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

Instead of counting objects processed, count number of bytes added
into the window. This should rescale the progress meter so that 30%
complete means 30% of the total uncompressed content size has been
inflated and fed into the window.

In theory the progress meter should be more accurate about its
percentage complete/remaining fraction than with objects. When
counting objects small objects move the progress meter more rapidly
than large objects, but demand a smaller amount of work than large
objects being compressed.

Change-Id: Id2848c16a2148b5ca51e0ca1e29c5be97eefeb48

Instead of assuming all objects cost the same amount of time to
delta compress, aggregate the byte size of objects in the list
and partition threads with roughly equal total bytes.

Before splitting the list select the N largest paths and assign
each one to its own thread. This allows threads to get through the
worst cases in parallel before attempting smaller paths that are
more likely to be splittable.

By running the largest path buckets first on each thread the likely
slowest part of compression is done early, while progress is still
reporting a low percentage. This gives users a better impression of
how fast the phase will run. On very complex inputs the slow part
is more likely to happen first, making a user realize its time to
go grab lunch, or even run it overnight.

If the worst sections are earlier, memory overruns may show up
earlier, giving the user a chance to correct the configuration and
try again before wasting large amounts of time. It also makes it
less likely the delta compression phase reaches 92% in 30 minutes
and then crawls for 10 hours through the remaining 8%.

Change-Id: I7621c4349b99e40098825c4966b8411079992e5f

If reuseObjects=true but reuseDeltas=false the caller wants attempt
a delta for every object in the input list. Test for reuseDeltas
to ensure every object passes through the searchInWindow() method.

If no delta is possible for an object and it will be stored whole
(non-delta format), PackWriter may still reuse its content from any
source pack. This avoids an inflate()-deflate() cycle to recompress
the object contents.

Change-Id: I845caeded419ef4551ef1c85787dd5ffd73235d9

If a server is streaming 3GiB worth of pack data to a client there
is no reason to compute the CRC32 checksum on the objects. The
CRC32 code computed by PackWriter is used only in the new index
created by writeIndex(), which is never invoked for the native Git
network protocols.

Object reuse may still compute its own CRC32 to verify the data
being copied from an existing pack has not been corrupted. This
check is done by the ObjectReader that implements ObjectReuseAsIs
and has no relationship to the CRC32 being skipped during output.

Change-Id: I05626f2e0d6ce19119b57d8a27193922636d60a7

If the configuration wants to run 4 threads the delta search work
is initially split somewhat evenly across the 4 threads. During
execution some threads will finish early due to the work not being
split fairly, as the initial partitions were based on object count
and not cost to inflate or size of DeltaIndex.

When a thread finishes early it now tries to take 50% of the work
remaining on a sibling thread, and executes that before exiting.
This repeats as each thread completes until a thread has only 1
object remaining.

Repacking Blink, Chromium's new fork of WebKit (2.2M objects 3.9G):

  [pack]
    reuseDeltas = false
    reuseObjects = false
    depth = 50
    threads = 8
    window = 250
    windowMemory = 800m

  before: ~105% CPU after 80%
  after:  >780% CPU to 100%

Change-Id: I65e45422edd96778aba4b6e5a0fd489ea48e8ca3

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

This switch is called mostly for OBJ_TREE and OBJ_BLOB types, which
typically make up 66% of the objects in a repository. Simplify the
test for these common types by testing for the one bit they have in
common and returning early.

Object type 5 is currently undefined. In the old code it would hit
the default and return true. In the new code it will match the early
case and also return true. In either implementation 5 should never show
up as it is not a valid type known to Git.

Object type 6 OFS_DELTA is not permitted to be supplied here.
Object type 7 REF_DELTA is not permitted to be supplied here.

Change-Id: I0ede8acee928bb3e73c744450863942064864e9c

Shortens most of the code that touches the objectLists.

Change-Id: Ib14d366dd311e544e7ba50e9ce07a6f3ce0cf254

Clip the configured limit to Integer.MAX_VALUE at the top of the
loop, saving a compare branch per object considered. This can cut
2M branches out of a repacking of the Linux kernel.

Rewrite the logic so the primary path is to match the conditional;
most objects are larger than BLKSZ (16 bytes) and less than limit.
This may help branch prediction on CPUs if the CPU tries to assume
execution takes the side of the branch and not the second.

Change-Id: I5133d1651640939afe9fbcfd8cfdb59965c57d5a

This method is only invoked with true as the argument.
Remove the unnecessary parameter and branch, making
the code easier for the JIT to optimize.

