On 4/12/2018 5:12 AM, Junio C Hamano wrote:
Derrick Stolee <dstolee@xxxxxxxxxxxxx> writes:
+Here is a diagram to visualize the shape of the full commit graph, and
+how different generation numbers relate:
+
+ +-----------------------------------------+
+ | GENERATION_NUMBER_INFINITY = 0xFFFFFFFF |
+ +-----------------------------------------+
+ | | ^
+ | | |
+ | +------+
+ | [gen(A) = gen(B)]
+ V
+ +-------------------------------------+
+ | 0 < commit->generation < 0x40000000 |
+ +-------------------------------------+
+ | | ^
+ | | |
+ | +------+
+ | [gen(A) > gen(B)]
+ V
+ +-------------------------------------+
+ | GENERATION_NUMBER_ZERO = 0 |
+ +-------------------------------------+
+ | ^
+ | |
+ +------+
+ [gen(A) = gen(B)]
It may be just me but all I can read out of the above is that
commit->generation may store 0xFFFFFFFF, a value between 0 and
0x40000000, or 0. I cannot quite tell what the notation [gen(A)
<cmp> gen(B)] is trying to say. I am guessing "Two generation
numbers within the 'valid' range can be compared" is what the second
one is trying to say, but it is much less interesting to know that
two infinities compare equal than how generation numbers from
different classes compare, which cannot be depicted in the above
notation, I am afraid. For example, don't we want to say that a
commit with INF can never be reached by a commit with a valid
generation number, or something like that?
My intention with the arrows was to demonstrate where parent
relationships can go, and the generation-number relation between a
commit A with parent B. Clearly, this diagram is less than helpful.
Design Details
--------------
@@ -98,17 +141,12 @@ Future Work
- The 'commit-graph' subcommand does not have a "verify" mode that is
necessary for integration with fsck.
-- The file format includes room for precomputed generation numbers. These
- are not currently computed, so all generation numbers will be marked as
- 0 (or "uncomputed"). A later patch will include this calculation.
-
- After computing and storing generation numbers, we must make graph
walks aware of generation numbers to gain the performance benefits they
enable. This will mostly be accomplished by swapping a commit-date-ordered
priority queue with one ordered by generation number. The following
- operations are important candidates:
+ operation is an important candidate:
Good.
