DeltaIndex is a simple pack style delta generator. The function works
by creating a compact index of a source buffer's blocks, and then
walking a sliding window along a desired result buffer, searching for
the window in the index. When a match is found, the window is
stretched to the longest possible length that is common with the
source buffer, and a copy instruction is created.
Rabin's polynomial hash function is used to compute the hash for a
block, permitting efficient sliding of the window in single byte
increments. The update function to slide one byte originated from
David Mazieres' work in LBFS, and our implementation of the update
step was certainly inspired by the initial work Geert Bosch proposed
for C Git in http://marc.info/?l=git&m=114565424620771&w=2.
To ensure the encoder runs in linear time with respect to the size of
the two input buffers (source and result), the maximum number of
blocks that can share the same position in the index's hashtable is
capped at a constant number. This prevents bad inputs from causing
the encoder to run in quadratic time, but comes with a penalty of
creating a longer delta due to fewer considered copy positions.
Strange hackery is used to cap the amount of memory used by the index
to be no more than 12 bytes for every 16 bytes of source buffer, no
matter what the JVM per-object overhead is. This permits an index to
always be no larger than 1.75x the source buffer length, which is an
important feature to support large windows of candidates to match
against while packing. Here the strange hackery is nothing more than
a manually managed chained hashtable, where pointers are array indexes
into storage arrays rather than object references.
Computation of the hash function for a single fixed sized block is
done through an unrolled loop, where the first 4 iterations have been
manually reduced down to eliminate unnecessary instructions. The
pattern is derived from ObjectId.equals(byte[], int, byte[], int),
where we have unrolled the loop required to compare two 20 byte
arrays. Hours of testing with the Sun 1.6 JRE concluded that the
non-obvious "foo[idx + 1]" style of reference is faster than
"foo[idx++]", and so that is what we use here during hashing.
Change-Id: If9fb2a1524361bc701405920560d8ae752221768
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Its useful to know what the flags are or what the base that was
selected is. Dump these out as part of the object's toString.
Change-Id: I8810067fb8337b08b4fcafd5f9ea3e1e31ca6726
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
A subclass may want to use this method to release handles that are
caching reuse information. Make it protected so they can override
it and update themselves.
Change-Id: I2277a56ad28560d2d2d97961cbc74bc7405a70d4
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Searching for reuse candidates should be fast compared to actually
doing delta compression. So pull the progress monitor out of this
phase and rename it back to identify the compressing objects state.
Change-Id: I5eb80919f21c1251e0e3420ff7774126f1f79b27
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Long ago when PackWriter is first written we thought that the delta
depth could be updated automatically. But its never used. Instead
make this a simple standard setter so the caller can more directly
set the delta depth of this object. This permits us to configure a
depth that takes into account more than just the depth of another
object in this same pack.
Change-Id: I1d71b74f2edd7029b8743a2c13b591098ce8cc8f
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>
This flag will later control whether or not PackWriter search for a
delta base for this object. Edge objects will never get searched,
as the writer won't be outputting them, so they should always have
this flag set on. Sometime in the future this flag should also be
set for file blobs on file paths that have the "-delta" gitattribute
set in the repository's attributes file.
Change-Id: I6e518e1a6996c8ce00b523727f1b605e400e82c6
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>
C Git allows this and it is quite handy.
Change-Id: I1d0238b43fca931ad2079649fb7b431e2815c351
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
We need to remember these so we can later cluster objects that
have similar file paths near each other as we search for deltas
between them.
Change-Id: I52cb1e4ca15c9c267a2dbf51dd0d795f885f4cf8
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
PackWriter wants to categorize objects that are similar in path name,
so blobs that are probably from the same file (or same sort of file)
can be delta compressed against each other. Avoid converting into
a string by performing the hashing directly against the path buffer
in the tree iterator.
We only hash the last 16 bytes of the path, and we try avoid any
spaces, as we want the suffix of a file such as ".java" to be more
important than the directory it is in, like "src".
Change-Id: I31770ee711526306769a6f534afb19f937e0ba85
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
This is an informational function used by PackWriter to help it
better organize objects for delta compression. Storage systems
can implement it to provide up more detailed size information,
or they can simply rely on the default behavior that uses the
ObjectLoader obtained from open.
