Subject: [PATCH 0/3] Convert index writes to use hashfile API

From: "Derrick Stolee via GitGitGadget" <[email-masked]>
Date: Fri, 26 Mar 2021 19:12:04 +0000

As I prepare some ideas on index v5, one thing that strikes me as an
interesting direction to try is to use the chunk-format API. This would make
our extension model extremely simple (they become optional chunks, easily
identified by the table of contents).

But there is a huge hurdle to even starting that investigation: the index
uses its own hashing methods, separate from the hashfile API in csum-file.c!

The internals of the algorithms are mostly identical. The only possible
change is that the buffer sizes are different: 8KB for hashfile and 128KB in
read-cache.c. I was unable to find a performance difference in these two
implementations, despite testing on several repo sizes.

There is a subtle point about how the EOIE extension works in that it needs
a hash of just the previous extension data. This is solved by adding a new
"nested hashfile" mechanism that computes the hash at one level and then
passes the data below to another hashfile. (The good news is that this
extension will not need to exist at all if we use the chunk-format API to
manage extensions.)

Thanks, -Stolee

Derrick Stolee (3):
  csum-file: add nested_hashfile()
  read-cache: use hashfile instead of git_hash_ctx
  read-cache: delete unused hashing methods

 csum-file.c  |  22 +++++++
 csum-file.h  |   9 +++
 read-cache.c | 182 ++++++++++++++++-----------------------------------
 3 files changed, 89 insertions(+), 124 deletions(-)

base-commit: 142430338477d9d1bb25be66267225fb58498d92
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-916%2Fderrickstolee%2Findex-hashfile-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-916/derrickstolee/index-hashfile-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/916
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