Bitmaps provide a huge performance boost for counting objects and they
play nice with the cgit implementation.
Change-Id: I33b05a6c8f1ee2df7770f0b9fdc50d0b4bbf1029
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
A pack bitmap index is an additional index of compressed
bitmaps of the object graph. Furthermore, a logical API of the index
functionality is included, as it is expected to be used by the
PackWriter.
Compressed bitmaps are created using the javaewah library, which is a
word-aligned compressed variant of the Java bitset class based on
run-length encoding. The library only works with positive integer
values. Thus, the maximum number of ObjectIds in a pack file that
this index can currently support is limited to Integer.MAX_VALUE.
Every ObjectId is given an integer mapping. The integer is the
position of the ObjectId in the complete ObjectId list, sorted
by offset, for the pack file. That integer is what the bitmaps
use to reference the ObjectId. Currently, the new index format can
only be used with pack files that contain a complete closure of the
object graph e.g. the result of a garbage collection.
The index file includes four bitmaps for the Git object types i.e.
commits, trees, blobs, and tags. In addition, a collection of
bitmaps keyed by an ObjectId is also included. The bitmap for each entry
in the collection represents the full closure of ObjectIds reachable
from the keyed ObjectId (including the keyed ObjectId itself). The
bitmaps are further compressed by XORing the current bitmaps against
prior bitmaps in the index, and selecting the smallest representation.
The XOR'd bitmap and offset from the current entry to the position
of the bitmap to XOR against is the actual representation of the entry
in the index file. Each entry contains one byte, which is currently
used to note whether the bitmap should be blindly reused.
Change-Id: Id328724bf6b4c8366a088233098c18643edcf40f
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
CloneCommand has been creating fetch refspecs like this on bare clones:
[remote "origin"]
url = ssh://example.com/my-repo.git
fetch = +refs/heads/*:refs/heads//*
As you can see, the destination ref pattern has a superfluous slash.
It looks like this behaviour has always been the case for CloneCommand,
at least since cc2197ed when code catering to bare-clone fetch refspecs
was added. That was released with JGit v1.0 almost 2 years ago, so
there will probably be some bare repos in the wild which will have been
cloned with JGit and have these corrupted refspecs.
The effect of the corrupted fetch refspec is quite interesting. Up to
and including JGit 2.0, the corrupt refspec was tolerated and fetches
would work as intended with no indication to the user that anything was
amiss. With JGit 2.1, a change was introduced which made JGit less
tolerant, and fetches now attempt to update the non-existing ref
"refs/heads//master". No exception is raised, but the real ref -
"refs/heads/master" - is not updated.
This behaviour was noticed by a user of Agit (which does bare clones by
default and recently updated from JGit v2.0 to v2.2), reported here:
https://github.com/rtyley/agit/issues/92
If you run C-Git fetch on a bare-repo cloned by JGit, it flat-out
rejects the refspec (checked against v1.7.10.4):
fatal: Invalid refspec '+refs/heads/*:refs/heads//*'
Incidentally, C-Git does not create an explicit fetch refspec at all
when performing a bare clone - the full remote config generated by C-Git
looks like this:
[remote "origin"]
url = ssh://example.com/my-repo.git
Using JGit on such a repository works fine, so omitting the fetch
refspec entirely is also an option.
Change-Id: I14b0d359dc69b8908f68e02cea7a756ac34bf881
No longer invoke the expensive RefDatabase.isNameConflicting() check on
updating existing refs, reducing batch ref update time by ~97%.
The RefDirectory implementation of isNameConflicting() is quite
slow (it has to do an expensive loose-ref scan) but it's only necessary
to perform this check on ref update if the ref is being *created* - if
the ref already exists, we can already guarantee that it does not
conflict with any other refs.
C-Git seems to use a similar condition before making the
is_refname_available() check:
https://github.com/git/git/blob/v1.8.1.4/refs.c#L1660-L1670
As an example of the effects on performance, here's a simple timing
experiment using The BFG to remove one file from the JGit repo:
---
$ wget http://repo1.maven.org/maven2/com/madgag/bfg-repo-cleaner/1.0.1/bfg-1.0.1.jar
$ git clone --mirror https://git.eclipse.org/r/p/jgit/jgit.git
$ java -jar bfg-1.0.1.jar -D make_jgit.sh jgit.git
....
Updating references: 100% (5760/5760)
...Ref update completed in 148,949 ms.
BFG run is complete!
---
The execution time for the run is completely dominated by the batch ref
update at the end. Repeating the experiment with BFG v1.0.2 (using JGit
patched with this change), the refs update is dramatically reduced:
---
Updating references: 100% (5760/5760)
...Ref update completed in 4,327 ms.
---
Change-Id: I9057bc4ee22f9cc269b1cc00c493841c71527cd6
Previously a PackFile class was assumed to only support a .pack and .idx
file. Update the constructor to enumerate the supported extensions for
the pack file. This will allow the bitmap code to only be executed if
the bitmap extension file is known to exist.
Change-Id: Ie59041dffec5f60d7ea2771026ffd945106bd4bf
When a lot of commits are added to DateRevQueue, the
sort-on-insertion approach is very heavy on CPU cycles.