Change-Id: I68a9cd82f197b7d00a524ea3354260a0828083c6

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

The bitmap code in PackWriter knows exactly when to use a pack as
a "cached pack". It enables cached pack usage only when the pack
has a bitmap and its entire closure of objects needs to be sent.
This is a much simpler code path to maintain, and JGit actually
has a way to write the necessary index.

Change-Id: I2645d482f8733fdf0c4120cc59ba9aa4d4ba6881

Update the dfs and file GC implementations to prepare and write
bitmaps on the packs that contain the full closure of the object
graph. Update the DfsPackDescription to include the index version.

Change-Id: I3f1421e9cd90fe93e7e2ef2b8179ae2f1ba819ed

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

Update the ObjectReuseAsIs API to support creating new
ObjectToPack with only the AnyObjectId and Git object type. This is
needed to support the future pack index bitmaps, which only contain
this information and do not want the overhead of creating a temporary
object for every ObjectId.

Change-Id: I906360b471412688bf429ecef74fd988f47875dc

getObjectList() returns a list of ObjectToPack. These can hold on to a
lot of memory. Furthermore, binary searching for objects in a sorted
array can be slow. Improve the speed and reduce the memory by creating a
copy of the ObjectId and inserting it into an ObjectIdOwnerMap.

Change-Id: Ib5aa5b7447e05938b47fa55812a87b9872c20ea7

Previously, the Dfs GC excluded objects from packs by passing a
previously written index to the PackWriter. Reading back a file on
Dfs is slow. Instead, allow the PackWriter to expose the objects
included in a pack and forward that to invocations of excludeObjects() .

Change-Id: I377cb4ab07f62cf790505e1eeb0b2efe81897c79

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

If an object is in a pack file already, delta compression will not
attempt to re-compress it. This assumes that the previous
packing already performed the optimal compression attempt, however,
the subclasses of StoredObjectRepresentation may use other heuristics
to determine if the stored format is optimal.

Change-Id: I403de522f4b0dd2667d54f6faed621f392c07786

PackWriter supports excluding objects from being written to the pack.
You may specify a PackIndex which lists all those objects which should
not go into the new pack. This feature was broken because not all
commits have been checked whether they should be excluded or not. For
other object types the exclude algorithm worked. This commit adds the
missing check.

Change-Id: Id0047098393641ccba784c58b8325175c22fcece
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Use Integer, Character, and Long valueOf methods when
passing parameters to MessageFormat and other places
that expect objects instead of primitives

Change-Id: I5942fbdbca6a378136c00d951ce61167f2366ca4

Change-Id: I763590a45d75f00a09097ab6f89581a3bbd3c797

Consider two objects A->B where A uses B as a delta base, and these
are in the same source pack file ordered as "A B".

If cached packs is enabled and B is also in the cached pack that
will be appended onto the end of the thin pack, and both A, B are
supposed to be in the thin pack, PackWriter must consider the fact
that A's base B is an edge object that claims to be part of the
new pack, but is actually "external" and cannot be written first.

If the object reuse system considered B candidates fist this bug
does not arise, as B will be marked as edge due to it existing in
the cached pack. When the A candidates are later examined, A sees a
valid delta base is available as an edge, and will not later try to
"write base first" during the writing phase.

However, when the reuse system considers A candidates first they
see that B will be in the outgoing pack, as it is still part of
the thin pack, and arrange for A to be written first. Later when A
switches from being in-pack to being an edge object (as it is part
of the cached pack) the pointer in B does not get its type changed
from ObjectToPack to ObjectId, so B thinks A is non-edge.

We work around this case by also checking that the delta base B
is non-edge before writing the object to the pack. Later when A
writes its object header, delta base B's ObjectToPack will have
an offset == 0, which makes isWritten() = false, and the OBJ_REF
delta format will be used for A's header. This will be resolved by
the client to the copy of B that appears in the later cached pack.

Change-Id: Ifab6bfdf3c0aa93649468f49bcf91d67f90362ca

Packs can contain up to 2^32-1 objects, which exceeds the range of a
Java int. Try harder to accept higher object counts in some cases by
using long more often when we are working with the object count value.

This is a trivial refactoring, we may have to make even more changes
to the object handling code to support more than 2^31-1 objects.

Change-Id: I8cd8146e97cd1c738ad5b48fa9e33804982167e7

Annotated tags are relatively rare and currently are scheduled in a
pack file near the commits, decreasing the time it takes to resolve
client requests reading tags as part of a history traversal.

