PackConfig.java

/*
 * Copyright (C) 2008-2010, Google Inc.
 * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com> 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.storage.pack;

import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_CORE_SECTION;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BIGFILE_THRESHOLD;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BITMAP_CONTIGUOUS_COMMIT_COUNT;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BITMAP_DISTANT_COMMIT_SPAN;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BITMAP_EXCESSIVE_BRANCH_COUNT;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BITMAP_INACTIVE_BRANCH_AGE_INDAYS;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BITMAP_RECENT_COMMIT_COUNT;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_BUILD_BITMAPS;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_COMPRESSION;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_CUT_DELTACHAINS;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_DELTA_CACHE_LIMIT;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_DELTA_CACHE_SIZE;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_DELTA_COMPRESSION;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_DEPTH;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_INDEXVERSION;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_MIN_SIZE_PREVENT_RACYPACK;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_REUSE_DELTAS;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_REUSE_OBJECTS;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_SEARCH_FOR_REUSE_TIMEOUT;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_SINGLE_PACK;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_THREADS;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_WAIT_PREVENT_RACYPACK;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_WINDOW;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_WINDOW_MEMORY;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_PACK_SECTION;

import java.time.Duration;
import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;
import java.util.zip.Deflater;

import org.eclipse.jgit.internal.storage.file.PackIndexWriter;
import org.eclipse.jgit.lib.Config;
import org.eclipse.jgit.lib.Repository;

/**
 * Configuration used by a pack writer when constructing the stream.
 *
 * A configuration may be modified once created, but should not be modified
 * while it is being used by a PackWriter. If a configuration is not modified it
 * is safe to share the same configuration instance between multiple concurrent
 * threads executing different PackWriters.
 */
public class PackConfig {
    /**
     * Default value of deltas reuse option: {@value}
     *
     * @see #setReuseDeltas(boolean)
     */
    public static final boolean DEFAULT_REUSE_DELTAS = true;

    /**
     * Default value of objects reuse option: {@value}
     *
     * @see #setReuseObjects(boolean)
     */
    public static final boolean DEFAULT_REUSE_OBJECTS = true;

    /**
     * Default value of keep old packs option: {@value}
     * @see #setPreserveOldPacks(boolean)
     * @since 4.7
     */
    public static final boolean DEFAULT_PRESERVE_OLD_PACKS = false;

    /**
     * Default value of prune old packs option: {@value}
     * @see #setPrunePreserved(boolean)
     * @since 4.7
     */
    public static final boolean DEFAULT_PRUNE_PRESERVED = false;

    /**
     * Default value of delta compress option: {@value}
     *
     * @see #setDeltaCompress(boolean)
     */
    public static final boolean DEFAULT_DELTA_COMPRESS = true;

    /**
     * Default value of delta base as offset option: {@value}
     *
     * @see #setDeltaBaseAsOffset(boolean)
     */
    public static final boolean DEFAULT_DELTA_BASE_AS_OFFSET = false;

    /**
     * Default value of maximum delta chain depth: {@value}
     *
     * @see #setMaxDeltaDepth(int)
     */
    public static final int DEFAULT_MAX_DELTA_DEPTH = 50;

    /**
     * Default window size during packing: {@value}
     *
     * @see #setDeltaSearchWindowSize(int)
     */
    public static final int DEFAULT_DELTA_SEARCH_WINDOW_SIZE = 10;

    private static final int MB = 1 << 20;

    /**
     * Default big file threshold: {@value}
     *
     * @see #setBigFileThreshold(int)
     */
    public static final int DEFAULT_BIG_FILE_THRESHOLD = 50 * MB;

    /**
     * Default if we wait before opening a newly written pack to prevent its
     * lastModified timestamp could be racy
     *
     * @since 5.1.8
     */
    public static final boolean DEFAULT_WAIT_PREVENT_RACY_PACK = false;

    /**
     * Default if we wait before opening a newly written pack to prevent its
     * lastModified timestamp could be racy
     *
     * @since 5.1.8
     */
    public static final long DEFAULT_MINSIZE_PREVENT_RACY_PACK = 100 * MB;

    /**
     * Default delta cache size: {@value}
     *
     * @see #setDeltaCacheSize(long)
     */
    public static final long DEFAULT_DELTA_CACHE_SIZE = 50 * 1024 * 1024;

    /**
     * Default delta cache limit: {@value}
     *
     * @see #setDeltaCacheLimit(int)
     */
    public static final int DEFAULT_DELTA_CACHE_LIMIT = 100;

    /**
     * Default index version: {@value}
     *
     * @see #setIndexVersion(int)
     */
    public static final int DEFAULT_INDEX_VERSION = 2;

    /**
     * Default value of the build bitmaps option: {@value}
     *
     * @see #setBuildBitmaps(boolean)
     * @since 3.0
     */
    public static final boolean DEFAULT_BUILD_BITMAPS = true;

    /**
     * Default count of most recent commits to select for bitmaps. Only applies
     * when bitmaps are enabled: {@value}
     *
     * @see #setBitmapContiguousCommitCount(int)
     * @since 4.2
     */
    public static final int DEFAULT_BITMAP_CONTIGUOUS_COMMIT_COUNT = 100;

    /**
     * Count at which the span between selected commits changes from
     * "bitmapRecentCommitSpan" to "bitmapDistantCommitSpan". Only applies when
     * bitmaps are enabled: {@value}
     *
     * @see #setBitmapRecentCommitCount(int)
     * @since 4.2
     */
    public static final int DEFAULT_BITMAP_RECENT_COMMIT_COUNT = 20000;

