The RefTree graph needs to be quickly accessed to read references.
It is also distinct graph disconnected from the rest of the
repository. Store the commit and tree objects in their own pack.
Change-Id: Icbb735be8fa91ccbf0708ca3a219b364e11a6b83
Hoist ObjectIdSet up to lib as part of the public API and add
the interface to some common types like PackIndex and JGit custom
ObjectId map types. This cleans up wrapper code in a number of
places by allowing direct use of the types as an ObjectIdSet.
Future commits can now rely on ObjectIdSet as a simple read-only
type to check a set of objects from a number of storage options.
Change-Id: Ib62b062421d475bd52abd6c84a73916ef36e084b
Introduce PostUploadHook to replace UploadPackLogger
UploadPackLogger is incorrectly named--it can be used to trigger any
post upload action, such as GC/compaction. This change introduces
PostUploadHook/PostUploadHookChain to replace
UploadPackLogger/UploadPackLoggerChain and deprecates the latter.
It also introduces PackStatistics as a replacement for
PackWriter.Statistics, since the latter is not public API.
It changes PackWriter to use PackStatistics and reimplements
PackWriter.Statistics to delegate to PackStatistics.
Change-Id: Ic51df1613e471f568ffee25ae67e118425b38986
Signed-off-by: Terry Parker <tparker@google.com>
Use AutoClosable to close resources in bundle org.eclipse.jgit
- use try-with-resource where possible
- replace use of deprecated release() by close()
Change-Id: I0f139c3535679087b7fa09649166bca514750b81
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Propagate IOException where possible when getting refs.
Currently, Repository.getAllRefs() and Repository.getTags() silently
ignores an IOException and instead returns an empty map. Repository
is a public API and as such cannot be changed until the next major
revision change. Where possible, update the internal jgit APIs to
use the RefDatabase directly, since it propagates the error.
Change-Id: I4e4537d8bd0fa772f388262684c5c4ca1929dc4c
Garbage is randomly ordered and unlikely to delta compress against
other garbage. Disable delta compression allowing objects to switch
to whole form when moving to the garbage pack.
Because the garbage is not well compressed assume deltas were not
attempted during a normal GC cycle.
Override the reuse settings, garbage that can be reused should be
reused as-is into the garbage pack rather than switching something
like the compression level during a GC. It is intended that garbage
will eventually be removed from the repository so expending CPU
time on a compression switch is not worthwhile.
Change-Id: I0e8e58ee99e5011d375d3d89c94f2957de8402b9
Instead of forcing the implementation of the DFS backend to handle
making sure the extension bits are set correctly, have the common
callers in JGit set the extension at the same time they supply the
file sizes to the pack description. This simplifies assumptions for
an implementation of the DFS backend.
Change-Id: I55142ad8ea08a3e2e8349f72b3714578eba9c342
JGit 3.0: move internal classes into an internal subpackage
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
Remove objects before optimization from DfsGarbageCollector
Just counting objects is not sufficient. There are some race
conditions with receive packs and delta base completion that
may confuse such a simple algorithm.
Instead always do the larger set computations, and rely on the
PackWriter having no objects pending as the way to avoid creating
an empty pack file.
Change-Id: Ic81fefb158ed6ef8d6522062f2be0338a49f6bc4
Simplfy caching of DfsPackDescription from PackWriter.Statistics
Let the pack description copy the relevant stats values. This
moves it out of the garbage collector and compactor algorithms,
co-locating with something that might care.
Remove some unnecessary code from the DfsPackCompactor, the stats
tracks the same information and can supply it.
Change-Id: Id64ab38d507c0ed19ae0d106862d175b7364eba3
Avoid repacking unreachable garbage in DfsGarbageCollector
If a repository has significant amounts of unreachable garbage the
final phase to coalesce it can take longer than any other part of the
garbage collection phase. Provide a setting for applications to tweak
the threshold where coalescing ends and files just remain on disk.
Change-Id: I5f11a998a7185c75ece3271d8bc6181bb83f54c1
Enable writing pack indexes with bitmaps in the GC.
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
Reduce memory held and speed up DfsGarbageCollector.
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
Update DfsGarbageCollector to not read back a pack index.