For local file storage, we can obtain this information faster
through specialized routines that parse a pack object header.
Change-Id: I13a09b4effb71ea5151b51547f7d091564531e58
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
If the heap limit was set to something smaller than 8 KiB, we were
still allocating the full 8 KiB block size, and accepting up to
the amount we allocated by. Instead actually put a hard cap on
the limit.
Change-Id: Id1da26fde2102e76510b1da4ede8493928a981cc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Added support for converting DiffEntrys to FileHeaders. FileHeaders
are DiffEntrys with a buffer containing the diff output as well as
a list of HunkHeaders. The HunkHeaders contain EditLists. The
createFileHeader(DiffEntry) method in DiffFormatter performs a Myers
Diff on the files refered to by the DiffEntry, then puts the returned
EditList into a single HunkHeader, which is then put into the
FileHeader to be returned. It also generates the appropriate diff
header an puts it into the FileHeader's buffer. The rest of the diff
output, which would normally be parsed to generate the HunkHeaders,
is not generated. In fact, the purpose of this method is to avoid
the costly diff output generation and parsing normally required to
create a FileHeader.
Change-Id: I7d8b18c0f6c85e3d02ad58995d3d231e69af5887
There were some small errors which made it
difficult to read the JavaDoc.
Change-Id: Ib3b34353465162adebaca3514d596d0edf5aea51
Signed-off-by: Stefan Lay <stefan.lay@sap.com>
The special value 127 here means how many bytes we can put into
a single insert command. Rather than use the magical value 127,
lets name it to better document the code.
Change-Id: I5a326f4380f6ac87987fa833e9477700e984a88e
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Although all modern delta decoders can process copy instructions
with a count as large as 0xffffff (~15.9 MiB), pack version 2 streams
are only supposed to use delta copy instructions up to 64 KiB.
Rewrite our copy instruction encode loop to use the lower 64 KiB
limit, even though modern decoders would support longer copies.
To improve encoding performance we now try to encode up to four full
copy commands in our buffer before we flush it to the stream, but
we don't try to implement full buffering here. We are just trying
to amortize the virtual method call to the destination stream when
we have to do a large copy.
Change-Id: I9410a16e6912faa83180a9788dc05f11e33fabae
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
We want to get rid of these APIs, because they don't perform as well
as DirCache/TreeWalk, or don't offer nearly as many features.
Bug: 319145
Change-Id: I2b28f9cddc36482e1ad42d53e86e9d6461ba3bfc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
The encode loop had the wrong condition, objects that are 128 bytes
in size need to have their length encoded as two bytes, not one.
Change-Id: I3bef85f2b774871ba6104042b341749eb8e7595c
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Rename the ByteWindow's inflate() method to setInput. We have
completely refactored the purpose of this method to be feeding part
(or all) of the window as input to the Inflater, and the actual
inflate activity happens in the caller.
Change-Id: Ie93a5bae0e9e637b5e822d56993ce6b562c6ad15
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
We need to validate the stream state after the InflaterInputStream
thinks the stream is done. Git expects a higher level of service from
the Inflater than the InflaterInputStream usually gives, we need to
ensure the embedded CRC is valid, and that there isn't trailing
garbage at the end of the file.
Change-Id: I1c9642a82dbd76b69e607dceccf8b85dc869a3c1
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
NB.decodeInt32(info, base + 4) already returns nanoseconds.
Therefore it must not be divided by 1000000.
Change-Id: Ie8f5c4a03f984d98935dccedc2b1ba4457094899
Signed-off-by: Stefan Lay <stefan.lay@sap.com>
The FollowFilter can be installed on a RevWalk to cause the path
to be updated through rename detection when the affected file is
found to be added to the project.
The filter works reasonably well, for example we can follow the
history of the fsck command in git-core:
$ jgit log --name-status --follow builtin/fsck.c | grep ^R
R100 builtin-fsck.c builtin/fsck.c
R099 fsck.c builtin-fsck.c
R099 fsck-objects.c fsck.c
R099 fsck-cache.c fsck-objects.c
Change-Id: I4017bcfd150126aa342fdd423a688493ca660a1f
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
This way we don't have to reparse for the rename limit every time
we create a new rename detector for a repository.