    /**
     * Default spacing between commits in recent history when selecting commits
     * for bitmaps. Only applies when bitmaps are enabled: {@value}
     *
     * @see #setBitmapRecentCommitSpan(int)
     * @since 4.2
     */
    public static final int DEFAULT_BITMAP_RECENT_COMMIT_SPAN = 100;

    /**
     * Default spacing between commits in distant history when selecting commits
     * for bitmaps. Only applies when bitmaps are enabled: {@value}
     *
     * @see #setBitmapDistantCommitSpan(int)
     * @since 4.2
     */
    public static final int DEFAULT_BITMAP_DISTANT_COMMIT_SPAN = 5000;

    /**
     * Default count of branches required to activate inactive branch commit
     * selection. If the number of branches is less than this then bitmaps for
     * the entire commit history of all branches will be created, otherwise
     * branches marked as "inactive" will have coverage for only partial
     * history: {@value}
     *
     * @see #setBitmapExcessiveBranchCount(int)
     * @since 4.2
     */
    public static final int DEFAULT_BITMAP_EXCESSIVE_BRANCH_COUNT = 100;

    /**
     * Default age at which a branch is considered inactive. Age is taken as the
     * number of days ago that the most recent commit was made to a branch. Only
     * affects bitmap processing if bitmaps are enabled and the
     * "excessive branch count" has been exceeded: {@value}
     *
     * @see #setBitmapInactiveBranchAgeInDays(int)
     * @since 4.2
     */
    public static final int DEFAULT_BITMAP_INACTIVE_BRANCH_AGE_IN_DAYS = 90;

    /**
     * Default max time to spend during the search for reuse phase. This
     * optimization is disabled by default: {@value}
     *
     * @see #setSearchForReuseTimeout(Duration)
     * @since 5.13
     */
    public static final Duration DEFAULT_SEARCH_FOR_REUSE_TIMEOUT = Duration
            .ofSeconds(Integer.MAX_VALUE);

    private int compressionLevel = Deflater.DEFAULT_COMPRESSION;

    private boolean reuseDeltas = DEFAULT_REUSE_DELTAS;

    private boolean reuseObjects = DEFAULT_REUSE_OBJECTS;

    private boolean preserveOldPacks = DEFAULT_PRESERVE_OLD_PACKS;

    private boolean prunePreserved = DEFAULT_PRUNE_PRESERVED;

    private boolean deltaBaseAsOffset = DEFAULT_DELTA_BASE_AS_OFFSET;

    private boolean deltaCompress = DEFAULT_DELTA_COMPRESS;

    private int maxDeltaDepth = DEFAULT_MAX_DELTA_DEPTH;

    private int deltaSearchWindowSize = DEFAULT_DELTA_SEARCH_WINDOW_SIZE;

    private long deltaSearchMemoryLimit;

    private long deltaCacheSize = DEFAULT_DELTA_CACHE_SIZE;

    private int deltaCacheLimit = DEFAULT_DELTA_CACHE_LIMIT;

    private int bigFileThreshold = DEFAULT_BIG_FILE_THRESHOLD;

    private boolean waitPreventRacyPack = DEFAULT_WAIT_PREVENT_RACY_PACK;

    private long minSizePreventRacyPack = DEFAULT_MINSIZE_PREVENT_RACY_PACK;

    private int threads;

    private Executor executor;

    private int indexVersion = DEFAULT_INDEX_VERSION;

    private boolean buildBitmaps = DEFAULT_BUILD_BITMAPS;

    private int bitmapContiguousCommitCount = DEFAULT_BITMAP_CONTIGUOUS_COMMIT_COUNT;

    private int bitmapRecentCommitCount = DEFAULT_BITMAP_RECENT_COMMIT_COUNT;

    private int bitmapRecentCommitSpan = DEFAULT_BITMAP_RECENT_COMMIT_SPAN;

    private int bitmapDistantCommitSpan = DEFAULT_BITMAP_DISTANT_COMMIT_SPAN;

    private int bitmapExcessiveBranchCount = DEFAULT_BITMAP_EXCESSIVE_BRANCH_COUNT;

    private int bitmapInactiveBranchAgeInDays = DEFAULT_BITMAP_INACTIVE_BRANCH_AGE_IN_DAYS;

    private Duration searchForReuseTimeout = DEFAULT_SEARCH_FOR_REUSE_TIMEOUT;

    private boolean cutDeltaChains;

    private boolean singlePack;

    /**
     * Create a default configuration.
     */
    public PackConfig() {
        // Fields are initialized to defaults.
    }

    /**
     * Create a configuration honoring the repository's settings.
     *
     * @param db
     *            the repository to read settings from. The repository is not
     *            retained by the new configuration, instead its settings are
     *            copied during the constructor.
     */
    public PackConfig(Repository db) {
        fromConfig(db.getConfig());
    }

    /**
     * Create a configuration honoring settings in a
     * {@link org.eclipse.jgit.lib.Config}.
     *
     * @param cfg
     *            the source to read settings from. The source is not retained
     *            by the new configuration, instead its settings are copied
     *            during the constructor.
     */
    public PackConfig(Config cfg) {
        fromConfig(cfg);
    }