Putting them first before the commits allows the storage system to
page in the tag area, and have it relatively hot in the LRU when
the nearby commit area gets examined too. Later looking at the
tree and blob data will pollute the cache, making it more likely
the tags are not loaded and would require file IO.

Change-Id: I425f1f63ef937b8447c396939222ea20fdda290f

This counter always was running 1 higher, because it incremented
after the queue was exhausted (and every object was processed). Move
increments to be after the queue has provided a result, to ensure
we do not show a higher in-progress count than total count.

Change-Id: I97f815a0492c0957300475af409b6c6260008463

Stored in a weak concurrent hash map, which we clean up while iterating.
Usually the weak reference behavior should not be necessary because
PackWriters should be released with release(), but we still want to
avoid leaks when dealing with broken client code.

Change-Id: I337abb952ac6524f7f920fedf04065edf84d01d2

Memory usage is dominated by three terms:
 - The maximum memory allocated to each delta window.
 - The maximum size of a single file held in memory during delta search.
 - ObjectToPack instances owned by the writer.

For the first two terms, rather than doing complex instrumentation of
the DeltaWindows, we just overestimate based on the config parameters
(though we may underestimate if the maximum size is not set).

For the ObjectToPack instances, we do some rough byte accounting of the
underlying Java object representation.

Change-Id: I23fe3cf9d260a91f1aeb6ea22d75af8ddb9b1939

Exposes essentially the same state machine to the programmer as is
exposed to the client via a ProgressMonitor, using a wrapper around
beginTask()/endTask().

Change-Id: Ic3622b4acea65d2b9b3551c668806981fa7293e3

Export the shallow pack information, and also a handy function to
sum up the total times.  Include the time writing out the index file,
if it was created.

Change-Id: I7f60ae6848455a357b25feedb23743bbf6c153cf
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

This implements the server side of shallow clones only (i.e.
git-upload-pack), not the client side.

CQ: 5517
Bug: 301627
Change-Id: Ied5f501f9c8d1fe90ab2ba44fac5fa67ed0035a4
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

This can be useful when implementing garbage collection and there
are packs that should not be copied, such as huge packs that have
a sibling ".keep" file alongside of them.

Callers driving PackWriter need to initialize the list of packs not
to include objects from by passing each index to excludeObjects().

Change-Id: Id7f34df69df97be406bcae184308e92b0e8690fd
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

During parsing these are used with contains(). If they are a List
type, the contains operation is not efficient. Some callers such
as UploadPack often pass a List here, so convert to Set when the
type isn't efficient for contains().

Change-Id: If948ae3bf1f46e756bd2d5db14795e12ba7a6207
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

This reverts commit 67b064fc9f.

The "tiny optimization" introduced by 67b0 turns out to have a big
savings on wall-clock time when the object store is very slow (e.g.
the DHT support in JGit), but comes with a much bigger penalty in
space used by the output stream.  CGit packed with 67b0 enabled is
7 MiB larger than it should be (36 MiB rather than 28/29 MiB).  The
much bigger Linux kernel repository gained over 200 MiB, though some
of this may have been caused by a smaller window setting.

Revert this patch as PackWriter should be optimizing for space used
rather than time spent, since its primary use is network transfer, and
that isn't free.

Change-Id: I7413a9ef89762208159b4a1adc5a22a4c9245611
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

A non-thin pack does not need to worry about preferred bases, the pack
will be self-contained and all required delta base objects will appear
within the pack itself. Obtaining the path buffer and length from the
ObjectWalk to build the preferred base table is "expensive", so avoid
the cost unless a thin pack is being constructed.

Change-Id: I16e30cd864f4189d4304e7957a7cd5bdb9e84528
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

If the "Finding sources" phase will complete in <1 second with no
delta compression enabled, don't bother showing the progress meter for
this phase.  Small repositories on the local filesystem tend to rip
through this phase always subsecond and the ProgressMonitor display
can actually slow the operation down.

If delta compression is enabled, there are two phases that may run
very quickly. Set the timer to 500 milliseconds instead, reducing the
risk that the user has to wait longer than 1 second before any sort of
output from the packer occurs.

Change-Id: I58110f17e2a5ffa0134f9768b94804d16bbb8399
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Take a very simple approach to avoiding delta chains during object
reuse: objects are now always selected from the oldest pack that
contains them.  This prevents cycles because a pack must not have
a cycle in the delta chain.  If both objects A and B are chosen
out of the same source pack then there cannot be an A->B->A cycle.