Change-Id: I669d031690b85ef4da5e39189be7173fb773fc56
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Similar to what we did with diff, implement whitespace ignore options
for log too. This requires us to define some means of creating any
RawText object type at will inside of DiffFormatter, so we define a
new factory interface to construct RawText instances on demand.
Unfortunately we have to copy the entire block of common options.
args4j only processes the options/arguments on the one command class
and Java doesn't support multiple inheritance.
Change-Id: Ia16cd3a11b850fffae9fbe7b721d7e43f1d0e8a5
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Instead of crashing, output a submodule link with the simple
"Subproject commit $fullid\n" syntax used by C Git.
Change-Id: Iae8646941683fb19b73fb038217d2e3bf5f77fa9
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Passing around the OutputStream and the Repository is crazy. Instead
put the stream in the constructor, since this formatter exists only to
output to the stream, and put the repository as a member variable that
can be optionally set.
Change-Id: I2bad012fee7f40dc1346700ebd19f1e048982878
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Implement rename detection in the command line diff and log commands.
Also support --name-status, -p and -U flags, as these can be quite
useful to view more detail.
All of the Git patch file formatting code is now moved over to the
DiffFormatter class. This permits us to reuse it in any context,
including inside of IDEs.
Change-Id: I687ccba34e18105a07e0a439d2181c323209d96c
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Content similarity based rename detection is performed only after
a linear time detection is performed using exact content match on
the ObjectIds. Any names which were paired up during that exact
match phase are excluded from the inexact similarity based rename,
which reduces the space that must be considered.
During rename detection two entries cannot be marked as a rename
if they are different types of files. This prevents a symlink from
being renamed to a regular file, even if their blob content appears
to be similar, or is identical.
Efficiently comparing two files is performed by building up two
hash indexes and hashing lines or short blocks from each file,
counting the number of bytes that each line or block represents.
Instead of using a standard java.util.HashMap, we use a custom
open hashing scheme similiar to what we use in ObjecIdSubclassMap.
This permits us to have a very light-weight hash, with very little
memory overhead per cell stored.
As we only need two ints per record in the map (line/block key and
number of bytes), we collapse them into a single long inside of
a long array, making very efficient use of available memory when
we create the index table. We only need object headers for the
index structure itself, and the index table, but not per-cell.
This offers a massive space savings over using java.util.HashMap.
The score calculation is done by approximating how many bytes are
the same between the two inputs (which for a delta would be how much
is copied from the base into the result). The score is derived by
dividing the approximate number of bytes in common into the length
of the larger of the two input files.
Right now the SimilarityIndex table should average about 1/2 full,
which means we waste about 50% of our memory on empty entries
after we are done indexing a file and sort the table's contents.
If memory becomes an issue we could discard the table and copy all
records over to a new array that is properly sized.
Building the index requires O(M + N log N) time, where M is the
size of the input file in bytes, and N is the number of unique
lines/blocks in the file. The N log N time constraint comes
from the sort of the index table that is necessary to perform
linear time matching against another SimilarityIndex created for
a different file.
To actually perform the rename detection, a SxD matrix is created,
placing the sources (aka deletions) along one dimension and the
destinations (aka additions) along the other. A simple O(S x D)
loop examines every cell in this matrix.
A SimilarityIndex is built along the row and reused for each
column compare along that row, avoiding the costly index rebuild
at the row level. A future improvement would be to load a smaller
square matrix into SimilarityIndexes and process everything in that
sub-matrix before discarding the column dimension and moving down
to the next sub-matrix block along that same grid of rows.
An optional ProgressMonitor is permitted to be passed in, allowing
applications to see the progress of the detector as it works through
the matrix cells. This provides some indication of current status
for very long running renames.
The default line/block hash function used by the SimilarityIndex
may not be optimal, and may produce too many collisions. It is
borrowed from RawText's hash, which is used to quickly skip out of
a longer equality test if two lines have different hash functions.
We may need to refine this hash in the future, in order to minimize
the number of collisions we get on common source files.
Based on a handful of test commits in JGit (especially my own
recent rename repository refactoring series), this rename detector
produces output that is very close to C Git. The content similarity
scores are sometimes off by 1%, which is most probably caused by
our SimilarityIndex type using a different hash function than C
Git uses when it computes the delta size between any two objects
in the rename matrix.