    /**
     * Copy an existing configuration to a new instance.
     *
     * @param cfg
     *            the source configuration to copy from.
     */
    public PackConfig(PackConfig cfg) {
        this.compressionLevel = cfg.compressionLevel;
        this.reuseDeltas = cfg.reuseDeltas;
        this.reuseObjects = cfg.reuseObjects;
        this.preserveOldPacks = cfg.preserveOldPacks;
        this.prunePreserved = cfg.prunePreserved;
        this.deltaBaseAsOffset = cfg.deltaBaseAsOffset;
        this.deltaCompress = cfg.deltaCompress;
        this.maxDeltaDepth = cfg.maxDeltaDepth;
        this.deltaSearchWindowSize = cfg.deltaSearchWindowSize;
        this.deltaSearchMemoryLimit = cfg.deltaSearchMemoryLimit;
        this.deltaCacheSize = cfg.deltaCacheSize;
        this.deltaCacheLimit = cfg.deltaCacheLimit;
        this.bigFileThreshold = cfg.bigFileThreshold;
        this.waitPreventRacyPack = cfg.waitPreventRacyPack;
        this.minSizePreventRacyPack = cfg.minSizePreventRacyPack;
        this.threads = cfg.threads;
        this.executor = cfg.executor;
        this.indexVersion = cfg.indexVersion;
        this.buildBitmaps = cfg.buildBitmaps;
        this.bitmapContiguousCommitCount = cfg.bitmapContiguousCommitCount;
        this.bitmapRecentCommitCount = cfg.bitmapRecentCommitCount;
        this.bitmapRecentCommitSpan = cfg.bitmapRecentCommitSpan;
        this.bitmapDistantCommitSpan = cfg.bitmapDistantCommitSpan;
        this.bitmapExcessiveBranchCount = cfg.bitmapExcessiveBranchCount;
        this.bitmapInactiveBranchAgeInDays = cfg.bitmapInactiveBranchAgeInDays;
        this.cutDeltaChains = cfg.cutDeltaChains;
        this.singlePack = cfg.singlePack;
        this.searchForReuseTimeout = cfg.searchForReuseTimeout;
    }

    /**
     * Check whether to reuse deltas existing in repository.
     *
     * Default setting: {@value #DEFAULT_REUSE_DELTAS}
     *
     * @return true if object is configured to reuse deltas; false otherwise.
     */
    public boolean isReuseDeltas() {
        return reuseDeltas;
    }

    /**
     * Set reuse deltas configuration option for the writer.
     *
     * When enabled, writer will search for delta representation of object in
     * repository and use it if possible. Normally, only deltas with base to
     * another object existing in set of objects to pack will be used. The
     * exception however is thin-packs where the base object may exist on the
     * other side.
     *
     * When raw delta data is directly copied from a pack file, its checksum is
     * computed to verify the data is not corrupt.
     *
     * Default setting: {@value #DEFAULT_REUSE_DELTAS}
     *
     * @param reuseDeltas
     *            boolean indicating whether or not try to reuse deltas.
     */
    public void setReuseDeltas(boolean reuseDeltas) {
        this.reuseDeltas = reuseDeltas;
    }

    /**
     * Checks whether to reuse existing objects representation in repository.
     *
     * Default setting: {@value #DEFAULT_REUSE_OBJECTS}
     *
     * @return true if writer is configured to reuse objects representation from
     *         pack; false otherwise.
     */
    public boolean isReuseObjects() {
        return reuseObjects;
    }

    /**
     * Set reuse objects configuration option for the writer.
     *
     * If enabled, writer searches for compressed representation in a pack file.
     * If possible, compressed data is directly copied from such a pack file.
     * Data checksum is verified.
     *
     * Default setting: {@value #DEFAULT_REUSE_OBJECTS}
     *
     * @param reuseObjects
     *            boolean indicating whether or not writer should reuse existing
     *            objects representation.
     */
    public void setReuseObjects(boolean reuseObjects) {
        this.reuseObjects = reuseObjects;
    }

    /**
     * Checks whether to preserve old packs in a preserved directory
     *
     * Default setting: {@value #DEFAULT_PRESERVE_OLD_PACKS}
     *
     * @return true if repacking will preserve old pack files.
     * @since 4.7
     */
    public boolean isPreserveOldPacks() {
        return preserveOldPacks;
    }

    /**
     * Set preserve old packs configuration option for repacking.
     *
     * If enabled, old pack files are moved into a preserved subdirectory instead
     * of being deleted
     *
     * Default setting: {@value #DEFAULT_PRESERVE_OLD_PACKS}
     *
     * @param preserveOldPacks
     *            boolean indicating whether or not preserve old pack files
     * @since 4.7
     */
    public void setPreserveOldPacks(boolean preserveOldPacks) {
        this.preserveOldPacks = preserveOldPacks;
    }

    /**
     * Checks whether to remove preserved pack files in a preserved directory
     *
     * Default setting: {@value #DEFAULT_PRUNE_PRESERVED}
     *
     * @return true if repacking will remove preserved pack files.
     * @since 4.7
     */
    public boolean isPrunePreserved() {
        return prunePreserved;
    }

    /**
     * Set prune preserved configuration option for repacking.
     *
     * If enabled, preserved pack files are removed from a preserved subdirectory
     *
     * Default setting: {@value #DEFAULT_PRESERVE_OLD_PACKS}
     *
     * @param prunePreserved
     *            boolean indicating whether or not preserve old pack files
     * @since 4.7
     */
    public void setPrunePreserved(boolean prunePreserved) {
        this.prunePreserved = prunePreserved;
    }