The oldest pack is also the most likely to have the smallest deltas.
Its the biggest pack in the system and probably came from the clone
(or last GC) of this repository, where all objects were previously
considered and packed tightly together.  If an object appears again
(for example due to a revert and a push into this repository) the
newer copy of won't be nearly as small as the older delta version
of it, even if the newer one is also itself a delta.

ObjectDirectory already enumerates objects during selection in this
newest->oldest order, so it already is supplying these assumptions
to PackWriter.  Taking advantage of this can speed up selection by
a tiny amount by avoiding some tests, but can also help to prevent
a cycle needing to be broken on the fly during writing.

The previous cycle breaking logic wasn't fully correct either.
If a different delta base was chosen, the new delta base might not
have been written into the output pack before the current object,
forcing the use of REF_DELTA when OFS_DELTA is always smaller.
This logic has now been reworked to always re-check the delta base
and ensure it gets written before the current object.

If a cycle occurs, it gets broken the same way as before, by
disabling delta reuse and finding an alternative form of the
object, which may require inflating/deflating in whole format.

Change-Id: I9953ab8be54ceb8b588e1280d6f7edd688887747
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

If the total number of objects to look for reuse on is under 4096
this is really close to a reasonable batch size for the DHT storage
system to lookup at once.  Combine all of the objects into a single
temporary list, perform reuse, and then prune the main lists if any
duplicate objects were detected from a selected CachedPack.

The intention here is to try and avoid 4 tiny sequential lookups
on the storage system when the time to wait for each of those to
finish is higher than the CPU time required to build (and later
GC) this temporary list.

Change-Id: I528daf9d2f7744dc4a6281750c2d61d8f9da9f3a
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Instead of looping over the objectsLists array, always set slot 0 to
null and explicitly work on the 4 indexes that matter.  This kills
some loops and increases the length of the code slightly, but I've
always really disliked that dummy 0 slot.

Change-Id: I5ad938501c1c61f637ffdaff0d0d88e3962d8942
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

During object enumeration for the thin pack, very few objects come
out that are duplicated with the cached pack. Typically these are
only cases where a blob or tree was cherry-picked forward, got a
copy or rename, or was reverted... all relatively infrequent events.

Speed up pruning of the thin pack object list by combining the phase
with the object representation selection. Implementers should already
be offering to reuse the object from the cached pack if it is stored
there, at which point the implementation can perform a very fast type
of containment test using the cached pack's identity rather than yet
another index lookup.  For the local disk case this is probably not a
big improvement, but it does help on the DHT implementation where the
two passes combined into one reduces latency.

Change-Id: I6a07fc75d9075bf6233e967360b6546f9e9a2b33
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Frequently enough I'm wondering how much of a pack is commits vs.
trees, and the total line doesn't really tell us this because its
a gross total from the pack. Computing the counts per object type
is simple during packing, as PackWriter already has everything in
memory broken up by object type.  Its virtually free to get these
values and track them.

Change-Id: Id5e6b1902ea909c72f103a0fbca5d8bc316f9ab3
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

This better matches with PackFile and CachedPack's methods
that return the same value.

Change-Id: Idb9b7c71d2048dd2344a62c2cde20b4e34529ab7
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

PackWriter incorrectly returned 0 from getObjectsNumber() when the
pack has not been written yet. This caused dumb transports like
amazon-s3:// and sftp:// to abort early and never write out a pack,
under the assumption that the pack had no objects.

Until the pack header is written to the output stream, compute the
current object count each time it is requested. Once the header is
started, use the object count from the stats object.

Change-Id: I041a2368ae0cfe6f649ec28658d41a6355933900
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

OwnerMap is about 200 ms faster than SubclassMap, more friendly to the
GC, and uses less storage: testing the "Counting objects" part of
PackWriter on 1886362 objects:

  ObjectIdSubclassMap:
    load factor 50%
    table: 4194304 (wasted 2307942)
    ms spent 36998 36009 34795 34703 34941 35070 34284 34511 34638 34256
    ms avg 34800 (last 9 runs)

  ObjectIdOwnerMap:
    load factor 100%
    table: 2097152 (wasted 210790)
    directory: 1024
    ms spent 36842 35112 34922 34703 34580 34782 34165 34662 34314 34140
    ms avg 34597 (last 9 runs)

The major difference with OwnerMap is entries must extend from
ObjectIdOwnerMap.Entry, where the OwnerMap has injected its own
private "next" field into each object. This allows the OwnerMap to use
a singly linked list for chaining collisions within a bucket. By
putting collisions in a linked list, we gain the entire table back for
the SHA-1 bits to index their own "private" slot.

