reftable/stack: use geometric table compaction

Hello again,

This is the sixth version my patch series that refactors the reftable compaction strategy to instead follow a geometric sequence. Changes compared to v5:

* Reworded commit message to more clearly explain that the already existing configuration to disable auto-compaction is being exposed to callers of the library.
* Simplified expression to set the disable_auto_compact configuration.

Thanks for taking a look!

-Justin

Justin Tobler (3):
reftable/stack: expose option to disable auto-compaction reftable/stack: add env to disable autocompaction reftable/stack: use geometric table compaction

 refs/reftable-backend.c    |   3 +
 reftable/reftable-writer.h |   3 +
 reftable/stack.c           | 125 +++++++++++++++++++------------------
 reftable/stack.h           |   4 --
 reftable/stack_test.c      |  77 ++++++-----------------
 t/t0610-reftable-basics.sh |  71 ++++++++++++++++-----
 6 files changed, 145 insertions(+), 138 deletions(-)

base-commit: 4b32163adf4863c6df3bb6b43540fa2ca3494e28
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1683%2Fjltobler%2Fjt%2Freftable-geometric-compaction-v6
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1683/jltobler/jt/reftable-geometric-compaction-v6
Pull-Request: https://github.com/gitgitgadget/git/pull/1683

Range-diff vs v5:

1: a7011dbc6aa ! 1: 9c8f6b336ec reftable/stack: allow disabling of auto-compaction
@@ Metadata
Author: Justin Tobler <[email protected]>

## Commit message ##
- reftable/stack: allow disabling of auto-compaction
+ reftable/stack: expose option to disable auto-compaction
+
+ The reftable stack already has a variable to configure whether or not to
+ run auto-compaction, but it is inaccessible to users of the library.
+ There exist use cases where a caller may want to have more control over
+ auto-compaction.

Move the disable_auto_compact option into reftable_write_options to
- allow a stack to be configured with auto-compaction disabled. In a
- subsequent commit, this is used to disable auto-compaction when a
- specific environment variable is set.
+ allow external callers to disable auto-compaction. This will be used in
+ a subsequent commit.

2: 7c4fe0e9ec5 ! 2: c7bc7346540 reftable/stack: add env to disable autocompaction

     @@ refs/reftable-backend.c
       
       /*
      @@ refs/reftable-backend.c: static struct ref_store *reftable_be_init(struct repository *repo,
     + 	refs->write_options.block_size = 4096;
       	refs->write_options.hash_id = repo->hash_algo->format_id;
       	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
     ++	refs->write_options.disable_auto_compact =
     ++		!git_env_bool("GIT_TEST_REFTABLE_AUTOCOMPACTION", 1);
       
     -+	if (!git_env_bool("GIT_TEST_REFTABLE_AUTOCOMPACTION", 1))
     -+		refs->write_options.disable_auto_compact = 1;
     -+
       	/*
       	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
     - 	 * This stack contains both the shared and the main worktree refs.
      
       ## t/t0610-reftable-basics.sh ##
      @@ t/t0610-reftable-basics.sh: test_expect_success 'ref transaction: writes cause auto-compaction' '

3: 8f124acf0f8 = 3: d75494a88b0 reftable/stack: use geometric table compaction

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