    /**
     * True if writer can use offsets to point to a delta base.
     *
     * If true the writer may choose to use an offset to point to a delta base
     * in the same pack, this is a newer style of reference that saves space.
     * False if the writer has to use the older (and more compatible style) of
     * storing the full ObjectId of the delta base.
     *
     * Default setting: {@value #DEFAULT_DELTA_BASE_AS_OFFSET}
     *
     * @return true if delta base is stored as an offset; false if it is stored
     *         as an ObjectId.
     */
    public boolean isDeltaBaseAsOffset() {
        return deltaBaseAsOffset;
    }

    /**
     * Set writer delta base format.
     *
     * Delta base can be written as an offset in a pack file (new approach
     * reducing file size) or as an object id (legacy approach, compatible with
     * old readers).
     *
     * Default setting: {@value #DEFAULT_DELTA_BASE_AS_OFFSET}
     *
     * @param deltaBaseAsOffset
     *            boolean indicating whether delta base can be stored as an
     *            offset.
     */
    public void setDeltaBaseAsOffset(boolean deltaBaseAsOffset) {
        this.deltaBaseAsOffset = deltaBaseAsOffset;
    }

    /**
     * Check whether the writer will create new deltas on the fly.
     *
     * Default setting: {@value #DEFAULT_DELTA_COMPRESS}
     *
     * @return true if the writer will create a new delta when either
     *         {@link #isReuseDeltas()} is false, or no suitable delta is
     *         available for reuse.
     */
    public boolean isDeltaCompress() {
        return deltaCompress;
    }

    /**
     * Set whether or not the writer will create new deltas on the fly.
     *
     * Default setting: {@value #DEFAULT_DELTA_COMPRESS}
     *
     * @param deltaCompress
     *            true to create deltas when {@link #isReuseDeltas()} is false,
     *            or when a suitable delta isn't available for reuse. Set to
     *            false to write whole objects instead.
     */
    public void setDeltaCompress(boolean deltaCompress) {
        this.deltaCompress = deltaCompress;
    }

    /**
     * Get maximum depth of delta chain set up for the writer.
     *
     * Generated chains are not longer than this value.
     *
     * Default setting: {@value #DEFAULT_MAX_DELTA_DEPTH}
     *
     * @return maximum delta chain depth.
     */
    public int getMaxDeltaDepth() {
        return maxDeltaDepth;
    }

    /**
     * Set up maximum depth of delta chain for the writer.
     *
     * Generated chains are not longer than this value. Too low value causes low
     * compression level, while too big makes unpacking (reading) longer.
     *
     * Default setting: {@value #DEFAULT_MAX_DELTA_DEPTH}
     *
     * @param maxDeltaDepth
     *            maximum delta chain depth.
     */
    public void setMaxDeltaDepth(int maxDeltaDepth) {
        this.maxDeltaDepth = maxDeltaDepth;
    }

    /**
     * Whether existing delta chains should be cut at
     * {@link #getMaxDeltaDepth()}.
     *
     * @return true if existing delta chains should be cut at
     *         {@link #getMaxDeltaDepth()}. Default is false, allowing existing
     *         chains to be of any length.
     * @since 3.0
     */
    public boolean getCutDeltaChains() {
        return cutDeltaChains;
    }

    /**
     * Enable cutting existing delta chains at {@link #getMaxDeltaDepth()}.
     *
     * By default this is disabled and existing chains are kept at whatever
     * length a prior packer was configured to create. This allows objects to be
     * packed one with a large depth (for example 250), and later to quickly
     * repack the repository with a shorter depth (such as 50), but reusing the
     * complete delta chains created by the earlier 250 depth.
     *
     * @param cut
     *            true to cut existing chains.
     * @since 3.0
     */
    public void setCutDeltaChains(boolean cut) {
        cutDeltaChains = cut;
    }

    /**
     * Whether all of refs/* should be packed in a single pack.
     *
     * @return true if all of refs/* should be packed in a single pack. Default
     *         is false, packing a separate GC_REST pack for references outside
     *         of refs/heads/* and refs/tags/*.
     * @since 4.9
     */
    public boolean getSinglePack() {
        return singlePack;
    }

    /**
     * If {@code true}, packs a single GC pack for all objects reachable from
     * refs/*. Otherwise packs the GC pack with objects reachable from
     * refs/heads/* and refs/tags/*, and a GC_REST pack with the remaining
     * reachable objects. Disabled by default, packing GC and GC_REST.
     *
     * @param single
     *            true to pack a single GC pack rather than GC and GC_REST packs
     * @since 4.9
     */
    public void setSinglePack(boolean single) {
        singlePack = single;
    }

    /**
     * Get the number of objects to try when looking for a delta base.
     *
     * This limit is per thread, if 4 threads are used the actual memory used
     * will be 4 times this value.
     *
     * Default setting: {@value #DEFAULT_DELTA_SEARCH_WINDOW_SIZE}
     *
     * @return the object count to be searched.
     */
    public int getDeltaSearchWindowSize() {
        return deltaSearchWindowSize;
    }

    /**
     * Set the number of objects considered when searching for a delta base.
     *
     * Default setting: {@value #DEFAULT_DELTA_SEARCH_WINDOW_SIZE}
     *
     * @param objectCount
     *            number of objects to search at once. Must be at least 2.
     */
    public void setDeltaSearchWindowSize(int objectCount) {
        if (objectCount <= 2)
            setDeltaCompress(false);
        else
            deltaSearchWindowSize = objectCount;
    }