Unfortunately this means that each object can appear in at most ONE
OwnerMap, as there is only one "next" field within the object instance
to thread into the map. For types that are very object map heavy like
RevWalk (entity RevObject) and PackWriter (entity ObjectToPack) this
is sufficient, these entity types are only put into one map by their
container.  By introducing a new map type, we don't break existing
applications that might be trying to use ObjectIdSubclassMap to track
RevCommits they obtained from a RevWalk.

The OwnerMap uses less memory. Each object uses 1 reference more (so
we're up 1,886,362 references), but the table is 1/2 the size (2^20
rather than 2^21). The table itself wastes only 210,790 slots, rather
than 2,307,942. So OwnerMap is wasting 200k fewer references.

OwnerMap is more friendly to the GC, because it hardly ever generates
garbage. As the map reaches its 100% load factor target, it doubles in
size by allocating additional segment arrays of 2048 entries. (So the
first grow allocates 1 segment, second 2 segments, third 4 segments,
etc.)  These segments are hooked into the pre-allocated directory of
1024 spaces. This permits the map to grow to 2 million objects before
the directory itself has to grow. By using segments of 2048 entries,
we are asking the GC to acquire 8,204 bytes in a 32 bit JVM. This is
easier to satisfy then 2,307,942 bytes (for the 512k table that is
just an intermediate step in the SubclassMap). By reusing the
previously allocated segments (they are re-hashed in-place) we don't
release any memory during a table grow.

When the directory grows, it does so by discarding the old one and
using one that is 4x larger (so the directory goes to 4096 entries on
its first grow). A directory of size 4096 can handle up to 8 millon
objects. The second directory grow (16384) goes to 33 million objects.
At that point we're starting to really push the limits of the JVM
heap, but at least its many small arrays. Previously SubclassMap would
need a table of 67108864 entries to handle that object count, which
needs a single contiguous allocation of 256 MiB. That's hard to come
by in a 32 bit JVM. Instead OwnerMap uses 8192 arrays of about 8 KiB
each. This is much easier to fit into a fragmented heap.

Change-Id: Ia4acf5cfbf7e9b71bc7faa0db9060f6a969c0c50
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Instead of resizing an ArrayList until all objects have been added,
append objects into a specialized List type that uses small arrays
of 1024 entries for each 1024 objects added.

For a large repository like linux-2.6, PackWriter will now allocate
1,758 smaller arrays to hold the object list, without creating any
garbage from the intermediate states due to list expansion.

1024 was chosen as the block size (and initial directory size) as this
is a reasonable balance for the PackWriter code.  Each block uses
approximately 4096 bytes in a 32 bit JVM, as does the default top
level block directory.  The top level directory doesn't expand until 1
million items have been added to the list, which for linux-2.6 won't
yet occur as the lists are per-object-type and are thus bounded to
about 1/3 of 1.8 million.

Change-Id: If9e4092eb502394c5d3d044b58cf49952772f6d6
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

If object reuse validation is enabled, the output pack is going to
probably be stored locally.  When reusing an existing cached pack
to save object enumeration costs, ensure the cached pack has not
been corrupted by checking its SHA-1 trailer.  If it has, writing
will abort and the output pack won't be complete.  This prevents
anyone from trying to use the output pack, and catches corruption
before it can be carried any further.

Change-Id: If89d0d4e429d9f4c86f14de6c0020902705153e6
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

There is no need to validate the object contents during
copyObjectAsIs if the result is going to be parsed by unpack-objects
or index-pack.  Both programs will compute the SHA-1 of the object,
and also validate most of the pack structure.  For git daemon
like servers, this work is already done on the client end of the
connection, so the server doesn't need to repeat that work itself.

Disable object validation for the 3 transport cases where we know
the remote side will handle object validation for us (push, bundle
creation, and upload pack).  This improves performance on the server
side by reducing the work that must be done.

Change-Id: Iabb78eec45898e4a17f7aab3fb94c004d8d69af6
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Annotated tags need to be parsed by many viewing tools, but putting
them at the end of the pack hurts because kernel prefetching might
not have loaded them, since they are so far from the commits they
reference.

Position tags right behind the commits, but before the trees.
Typically the annotated tag set for a repository is very small,
so the extra prefetch burden it puts on tools that don't need
annotated tags (but do need commits and trees) is fairly low.

Change-Id: Ibbabdd94e7d563901c0309c79a496ee049cdec50
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

This simple refactoring makes it easier to pre-process each of the
object lists before its handed into the actual write routine.

Change-Id: Iea95e5ecbc7374f6bcbb43d1c75285f4f564d09d
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>