Change-Id: Ife94d1f0279ed3671a9bca79fb26c0403549fa17
Signed-off-by: David Pursehouse <david.pursehouse@sonymobile.com>

The Repository class provides only one method to look up a ref by
name, getRef.  If I request refs/heads/master and that ref does not
exist, getRef will look further in the search path:

 ref/refs/heads/master
 refs/heads/refs/heads/master
 refs/remotes/refs/heads/master

This behavior is counterintuitive, needlessly inexpensive, and usually
not what the caller expects.

Allow callers to specify whether to use the search path by providing
two separate methods:

- exactRef, which looks up a ref when its exact name is known
- findRef, which looks for a ref along the search path

For backward compatibility, keep getRef as a deprecated synonym for
findRef.

This change introduces findRef and exactRef but does not update
callers outside tests to use them yet.

Change-Id: I35375d942baeb3ded15520388f8ebb9c0cc86f8c
Signed-off-by: Jonathan Nieder <jrn@google.com>

This class requires resources which are private to another
bundle. Move the class next to its resources, removing an
odd cross bundle dependency.

Change-Id: I30d5568b09ea5fb3bd3bb60b602f149c0867f49a

Change-Id: Iedb54eb9d8396bc3ae66d8754c1527fd9ca655f9

CQ: 6570
Bug: 351806
Change-Id: I5e47810376419264ecf4247b5a333af5c8945080
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

CQ: 6385
Bug: 365444
Change-Id: I2d5164cd92429673fe3c37e9f5f9bc565192cc12
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

jgit.storage.dht is a storage provider implementation for JGit that
permits storing the Git repository in a distributed hashtable, NoSQL
system, or other database.  The actual underlying storage system is
undefined, and can be plugged in by implementing 7 small interfaces:

  *  Database
  *  RepositoryIndexTable
  *  RepositoryTable
  *  RefTable
  *  ChunkTable
  *  ObjectIndexTable
  *  WriteBuffer

The storage provider interface tries to assume very little about the
underlying storage system, and requires only three key features:

  *  key -> value lookup (a hashtable is suitable)
  *  atomic updates on single rows
  *  asynchronous operations (Java's ExecutorService is easy to use)

Most NoSQL database products offer all 3 of these features in their
clients, and so does any decent network based cache system like the
open source memcache product.  Relying only on key equality for data
retrevial makes it simple for the storage engine to distribute across
multiple machines.  Traditional SQL systems could also be used with a
JDBC based spi implementation.

Before submitting this change I have implemented six storage systems
for the spi layer:

  * Apache HBase[1]
  * Apache Cassandra[2]
  * Google Bigtable[3]
  * an in-memory implementation for unit testing
  * a JDBC implementation for SQL
  * a generic cache provider that can ride on top of memcache

All six systems came in with an spi layer around 1000 lines of code to
implement the above 7 interfaces.  This is a huge reduction in size
compared to prior attempts to implement a new JGit storage layer.  As
this package shows, a complete JGit storage implementation is more
than 17,000 lines of fairly complex code.

A simple cache is provided in storage.dht.spi.cache.  Implementers can
use CacheDatabase to wrap any other type of Database and perform fast
reads against a network based cache service, such as the open source
memcached[4].  An implementation of CacheService must be provided to
glue this spi onto the network cache.

[1] https://github.com/spearce/jgit_hbase
[2] https://github.com/spearce/jgit_cassandra
[3] http://labs.google.com/papers/bigtable.html
[4] http://memcached.org/

Change-Id: I0aa4072781f5ccc019ca421c036adff2c40c4295
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>