    /**
     * Get maximum number of bytes to put into the delta search window.
     *
     * Default setting is 0, for an unlimited amount of memory usage. Actual
     * memory used is the lower limit of either this setting, or the sum of
     * space used by at most {@link #getDeltaSearchWindowSize()} objects.
     *
     * This limit is per thread, if 4 threads are used the actual memory limit
     * will be 4 times this value.
     *
     * @return the memory limit.
     */
    public long getDeltaSearchMemoryLimit() {
        return deltaSearchMemoryLimit;
    }

    /**
     * Set the maximum number of bytes to put into the delta search window.
     *
     * Default setting is 0, for an unlimited amount of memory usage. If the
     * memory limit is reached before {@link #getDeltaSearchWindowSize()} the
     * window size is temporarily lowered.
     *
     * @param memoryLimit
     *            Maximum number of bytes to load at once, 0 for unlimited.
     */
    public void setDeltaSearchMemoryLimit(long memoryLimit) {
        deltaSearchMemoryLimit = memoryLimit;
    }

    /**
     * Get the size of the in-memory delta cache.
     *
     * This limit is for the entire writer, even if multiple threads are used.
     *
     * Default setting: {@value #DEFAULT_DELTA_CACHE_SIZE}
     *
     * @return maximum number of bytes worth of delta data to cache in memory.
     *         If 0 the cache is infinite in size (up to the JVM heap limit
     *         anyway). A very tiny size such as 1 indicates the cache is
     *         effectively disabled.
     */
    public long getDeltaCacheSize() {
        return deltaCacheSize;
    }

    /**
     * Set the maximum number of bytes of delta data to cache.
     *
     * During delta search, up to this many bytes worth of small or hard to
     * compute deltas will be stored in memory. This cache speeds up writing by
     * allowing the cached entry to simply be dumped to the output stream.
     *
     * Default setting: {@value #DEFAULT_DELTA_CACHE_SIZE}
     *
     * @param size
     *            number of bytes to cache. Set to 0 to enable an infinite
     *            cache, set to 1 (an impossible size for any delta) to disable
     *            the cache.
     */
    public void setDeltaCacheSize(long size) {
        deltaCacheSize = size;
    }

    /**
     * Maximum size in bytes of a delta to cache.
     *
     * Default setting: {@value #DEFAULT_DELTA_CACHE_LIMIT}
     *
     * @return maximum size (in bytes) of a delta that should be cached.
     */
    public int getDeltaCacheLimit() {
        return deltaCacheLimit;
    }

    /**
     * Set the maximum size of a delta that should be cached.
     *
     * During delta search, any delta smaller than this size will be cached, up
     * to the {@link #getDeltaCacheSize()} maximum limit. This speeds up writing
     * by allowing these cached deltas to be output as-is.
     *
     * Default setting: {@value #DEFAULT_DELTA_CACHE_LIMIT}
     *
     * @param size
     *            maximum size (in bytes) of a delta to be cached.
     */
    public void setDeltaCacheLimit(int size) {
        deltaCacheLimit = size;
    }

    /**
     * Get the maximum file size that will be delta compressed.
     *
     * Files bigger than this setting will not be delta compressed, as they are
     * more than likely already highly compressed binary data files that do not
     * delta compress well, such as MPEG videos.
     *
     * Default setting: {@value #DEFAULT_BIG_FILE_THRESHOLD}
     *
     * @return the configured big file threshold.
     */
    public int getBigFileThreshold() {
        return bigFileThreshold;
    }

    /**
     * Set the maximum file size that should be considered for deltas.
     *
     * Default setting: {@value #DEFAULT_BIG_FILE_THRESHOLD}
     *
     * @param bigFileThreshold
     *            the limit, in bytes.
     */
    public void setBigFileThreshold(int bigFileThreshold) {
        this.bigFileThreshold = bigFileThreshold;
    }

    /**
     * Get whether we wait before opening a newly written pack to prevent its
     * lastModified timestamp could be racy
     *
     * @return whether we wait before opening a newly written pack to prevent
     *         its lastModified timestamp could be racy
     * @since 5.1.8
     */
    public boolean isWaitPreventRacyPack() {
        return waitPreventRacyPack;
    }

    /**
     * Get whether we wait before opening a newly written pack to prevent its
     * lastModified timestamp could be racy. Returns {@code true} if
     * {@code waitToPreventRacyPack = true} and
     * {@code packSize > minSizePreventRacyPack}, {@code false} otherwise.
     *
     * @param packSize
     *            size of the pack file
     *
     * @return whether we wait before opening a newly written pack to prevent
     *         its lastModified timestamp could be racy
     * @since 5.1.8
     */
    public boolean doWaitPreventRacyPack(long packSize) {
        return isWaitPreventRacyPack()
                && packSize > getMinSizePreventRacyPack();
    }

    /**
     * Set whether we wait before opening a newly written pack to prevent its
     * lastModified timestamp could be racy
     *
     * @param waitPreventRacyPack
     *            whether we wait before opening a newly written pack to prevent
     *            its lastModified timestamp could be racy
     * @since 5.1.8
     */
    public void setWaitPreventRacyPack(boolean waitPreventRacyPack) {
        this.waitPreventRacyPack = waitPreventRacyPack;
    }

    /**
     * Get minimum packfile size for which we wait before opening a newly
     * written pack to prevent its lastModified timestamp could be racy if
     * {@code isWaitToPreventRacyPack} is {@code true}.
     *
     * @return minimum packfile size, default is 100 MiB
     *
     * @since 5.1.8
     */
    public long getMinSizePreventRacyPack() {
        return minSizePreventRacyPack;
    }