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
Rename PackConstants to PackExt, a typed pack file extension.
PackConstants previously contained string values for the pack and pack
index extension. Change PackConstant to be PackExt, a typed wrapper
around the string pack file extension.
Change-Id: I86ac4db6da8f33aa42d6f37cfcc119e819444318
Use file extension with DfsPackDescription get/set file size.
Previously the size getters and setters had explicit methods for index
and pack. Update the api to be based on the file extension. This will
make it possible to support other extensions in the future, such as
the forthcoming bitmap extensions.
Change-Id: Iab9d4abe0af65b2fc71ad71ef1db0feb6b3b5c58
Update DfsObjDatabase API to open/write by pack extension.
Previously, the DfsObjDatabase had a hardcoded getPackFile() and
getPackIndex() methods which opens a .pack and .idx file, respectively.
A future change to add a bitmap index will need to be stored in a
parallel .bitmap file. Update the DfsObjDatabase to support opening and
writing of files for any pack extension.
Change-Id: I7c403b501e242096a2d435f6865d6025a9f86108
In practice the DHT storage layer has not been performing as well as
large scale server environments want to see from a Git server.
The performance of the DHT schema degrades rapidly as small changes
are pushed into the repository due to the chunk size being less than
1/3 of the pushed pack size. Small chunks cause poor prefetch
performance during reading, and require significantly longer prefetch
lists inside of the chunk meta field to work around the small size.
The DHT code is very complex (>17,000 lines of code) and is very
sensitive to the underlying database round-trip time, as well as the
way objects were written into the pack stream that was chunked and
stored on the database. A poor pack layout (from any version of C Git
prior to Junio reworking it) can cause the DHT code to be unable to
enumerate the objects of the linux-2.6 repository in a completable
time scale.
Performing a clone from a DHT stored repository of 2 million objects
takes 2 million row lookups in the DHT to locate the OBJECT_INDEX row
for each object being cloned. This is very difficult for some DHTs to
scale, even at 5000 rows/second the lookup stage alone takes 6 minutes
(on local filesystem, this is almost too fast to bother measuring).
Some servers like Apache Cassandra just fall over and cannot complete
the 2 million lookups in rapid fire.
On a ~400 MiB repository, the DHT schema has an extra 25 MiB of
redundant data that gets downloaded to the JGit process, and that is
before you consider the cost of the OBJECT_INDEX table also being
fully loaded, which is at least 223 MiB of data for the linux kernel
repository. In the DHT schema answering a `git clone` of the ~400 MiB
linux kernel needs to load 248 MiB of "index" data from the DHT, in
addition to the ~400 MiB of pack data that gets sent to the client.
This is 193 MiB more data to be accessed than the native filesystem
format, but it needs to come over a much smaller pipe (local Ethernet
typically) than the local SATA disk drive.
I also never got around to writing the "repack" support for the DHT
schema, as it turns out to be fairly complex to safely repack data in
the repository while also trying to minimize the amount of changes
made to the database, due to very common limitations on database
mutation rates..
This new DFS storage layer fixes a lot of those issues by taking the
simple approach for storing relatively standard Git pack and index
files on an abstract filesystem. Packs are accessed by an in-process
buffer cache, similar to the WindowCache used by the local filesystem
storage layer. Unlike the local file IO, there are some assumptions
that the storage system has relatively high latency and no concept of
"file handles". Instead it looks at the file more like HTTP byte range
requests, where a read channel is a simply a thunk to trigger a read
request over the network.
The DFS code in this change is still abstract, it does not store on
any particular filesystem, but is fairly well suited to the Amazon S3
or Apache Hadoop HDFS. Storing packs directly on HDFS rather than
HBase removes a layer of abstraction, as most HBase row reads turn
into an HDFS read.
Most of the DFS code in this change was blatently copied from the
local filesystem code. Most parts should be refactored to be shared
between the two storage systems, but right now I am hesistent to do
this due to how well tuned the local filesystem code currently is.
Change-Id: Iec524abdf172e9ec5485d6c88ca6512cd8a6eafb
Shawn Pearce
Terry Parker
Matthias Sohn
Colby Ranger
Shawn Pearce