Bug: 431552
Change-Id: I469316f5645205016e1fa6b0fbd2ff3b509b14bc
Signed-off-by: Robin Stocker <robin@nibor.org>

Change-Id: I38f10d622c30f19d1154a4901477e844cb411707
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Some packs built by JGit have incredibly long delta chains due to a
long standing bug in PackWriter. Google has packs created by JGit's
DfsGarbageCollector with chains of 6000 objects long, or more.

Inflating objects at the end of this 6000 long chain is impossible
to complete within a reasonable time bound. It could take a beefy
system hours to perform even using the heavily optimized native C
implementation of Git, let alone with JGit.

Enable pack.cutDeltaChains to be set in a configuration file to
permit the PackWriter to determine the length of each delta chain
and clip the chain at arbitrary points to fit within pack.depth.

Delta chain cycles are still possible, but no attempt is made to
detect them. A trivial chain of A->B->A will iterate for the full
pack.depth configured limit (e.g. 50) and then pick an object to
store as non-delta.

When cutting chains the object list is walked in reverse to try
and take advantage of existing chain computations. The assumption
here is most deltas are near the end of the list, and their bases
are near the front of the list. Going up from the tail attempts to
reuse chainLength computations by relying on the memoized value in
the delta base.

The chainLength field in ObjectToPack is overloaded into the depth
field normally used by DeltaWindow. This is acceptable because the
chain cut happens before delta search, and the chainLength is reset
to 0 if delta search will follow.

Change-Id: Ida4fde9558f3abbbb77ade398d2af3941de9c812

Change-Id: Iaca88ec28b412e6b58e7b39a0762ba54b25f9471
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Change-Id: I7e0c74ecfd0e0615d10fb582b2897d33be23440a
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

This breaks all existing callers once. Applications are not supposed
to build against the internal storage API unless they can accept API
churn and make necessary updates as versions change.

Change-Id: I2ab1327c202ef2003565e1b0770a583970e432e9

This is helpful for writing the pack configuration into a log file.

Change-Id: I5e7f5ff7e01c9538ca12a1860844ba9b467bdf05
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Bitmaps provide a huge performance boost for counting objects and they
play nice with the cgit implementation.

Change-Id: I33b05a6c8f1ee2df7770f0b9fdc50d0b4bbf1029

Update the PackWriter to support writing out pack bitmap indexes,
a parallel ".bitmap" file to the ".pack" file.
Bitmaps are selected at commits every 1 to 5,000 commits for
each unique path from the start. The most recent 100 commits are
all bitmapped. The next 19,000 commits have a bitmaps every 100
commits. The remaining commits have a bitmap every 5,000 commits.
Commits with more than 1 parent are prefered over ones
with 1 or less. Furthermore, previously computed bitmaps are reused,
if the previous entry had the reuse flag set, which is set when the
bitmap was placed at the max allowed distance.

Bitmaps are used to speed up the counting phase when packing, for
requests that are not shallow. The PackWriterBitmapWalker uses
a RevFilter to proactively mark commits with RevFlag.SEEN, when
they appear in a bitmap. The walker produces the full closure
of reachable ObjectIds, given the collection of starting ObjectIds.

For fetch request, two ObjectWalks are executed to compute the
ObjectIds reachable from the haves and from the wants. The
ObjectIds needed to be written are determined by taking all the
resulting wants AND NOT the haves.

For clone requests, we get cached pack support for "free" since
it is possible to determine if all of the ObjectIds in a pack file
are included in the resulting list of ObjectIds to write.

On my machine, the best times for clones and fetches of the linux
kernel repository (with about 2.6M objects and 300K commits) are
tabulated below:

Operation                   Index V2               Index VE003
Clone                       37530ms (524.06 MiB)     82ms (524.06 MiB)
Fetch (1 commit back)          75ms                 107ms
Fetch (10 commits back)       456ms (269.51 KiB)    341ms (265.19 KiB)
Fetch (100 commits back)      449ms (269.91 KiB)    337ms (267.28 KiB)
Fetch (1000 commits back)    2229ms ( 14.75 MiB)    189ms ( 14.42 MiB)
Fetch (10000 commits back)   2177ms ( 16.30 MiB)    254ms ( 15.88 MiB)
Fetch (100000 commits back) 14340ms (185.83 MiB)   1655ms (189.39 MiB)

Change-Id: Icdb0cdd66ff168917fb9ef17b96093990cc6a98d

A few classes such as Constanrs are marked with @SuppressWarnings, as are
toString() methods with many liternal, but otherwise $NLS-n$ is used for
string containing text that should not be translated. A few literals may
fall into the gray zone, but mostly I've tried to only tag the obvious
ones.