One approach to fix this was made by Dave Borowitz:
https://git.eclipse.org/r/#/c/5491/
But using Java's PriorityQueue seems to have brought some
extra overhead, and the desired performance could not be
reached.
This fix takes another approach to the insertion problem,
without changing the expected behaviour or bringing extra
memory overhead:
If we detect over 1000 commits in the DateRevQueue, a
"seek-index" is rebuilt every 1000th added commit.
The index keeps track of every 100th commit in the
DateRevQueue. During insertions, it will be used for a
preliminary scanning (binary search) of the queue, with
the intention of helping add() find a good starting point
to start walking from. After finding this starting point,
add() will step commit-by-commit until the correct
insertion place in the queue is found (today, the queue
is expected to be sorted at all times).
When applied to repositories with many refs, this approach
has proven to bring huge performance gains and scales quite
well.
For instance, in a repository with close to 80000 refs,
we could cut down the time a typical Gerrit replication
of 1 commit would take (just a push from JGit's point of
view) from 32sec down to 3.5sec.
Below you see some typical times to add a specific amount
of commits (with random commit times) to the DateRevQueue
and the difference the preliminary seek-index makes:
Commits | Index | No Index
1024 8ms 8ms
2048 13ms 9ms
4096 5ms 59ms
8192 11ms 595ms
16384 22ms 3058ms
32768 64ms 13811ms
65536 201ms 62677ms
131072 783ms 331585ms
Only one extra reference is needed for every 100 inserted
commits (and only when we see more than 1000 commits in
the queue), so the memory overhead should be negligible.
Various index-stepping values were tested, and 100 seemed to
scale very well and be effective from start.
In the future, it should probably be dynamic and based on
the number of refs in the queue, but this should serve well
as a starting point.
Note: While other fundamentally different data structures may
be more suitable, the DateRevQueue is extremely central to
many of the Git core operations. This approach was chosen,
since the effect of the patch is easy to predict in conjuction
with the current implementation. A totally new data structure
will make it harder to predict behaviour in many common and
uncommon cases (in terms of breaking ties, memory usage, cost
when using few elements, object creation/disposing overhead,
etc).
Change-Id: Ie7b99f40eacf6324bfb4716d82073adeda64d10f
Extend ResolveMerger with RecursiveMerger to merge two tips
that have up to 200 bases.
Bug: 380314
CQ: 6854
Change-Id: I6292bb7bda55c0242a448a94956f2d6a94fddbaa
Also-by: Christian Halstrick <christian.halstrick@sap.com>
Signed-off-by: Chris Aniszczyk <zx@twitter.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
* stable-2.3:
Prepare 2.3.2-SNAPSHOT builds
JGit v2.3.1.201302201838-r
Accept Change-Id even if footer contains not well-formed entries
Fix false positives in hashing used by PathFilterGroup
Change-Id: I5882aa3b482d6bcd40a45bed51e5ab03f018a5bc
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Instead of only looking for a Change-Id in the last section if it
consists only of well-formed "key: value" lines replace the last
occurrence of a valid Change-Id line in the last section. Some tools
require footer lines e.g. without a colon.
Gerrit doesn't accept Change-Id lines in the footer if the Change-Id
line doesn't start at the beginning of the line.
Bug: 400818
Change-Id: Icce54872adc8c566994beea848448a2f7ca87085
Signed-off-by: Stefan Lay <stefan.lay@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
The ByteArraySet failed to check the length of the entry correctly leading
to matches where no match should be.
Bug: 401249
Change-Id: I925bc48d9cafcdf13e1a797bb09fc2555eb270c5
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>
These imports are unused since commit
cb349da017
Change-Id: I74ea2a17bf4976d9c74255500e5deeff18208e87
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
* stable-2.3:
Prepare post 2.3.0.201302130906 builds
JGit v2.3.0.201302130906
Replace explicit version by property where possible
Add better documentation to DirCacheCheckout
Prepare post 2.3rc1 builds
JGit v2.3.0.201302060400-rc1
Change-Id: I5a7626014dc38e7623937a4241dbf8a6db05c1f9
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
This variable has been populated and never used ever since it was
introduced in v0.4.9~336 (Add "jgit clone", 2008-12-23). Remove it
to make the function easier to understand.
Change-Id: Idb7eb80bc236a20f7385ad2d6141b4d1c5c3f1cc
There is a huge performance issue when using both JGit (EGit) and Git
because JGit does not fill all dircache stat fields with the values Git
would expect. As a result thereof Git would typically revalidate a large
number of tracked files. This can take several minutes for large
repositories with many large files.
Since 1.8.2 Git will restrict stat checking to the size and whole second
part of the modification time stamp, if core.statinfo is set to
"minimal".
As JGit checks only size and modification time this is close to what
JGit already does. To make the match perfect ignore the sub-second part
of the modification time stamp if core.statinfo = minimal.
Change-Id: I8eaff1858a891571075a86db043f9d80da3d7503
Shawn Pearce
Colby Ranger
Shawn Pearce
Roberto Tyley
Gustaf Lundh
Matthias Sohn
George C. Young
Robin Rosenberg
Stefan Lay
Robin Stocker
Jonathan Nieder
Dave Borowitz
Christian Halstrick