    /**
     * Set minimum packfile size for which we wait before opening a newly
     * written pack to prevent its lastModified timestamp could be racy if
     * {@code isWaitToPreventRacyPack} is {@code true}.
     *
     * @param minSizePreventRacyPack
     *            minimum packfile size, default is 100 MiB
     *
     * @since 5.1.8
     */
    public void setMinSizePreventRacyPack(long minSizePreventRacyPack) {
        this.minSizePreventRacyPack = minSizePreventRacyPack;
    }

    /**
     * Get the compression level applied to objects in the pack.
     *
     * Default setting: {@value java.util.zip.Deflater#DEFAULT_COMPRESSION}
     *
     * @return current compression level, see {@link java.util.zip.Deflater}.
     */
    public int getCompressionLevel() {
        return compressionLevel;
    }

    /**
     * Set the compression level applied to objects in the pack.
     *
     * Default setting: {@value java.util.zip.Deflater#DEFAULT_COMPRESSION}
     *
     * @param level
     *            compression level, must be a valid level recognized by the
     *            {@link java.util.zip.Deflater} class.
     */
    public void setCompressionLevel(int level) {
        compressionLevel = level;
    }

    /**
     * Get the number of threads used during delta compression.
     *
     * Default setting: 0 (auto-detect processors)
     *
     * @return number of threads used for delta compression. 0 will auto-detect
     *         the threads to the number of available processors.
     */
    public int getThreads() {
        return threads;
    }

    /**
     * Set the number of threads to use for delta compression.
     *
     * During delta compression, if there are enough objects to be considered
     * the writer will start up concurrent threads and allow them to compress
     * different sections of the repository concurrently.
     *
     * An application thread pool can be set by {@link #setExecutor(Executor)}.
     * If not set a temporary pool will be created by the writer, and torn down
     * automatically when compression is over.
     *
     * Default setting: 0 (auto-detect processors)
     *
     * @param threads
     *            number of threads to use. If &lt;= 0 the number of available
     *            processors for this JVM is used.
     */
    public void setThreads(int threads) {
        this.threads = threads;
    }

    /**
     * Get the preferred thread pool to execute delta search on.
     *
     * @return the preferred thread pool to execute delta search on.
     */
    public Executor getExecutor() {
        return executor;
    }

    /**
     * Set the executor to use when using threads.
     *
     * During delta compression if the executor is non-null jobs will be queued
     * up on it to perform delta compression in parallel. Aside from setting the
     * executor, the caller must set {@link #setThreads(int)} to enable threaded
     * delta search.
     *
     * @param executor
     *            executor to use for threads. Set to null to create a temporary
     *            executor just for the writer.
     */
    public void setExecutor(Executor executor) {
        this.executor = executor;
    }

    /**
     * Get the pack index file format version this instance creates.
     *
     * Default setting: {@value #DEFAULT_INDEX_VERSION}
     *
     * @return the index version, the special version 0 designates the oldest
     *         (most compatible) format available for the objects.
     * @see PackIndexWriter
     */
    public int getIndexVersion() {
        return indexVersion;
    }

    /**
     * Set the pack index file format version this instance will create.
     *
     * Default setting: {@value #DEFAULT_INDEX_VERSION}
     *
     * @param version
     *            the version to write. The special version 0 designates the
     *            oldest (most compatible) format available for the objects.
     * @see PackIndexWriter
     */
    public void setIndexVersion(int version) {
        indexVersion = version;
    }

    /**
     * True if writer is allowed to build bitmaps for indexes.
     *
     * Default setting: {@value #DEFAULT_BUILD_BITMAPS}
     *
     * @return true if delta base is the writer can choose to output an index
     *         with bitmaps.
     * @since 3.0
     */
    public boolean isBuildBitmaps() {
        return buildBitmaps;
    }

    /**
     * Set writer to allow building bitmaps for supported pack files.
     *
     * Index files can include bitmaps to speed up future ObjectWalks.
     *
     * Default setting: {@value #DEFAULT_BUILD_BITMAPS}
     *
     * @param buildBitmaps
     *            boolean indicating whether bitmaps may be included in the
     *            index.
     * @since 3.0
     */
    public void setBuildBitmaps(boolean buildBitmaps) {
        this.buildBitmaps = buildBitmaps;
    }

    /**
     * Get the count of most recent commits for which to build bitmaps.
     *
     * Default setting: {@value #DEFAULT_BITMAP_CONTIGUOUS_COMMIT_COUNT}
     *
     * @return the count of most recent commits for which to build bitmaps
     * @since 4.2
     */
    public int getBitmapContiguousCommitCount() {
        return bitmapContiguousCommitCount;
    }

    /**
     * Set the count of most recent commits for which to build bitmaps.
     *
     * Default setting: {@value #DEFAULT_BITMAP_CONTIGUOUS_COMMIT_COUNT}
     *
     * @param count
     *            the count of most recent commits for which to build bitmaps
     * @since 4.2
     */
    public void setBitmapContiguousCommitCount(int count) {
        bitmapContiguousCommitCount = count;
    }

    /**
     * Get the count at which to switch from "bitmapRecentCommitSpan" to
     * "bitmapDistantCommitSpan".
     *
     * Default setting: {@value #DEFAULT_BITMAP_RECENT_COMMIT_COUNT}
     *
     * @return the count for switching between recent and distant spans
     * @since 4.2
     */
    public int getBitmapRecentCommitCount() {
        return bitmapRecentCommitCount;
    }