Change-Id: I22e50a77e2bf9e0b842a66bdf674e8fa1692f590

Some embeddings of UploadPack (e.g. Gerrit Code Review) set their own
PackConfig from a server-wide configuration, overriding any JGit
defaults or settings that may exist at the local repository level.

Make a copy constructor form of PackConfig so this server-wide
configuration object can be copied and then merged with repository
specific configuration data.

Change-Id: I4463c95aeaf7d6536c3ab132dec9c50ee528d9e0
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Rather than duplicating this block everywhere, reuse the limited size
form of getCachedBytes to acquire the content of an object.

Change-Id: I2e26a823e6fd0964d8f8dbfaa0fc2e8834c179c1
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

For daemons we might want to disable delta compression entirely, or
in some strange case an administrator might need to turn of delta
reuse.  Expose these normally internal pack settings through the pack
configuration section.

Change-Id: I39bfefee8384c864cc04ffac724f197240c8a11a
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

This refactoring permits applications to configure global per-process
settings for all packing and easily pass it through to per-request
PackWriters, ensuring that the process configuration overrides the
repository specific settings.

For example this might help in a daemon environment where the server
wants to cap the resources used to serve a dynamic upload pack
request, even though the repository's own pack.* settings might be
configured to be more aggressive.  This allows fast but less bandwidth
efficient serving of clients, while still retaining good compression
through a cron managed `git gc`.

Change-Id: I58cc5e01b48924b1a99f79aa96c8150cdfc50846
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

If we have multiple CPUs available, packing usually goes faster
when each CPU is assigned a slice of the available search space.
The number of threads to use is guessed from the runtime if it
wasn't set by the caller, or wasn't set in the configuration.

Change-Id: If554fd8973db77632a52a0f45377dd6ec13fc220
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

PackWriter now caches small deltas, or deltas that are very tiny
compared to their source inputs, so that the writing phase goes
faster by reusing those cached deltas.

The cached data is stored compressed, which usually translates to
a bigger footprint due to deltas being very hard to compress, but
saves time during writing by avoiding the deflate step.  They are
held under SoftReferences so that the JVM GC can clear out deltas
if memory gets very tight.  We would rather continue working and
spend a bit more CPU time during writing than crash due to OOME.

To avoid OutOfMemoryErrors during the caching phase we also trap
OOME and just abort out of the caching.

Because deflateBound() always produces something larger than what
we need to actually store the deflated data, we copy it over into
a new buffer if the actual length doesn't match the buffer length.
When packing jgit.git this saves over 111 KiB in the cache, and is
thus a worthwhile hit on CPU time.

To further save memory we store the inflated size of the delta
(which we need for the object header) in the same field as the
pathHash, as the pathHash is no longer necessary by this phase
of the packing algorithm.

Change-Id: I0da0c600d845e8ec962289751f24e65b5afa56d7
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

C Git's fast-import uses this to determine the maximum file size
that it tries to delta compress, anything equal to or above this
setting is stored with as a whole object with simple deflate.

Define the configuration so we can use it later.

Change-Id: Iea46e787d019a1b6c51135cc73d7688a02e207f5
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

We now at least import other pack settings like pack.window, which
means we can later use these to control how we search for deltas.

The compression level was fixed to use pack.compression rather than
the loose object core.compression setting.

Change-Id: I72ff6d481c936153ceb6a9e485fa731faf075a9a
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Per CQ 3448 this is the initial contribution of the JGit project
to eclipse.org.  It is derived from the historical JGit repository
at commit 3a2dd9921c.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>