mirrors/jgit - jgit - source @ dussan.org

Colby Ranger 3b325917a5 Added read/write support for pack bitmap index. 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	11 years ago
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jgit	Added read/write support for pack bitmap index.	11 years ago

Colby Ranger 3b325917a5 Added read/write support for pack bitmap index.

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

11 years ago

jgit

Added read/write support for pack bitmap index.

11 years ago