    /**
     * Set the count at which to switch from "bitmapRecentCommitSpan" to
     * "bitmapDistantCommitSpan".
     *
     * Default setting: {@value #DEFAULT_BITMAP_RECENT_COMMIT_COUNT}
     *
     * @param count
     *            the count for switching between recent and distant spans
     * @since 4.2
     */
    public void setBitmapRecentCommitCount(int count) {
        bitmapRecentCommitCount = count;
    }

    /**
     * Get the span of commits when building bitmaps for recent history.
     *
     * Default setting: {@value #DEFAULT_BITMAP_RECENT_COMMIT_SPAN}
     *
     * @return the span of commits when building bitmaps for recent history
     * @since 4.2
     */
    public int getBitmapRecentCommitSpan() {
        return bitmapRecentCommitSpan;
    }

    /**
     * Set the span of commits when building bitmaps for recent history.
     *
     * Default setting: {@value #DEFAULT_BITMAP_RECENT_COMMIT_SPAN}
     *
     * @param span
     *            the span of commits when building bitmaps for recent history
     * @since 4.2
     */
    public void setBitmapRecentCommitSpan(int span) {
        bitmapRecentCommitSpan = span;
    }

    /**
     * Get the span of commits when building bitmaps for distant history.
     *
     * Default setting: {@value #DEFAULT_BITMAP_DISTANT_COMMIT_SPAN}
     *
     * @return the span of commits when building bitmaps for distant history
     * @since 4.2
     */
    public int getBitmapDistantCommitSpan() {
        return bitmapDistantCommitSpan;
    }

    /**
     * Set the span of commits when building bitmaps for distant history.
     *
     * Default setting: {@value #DEFAULT_BITMAP_DISTANT_COMMIT_SPAN}
     *
     * @param span
     *            the span of commits when building bitmaps for distant history
     * @since 4.2
     */
    public void setBitmapDistantCommitSpan(int span) {
        bitmapDistantCommitSpan = span;
    }

    /**
     * Get the count of branches deemed "excessive". If the count of branches in
     * a repository exceeds this number and bitmaps are enabled, "inactive"
     * branches will have fewer bitmaps than "active" branches.
     *
     * Default setting: {@value #DEFAULT_BITMAP_EXCESSIVE_BRANCH_COUNT}
     *
     * @return the count of branches deemed "excessive"
     * @since 4.2
     */
    public int getBitmapExcessiveBranchCount() {
        return bitmapExcessiveBranchCount;
    }

    /**
     * Set the count of branches deemed "excessive". If the count of branches in
     * a repository exceeds this number and bitmaps are enabled, "inactive"
     * branches will have fewer bitmaps than "active" branches.
     *
     * Default setting: {@value #DEFAULT_BITMAP_EXCESSIVE_BRANCH_COUNT}
     *
     * @param count
     *            the count of branches deemed "excessive"
     * @since 4.2
     */
    public void setBitmapExcessiveBranchCount(int count) {
        bitmapExcessiveBranchCount = count;
    }

    /**
     * Get the age in days that marks a branch as "inactive".
     *
     * Default setting: {@value #DEFAULT_BITMAP_INACTIVE_BRANCH_AGE_IN_DAYS}
     *
     * @return the age in days that marks a branch as "inactive"
     * @since 4.2
     */
    public int getBitmapInactiveBranchAgeInDays() {
        return bitmapInactiveBranchAgeInDays;
    }

    /**
     * Get the max time to spend during the search for reuse phase.
     *
     * Default setting: {@value #DEFAULT_SEARCH_FOR_REUSE_TIMEOUT}
     *
     * @return the maximum time to spend during the search for reuse phase.
     * @since 5.13
     */
    public Duration getSearchForReuseTimeout() {
        return searchForReuseTimeout;
    }

    /**
     * Set the age in days that marks a branch as "inactive".
     *
     * Default setting: {@value #DEFAULT_BITMAP_INACTIVE_BRANCH_AGE_IN_DAYS}
     *
     * @param ageInDays
     *            the age in days that marks a branch as "inactive"
     * @since 4.2
     */
    public void setBitmapInactiveBranchAgeInDays(int ageInDays) {
        bitmapInactiveBranchAgeInDays = ageInDays;
    }

    /**
     * Set the max time to spend during the search for reuse phase.
     *
     * @param timeout
     *            max time allowed during the search for reuse phase
     *
     *            Default setting: {@value #DEFAULT_SEARCH_FOR_REUSE_TIMEOUT}
     * @since 5.13
     */
    public void setSearchForReuseTimeout(Duration timeout) {
        searchForReuseTimeout = timeout;
    }

    /**
     * Update properties by setting fields from the configuration.
     *
     * If a property's corresponding variable is not defined in the supplied
     * configuration, then it is left unmodified.
     *
     * @param rc
     *            configuration to read properties from.
     */
    public void fromConfig(Config rc) {
        setMaxDeltaDepth(rc.getInt(CONFIG_PACK_SECTION, CONFIG_KEY_DEPTH,
                getMaxDeltaDepth()));
        setDeltaSearchWindowSize(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_WINDOW, getDeltaSearchWindowSize()));
        setDeltaSearchMemoryLimit(rc.getLong(CONFIG_PACK_SECTION,
                CONFIG_KEY_WINDOW_MEMORY, getDeltaSearchMemoryLimit()));
        setDeltaCacheSize(rc.getLong(CONFIG_PACK_SECTION,
                CONFIG_KEY_DELTA_CACHE_SIZE, getDeltaCacheSize()));
        setDeltaCacheLimit(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_DELTA_CACHE_LIMIT, getDeltaCacheLimit()));
        setCompressionLevel(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_COMPRESSION, rc.getInt(CONFIG_CORE_SECTION,
                        CONFIG_KEY_COMPRESSION, getCompressionLevel())));
        setIndexVersion(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_INDEXVERSION,
                getIndexVersion()));
        setBigFileThreshold(rc.getInt(CONFIG_CORE_SECTION,
                CONFIG_KEY_BIGFILE_THRESHOLD, getBigFileThreshold()));
        setThreads(rc.getInt(CONFIG_PACK_SECTION, CONFIG_KEY_THREADS,
                getThreads()));

