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@xxxxxx>
---
Documentation/config.txt | 2 +
Documentation/config/reftable.txt | 14 ++++++
refs/reftable-backend.c | 32 +++++++++++++-
t/t0613-reftable-write-options.sh | 72 +++++++++++++++++++++++++++++++
4 files changed, 119 insertions(+), 1 deletion(-)
create mode 100644 Documentation/config/reftable.txt
diff --git a/Documentation/config.txt b/Documentation/config.txt
index 70b448b132..fa1469e5e7 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -497,6 +497,8 @@ 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 1cda48c504..c2c47a3bc1 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"
@@ -230,6 +231,23 @@ 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;
+ }
+
+ return 0;
+}
+
static struct ref_store *reftable_be_init(struct repository *repo,
const char *gitdir,
unsigned int store_flags)
@@ -245,12 +263,24 @@ 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
--
2.45.0
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