[PATCH v3 06/11] refs/reftable: allow configuring block size
- From
Patrick Steinhardt <ps@pks.im>
- Date
- May 13, 2024, 08:18 UTC
- Message-ID
- <70720af4d3476e30eba2a85c2691d664e02ade31.1715587849.git.ps@pks.im>
- In-Reply-To
- <cover.1715587849.git.ps@pks.im>
Add a new option `reftable.blockSize` that allows the user to control the block size used by the reftable library.
Signed-off-by: Patrick Steinhardt <ps@pks.im> --- Documentation/config.txt | 2 + Documentation/config/reftable.txt | 14 ++++++ refs/reftable-backend.c | 31 ++++++++++++- t/t0613-reftable-write-options.sh | 72 +++++++++++++++++++++++++++++++ 4 files changed, 118 insertions(+), 1 deletion(-) create mode 100644 Documentation/config/reftable.txt
diff --git a/Documentation/config.txt b/Documentation/config.txt index 6f649c997c..cbf0b99c44 100644 --- a/Documentation/config.txt +++ b/Documentation/config.txt @@ -498,6 +498,8 @@ include::config/rebase.txt[] include::config/receive.txt[] +include::config/reftable.txt[] + include::config/remote.txt[] include::config/remotes.txt[] diff --git a/Documentation/config/reftable.txt b/Documentation/config/reftable.txt new file mode 100644 index 0000000000..fa7c4be014 --- /dev/null +++ b/Documentation/config/reftable.txt @@ -0,0 +1,14 @@ +reftable.blockSize:: + The size in bytes used by the reftable backend when writing blocks. + The block size is determined by the writer, and does not have to be a + power of 2. The block size must be larger than the longest reference + name or log entry used in the repository, as references cannot span + blocks. ++ +Powers of two that are friendly to the virtual memory system or +filesystem (such as 4kB or 8kB) are recommended. Larger sizes (64kB) can +yield better compression, with a possible increased cost incurred by +readers during access. ++ +The largest block size is `16777215` bytes (15.99 MiB). The default value is +`4096` bytes (4kB). A value of `0` will use the default value. diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c index f8f930380d..8d0ae9e285 100644 --- a/refs/reftable-backend.c +++ b/refs/reftable-backend.c @@ -1,6 +1,7 @@ #include "../git-compat-util.h" #include "../abspath.h" #include "../chdir-notify.h" +#include "../config.h" #include "../environment.h" #include "../gettext.h" #include "../hash.h" @@ -228,6 +229,22 @@ static int read_ref_without_reload(struct reftable_stack *stack, return ret; } +static int reftable_be_config(const char *var, const char *value, + const struct config_context *ctx, + void *_opts) +{ + struct reftable_write_options *opts = _opts; + + if (!strcmp(var, "reftable.blocksize")) { + unsigned long block_size = git_config_ulong(var, value, ctx->kvi); + if (block_size > 16777215) + die("reftable block size cannot exceed 16MB"); + opts->block_size = block_size; + } + + return 0; +} + static struct ref_store *reftable_be_init(struct repository *repo, const char *gitdir, unsigned int store_flags) @@ -243,12 +260,24 @@ static struct ref_store *reftable_be_init(struct repository *repo, base_ref_store_init(&refs->base, repo, gitdir, &refs_be_reftable); strmap_init(&refs->worktree_stacks); refs->store_flags = store_flags; - 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); + git_config(reftable_be_config, &refs->write_options); + + /* + * It is somewhat unfortunate that we have to mirror the default block + * size of the reftable library here. But given that the write options + * wouldn't be updated by the library here, and given that we require + * the proper block size to trim reflog message so that they fit, we + * must set up a proper value here. + */ + if (!refs->write_options.block_size) + refs->write_options.block_size = 4096; + /* * Set up the main reftable stack that is hosted in GIT_COMMON_DIR. * This stack contains both the shared and the main worktree refs. diff --git a/t/t0613-reftable-write-options.sh b/t/t0613-reftable-write-options.sh index 462980c37c..8bdbc6ec70 100755 --- a/t/t0613-reftable-write-options.sh +++ b/t/t0613-reftable-write-options.sh @@ -99,4 +99,76 @@ test_expect_success 'many refs results in multiple blocks' ' ) ' +test_expect_success 'tiny block size leads to error' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit initial && + cat >expect <<-EOF && + error: unable to compact stack: entry too large + EOF + test_must_fail git -c reftable.blockSize=50 pack-refs 2>err && + test_cmp expect err + ) +' + +test_expect_success 'small block size leads to multiple ref blocks' ' + test_config_global core.logAllRefUpdates false && + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit A && + test_commit B && + git -c reftable.blockSize=100 pack-refs && + + cat >expect <<-EOF && + header: + block_size: 100 + ref: + - length: 53 + restarts: 1 + - length: 74 + restarts: 1 + - length: 38 + restarts: 1 + EOF + test-tool dump-reftable -b .git/reftable/*.ref >actual && + test_cmp expect actual + ) +' + +test_expect_success 'small block size fails with large reflog message' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit A && + perl -e "print \"a\" x 500" >logmsg && + cat >expect <<-EOF && + fatal: update_ref failed for ref ${SQ}refs/heads/logme${SQ}: reftable: transaction failure: entry too large + EOF + test_must_fail git -c reftable.blockSize=100 \ + update-ref -m "$(cat logmsg)" refs/heads/logme HEAD 2>err && + test_cmp expect err + ) +' + +test_expect_success 'block size exceeding maximum supported size' ' + test_config_global core.logAllRefUpdates false && + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit A && + test_commit B && + cat >expect <<-EOF && + fatal: reftable block size cannot exceed 16MB + EOF + test_must_fail git -c reftable.blockSize=16777216 pack-refs 2>err && + test_cmp expect err + ) +' + test_done
-- 2.45.GIT