Bug: 318504
Change-Id: I11dff969e8a2e4cf252636d857d2113053bdd9dc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Alex pointed out that my description of a bare repository might be
confusing for some readers. Reword the description of the error,
and make it consistent throughout the Repository class's API.
Change-Id: I87929ddd3005f578a7022f363270952d1f7f8664
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
During code review, Alex raised a few comments about commit
532421d989 ("Refactor repository construction to builder class").
Due to the size of the related series we aren't going to go back
and rebase in something this minor, so resolve them as a follow-up
commit instead.
Change-Id: Ied52f7a8f7252743353c58d20bfc3ec498933e00
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Now that any large objects are forced through a streaming loader
when its bigger than getStreamFileThreshold(), and that threshold
is pegged at Integer.MAX_VALUE as its largest size, we will never
be able to reach this code path where we threw OutOfMemoryError.
Robin pointed out that we probably should include a message here,
but the code is effectively unreachable, so there isn't any value
in adding a message at this point.
So remove it.
Change-Id: Ie611d005622e38a75537f1350246df0ab89dd500
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Since we don't know the type of object we are parsing, we don't
know if its a massive blob, or some small commit or annotated tag.
Avoid pulling the cached bytes until we have checked the type and
decided if we actually need them to continue parsing right now.
This way large blobs which won't fit in memory and would throw
a LargeObjectException don't abort parsing.
Change-Id: Ifb70df5d1c59f616aa20ee88898cb69524541636
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Callers don't necessarily need the getSize() result from a large
delta. They instead should be always using openStream() or copyTo()
for blobs going to local files, or they should be checking the
result of the constant-time isLarge() method to determine the type
of access they can use on the ObjectLoader. Avoid inflating the
delta instruction stream twice by delaying the decoding of the size
until after we have created the DeltaStream and decoded the header.
Likewise with the type, callers don't necessarily always need it
to be present in an ObjectLoader. Delay looking at it as late as
we can, thereby avoiding an ugly O(N^2) loop looking up the type
for every single object in the entire delta chain.
Change-Id: I6487b75b52a5d201d811a8baed2fb4fcd6431320
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
We default this to 1 MiB for now, but we allow users to modify
it through the Repository's configuration file to be a different
value. A new repository listener is used to identify when the
setting has been updated and trigger a reconfiguration of any
active ObjectReaders.
To prevent a horrible explosion we cap core.streamFileThreshold
at no more than 1/4 of the maximum JVM heap size. We do this
because we need at least 2 byte arrays equal in size to the
stream threshold for the worst case delta inflation scenario,
and our host application probably also needs some amount of the
heap for their working set size.
Change-Id: I103b3a541dc970bbf1a6d92917a12c5a1ee34d6c
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Very large delta instruction streams, or deltas which use very large
base objects, are now streamed through as large objects rather than
being inflated into a byte array.
This isn't the most efficient way to access delta encoded content, as
we may need to rewind and reprocess the base object when there was a
block moved within the file, but it will at least prevent the JVM from
having its heap explode.
When streaming a delta we have an inflater open for each level in the
delta chain, to inflate the instruction set of the delta, as well as
an inflater for the base level object. The base object is buffered,
as is the top level delta requested by the application, but we do not
buffer the intermediate delta streams. This keeps memory usage lower,
so its closer to 1024 bytes per level in the chain, without having an
adverse impact on raw throughput as the top-level buffer gets pushed
down to the lowest stream that has the next region.
Delta instructions transparently collapse here, if the top level does
not copy a region from its base, the base won't materialize that part
from its own base, etc. This allows us to avoid copying around a lot
of segments which have been deleted from the final version.
Change-Id: I724d45245cebb4bad2deeae7b896fc55b2dd49b3
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Similar to the loose object support, whole packed objects can
now be streamed back to the caller. The streaming is less
efficient as we copy the data from the cached window array
into the InflaterInputStream's internal buffer, then inflate
it there before returning to the application.
Like with unpacked objects, there is plenty of room for some
optimization, especially for the copyTo method, where we don't
necessarily need so much buffering to exist.
