCommitsByOldest}. {@code newCommitsByOldest} is initialized
* with an expected size of all commits, but may be smaller if some commits
* are unreachable and/or some commits are covered by a previous pack's
* bitmaps. {@code commitStartPos} will contain a positive offset to either
* the root commit or the oldest commit not covered by previous bitmaps.
*/
private static final class CommitSelectionHelper implements Iterable<RevCommit> {
final Set<? extends ObjectId> newWants;
final List<RevCommit> newWantsByNewest;
final BitmapBuilder reusedCommitsBitmap;
final List<BitmapCommit> reusedCommits;
final RevCommit[] newCommitsByOldest;
final int newCommitStartPos;
CommitSelectionHelper(Set<? extends ObjectId> newWants,
RevCommit[] commitsByOldest, int commitStartPos,
List<RevCommit> newWantsByNewest,
BitmapBuilder reusedCommitsBitmap,
List<BitmapCommit> reuse) {
this.newWants = newWants;
this.newCommitsByOldest = commitsByOldest;
this.newCommitStartPos = commitStartPos;
this.newWantsByNewest = newWantsByNewest;
this.reusedCommitsBitmap = reusedCommitsBitmap;
this.reusedCommits = reuse;
}
@Override
public Iterator<RevCommit> iterator() {
// Member variables referenced by this iterator will have synthetic
// accessors generated for them if they are made private.
return new Iterator<>() {
int pos = newCommitStartPos;
@Override
public boolean hasNext() {
return pos < newCommitsByOldest.length;
}
@Override
public RevCommit next() {
return newCommitsByOldest[pos++];
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
int getCommitCount() {
return newCommitsByOldest.length - newCommitStartPos;
}
}
}