        // These variables aren't standardized
        setReuseDeltas(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_REUSE_DELTAS, isReuseDeltas()));
        setReuseObjects(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_REUSE_OBJECTS, isReuseObjects()));
        setDeltaCompress(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_DELTA_COMPRESSION, isDeltaCompress()));
        setCutDeltaChains(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_CUT_DELTACHAINS, getCutDeltaChains()));
        setSinglePack(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_SINGLE_PACK,
                getSinglePack()));
        setBuildBitmaps(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_BUILD_BITMAPS, isBuildBitmaps()));
        setBitmapContiguousCommitCount(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_BITMAP_CONTIGUOUS_COMMIT_COUNT,
                getBitmapContiguousCommitCount()));
        setBitmapRecentCommitCount(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_BITMAP_RECENT_COMMIT_COUNT,
                getBitmapRecentCommitCount()));
        setBitmapRecentCommitSpan(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_BITMAP_RECENT_COMMIT_COUNT,
                getBitmapRecentCommitSpan()));
        setBitmapDistantCommitSpan(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_BITMAP_DISTANT_COMMIT_SPAN,
                getBitmapDistantCommitSpan()));
        setBitmapExcessiveBranchCount(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_BITMAP_EXCESSIVE_BRANCH_COUNT,
                getBitmapExcessiveBranchCount()));
        setBitmapInactiveBranchAgeInDays(rc.getInt(CONFIG_PACK_SECTION,
                CONFIG_KEY_BITMAP_INACTIVE_BRANCH_AGE_INDAYS,
                getBitmapInactiveBranchAgeInDays()));
        setSearchForReuseTimeout(Duration.ofSeconds(rc.getTimeUnit(
                CONFIG_PACK_SECTION, null,
                CONFIG_KEY_SEARCH_FOR_REUSE_TIMEOUT,
                getSearchForReuseTimeout().getSeconds(), TimeUnit.SECONDS)));
        setWaitPreventRacyPack(rc.getBoolean(CONFIG_PACK_SECTION,
                CONFIG_KEY_WAIT_PREVENT_RACYPACK, isWaitPreventRacyPack()));
        setMinSizePreventRacyPack(rc.getLong(CONFIG_PACK_SECTION,
                CONFIG_KEY_MIN_SIZE_PREVENT_RACYPACK,
                getMinSizePreventRacyPack()));
    }

    /** {@inheritDoc} */
    @Override
    public String toString() {
        final StringBuilder b = new StringBuilder();
        b.append("maxDeltaDepth=").append(getMaxDeltaDepth()); //$NON-NLS-1$
        b.append(", deltaSearchWindowSize=").append(getDeltaSearchWindowSize()); //$NON-NLS-1$
        b.append(", deltaSearchMemoryLimit=") //$NON-NLS-1$
                .append(getDeltaSearchMemoryLimit());
        b.append(", deltaCacheSize=").append(getDeltaCacheSize()); //$NON-NLS-1$
        b.append(", deltaCacheLimit=").append(getDeltaCacheLimit()); //$NON-NLS-1$
        b.append(", compressionLevel=").append(getCompressionLevel()); //$NON-NLS-1$
        b.append(", indexVersion=").append(getIndexVersion()); //$NON-NLS-1$
        b.append(", bigFileThreshold=").append(getBigFileThreshold()); //$NON-NLS-1$
        b.append(", threads=").append(getThreads()); //$NON-NLS-1$
        b.append(", reuseDeltas=").append(isReuseDeltas()); //$NON-NLS-1$
        b.append(", reuseObjects=").append(isReuseObjects()); //$NON-NLS-1$
        b.append(", deltaCompress=").append(isDeltaCompress()); //$NON-NLS-1$
        b.append(", buildBitmaps=").append(isBuildBitmaps()); //$NON-NLS-1$
        b.append(", bitmapContiguousCommitCount=") //$NON-NLS-1$
                .append(getBitmapContiguousCommitCount());
        b.append(", bitmapRecentCommitCount=") //$NON-NLS-1$
                .append(getBitmapRecentCommitCount());
        b.append(", bitmapRecentCommitSpan=") //$NON-NLS-1$
                .append(getBitmapRecentCommitSpan());
        b.append(", bitmapDistantCommitSpan=") //$NON-NLS-1$
                .append(getBitmapDistantCommitSpan());
        b.append(", bitmapExcessiveBranchCount=") //$NON-NLS-1$
                .append(getBitmapExcessiveBranchCount());
        b.append(", bitmapInactiveBranchAge=") //$NON-NLS-1$
                .append(getBitmapInactiveBranchAgeInDays());
        b.append(", searchForReuseTimeout") //$NON-NLS-1$
                .append(getSearchForReuseTimeout());
        b.append(", singlePack=").append(getSinglePack()); //$NON-NLS-1$
        return b.toString();
    }
}