Change-Id: Ie23be81289e37e24b91d17b0891e47b9da988008
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
The class is identical, but ObjectLoader.SmallObject is part of our
public API for storage implementations to build on top of.
Change-Id: I381a3953b14870b6d3d74a9c295769ace78869dc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Big loose objects can now be streamed if they are over the large
object size threshold. This prevents the JVM heap from exploding
with a very large byte array to hold the slurped file, and then
again with its uncompressed copy.
We may have slightly slowed down the simple case for small
loose objects, as the loader no longer slurps the entire thing
and decompresses in memory. To try and keep good performance
for the very common small objects that are below 8 KiB in size,
buffers are set to 8 KiB, causing the reader to slurp most of the
file anyway. However the data has to be copied at least once,
from the BufferedInputStream into the InflaterInputStream.
New unit tests are supplied to get nearly 100% code coverage on the
unpacked code paths, for both standard and pack style loose objects.
We tested a fair chunk of the code elsewhere, but these new tests
are better isolated to the specific branches in the code path.
Change-Id: I87b764ab1b84225e9b5619a2a55fd8eaa640e1fe
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
JGit does not currently do rename detection during diffs. I added
a class that, given a TreeWalk to iterate over, can output a list
of DiffEntry's for that TreeWalk, taking into account renames. This
class only detects renames by SHA1's. More complex rename detection,
along the lines of what C Git does will be added later.
Change-Id: I93606ce15da70df6660651ec322ea50718dd7c04
Assume that the argument of compareTo won't be mutated while we
are doing the compare, and support the wider AnyObjectId type so
MutableObjectId is suitable on either side of the compareTo call.
Change-Id: I2a63a496c0a7b04f0e5f27d588689c6d5e149d98
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
This way we can stream a large file through memory, rather than
loading the entire thing into a single contiguous byte array.
Change-Id: I3ada2856af2bf518f072edec242667a486fb0df1
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Instead of loading the entire object as a byte array and passing
that into the deflater, let the ObjectLoader copy the object onto
the DeflaterOutputStream. This has the nice side effect of using
some sort of stride hack in the Sun implementation that may improve
compression performance.
Change-Id: I3f3d681b06af0da93ab96c75468e00e183ff32fe
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Only allocate the Deflater if we can't reuse everything, but also
make sure we release it when we release the PackWriter's resources.
Change-Id: I16a32b94647af0778658eda87acbafc9a25b314a
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Blobs that are too large to read as a single byte array should be
accessed through an InputStream based interface instead, allowing
the application to walk through the data stream incrementally.
Define the basic interface to support streaming contents, but don't
implement it yet for the file based backend.
Change-Id: If9e4442e9ef4ed52c3e0f1af9398199a73145516
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Refactored a superclass out of FileHeader called DiffEntry that holds
the more general data from FileHeader that is useful in rename
detection (old/new Ids, modes, names, as well as changeType and
score). FileHeader is now a DiffEntry that adds Hunks, parsing
abilities, etc.
Change-Id: I8398728cd218f8c6e98f7a4a7f2f342391d865e4
It is possible that StreamCopyThread will not flush everything
from it's src to it's dst. In most cases StreamCopyThread works
like this:
in loop:
n = src.read(buf);
dst.write(buf, 0, n);
and when we want to flush, we interrupt() StreamCopyThread and it
flushes everything it wrote to dst.
The problem is that our interrupt() could interrupt reading. In this
case we will flush everything we wrote to dst, but not everything
we wrote to src.
Change-Id: Ifaf4d8be87535c7364dd59b217dfc631460018ff
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Instead of creating the DirCache from a static factory method, use
an instance method on Repository, permitting the implementation to
override the method with a completely different type of DirCache
reading and writing. This would better support a repository in the
cloud strategy, or even just an in-memory unit test environment.
Change-Id: I6399894b12d6480c4b3ac84d10775dfd1b8d13e7
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Using a custom exception type makes it easire for an application
developer to understand why an exception was thrown out of a method
we declare. To remain compatiable with existing callers, we still
extend off IllegalStateException.
Change-Id: Ideeef2399b11ca460a2dbb3cd80eb76aa0a025ba
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Shawn O. Pearce
Robin Rosenberg
Matthias Sohn
Jeff Schumacher
Stefan Lay
Dmitry Neverov