Add a new option `reftable.restartInterval` that allows the user to
control the restart interval when writing reftable records used by the
reftable library.
Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
---
Documentation/config/reftable.txt | 19 ++++++++++++++
refs/reftable-backend.c | 6 +++++
t/t0613-reftable-write-options.sh | 43 +++++++++++++++++++++++++++++++
3 files changed, 68 insertions(+)
diff --git a/Documentation/config/reftable.txt b/Documentation/config/reftable.txt
index fa7c4be014..16b915c75e 100644
--- a/Documentation/config/reftable.txt
+++ b/Documentation/config/reftable.txt
@@ -12,3 +12,22 @@ 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.
+
+reftable.restartInterval::
+ The interval at which to create restart points. The reftable backend
+ determines the restart points at file creation. The process is
+ arbitrary, but every 16 or 64 records is recommended. Every 16 may be
+ more suitable for smaller block sizes (4k or 8k), every 64 for larger
+ block sizes (64k).
++
+More frequent restart points reduces prefix compression and increases
+space consumed by the restart table, both of which increase file size.
++
+Less frequent restart points makes prefix compression more effective,
+decreasing overall file size, with increased penalties for readers
+walking through more records after the binary search step.
++
+A maximum of `65535` restart points per block is supported.
++
+The default value is to create restart points every 16 records. A value of `0`
+will use the default value.
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index c2c47a3bc1..a786143de2 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -243,6 +243,12 @@ static int reftable_be_config(const char *var, const char *value,
die("reftable block size cannot exceed 16MB");
opts->block_size = block_size;
return 0;
+ } else if (!strcmp(var, "reftable.restartinterval")) {
+ unsigned long restart_interval = git_config_ulong(var, value, ctx->kvi);
+ if (restart_interval > UINT16_MAX)
+ die("reftable block size cannot exceed %u", (unsigned)UINT16_MAX);
+ opts->restart_interval = restart_interval;
+ return 0;
}
return 0;
diff --git a/t/t0613-reftable-write-options.sh b/t/t0613-reftable-write-options.sh
index 8bdbc6ec70..e0a5b26f58 100755
--- a/t/t0613-reftable-write-options.sh
+++ b/t/t0613-reftable-write-options.sh
@@ -171,4 +171,47 @@ test_expect_success 'block size exceeding maximum supported size' '
)
'
+test_expect_success 'restart interval at every single record' '
+ test_when_finished "rm -rf repo" &&
+ git init repo &&
+ (
+ cd repo &&
+ test_commit initial &&
+ for i in $(test_seq 10)
+ do
+ printf "update refs/heads/branch-%d HEAD\n" "$i" ||
+ return 1
+ done >input &&
+ git update-ref --stdin <input &&
+ git -c reftable.restartInterval=1 pack-refs &&
+
+ cat >expect <<-EOF &&
+ header:
+ block_size: 4096
+ ref:
+ - length: 566
+ restarts: 13
+ log:
+ - length: 1393
+ restarts: 12
+ EOF
+ test-tool dump-reftable -b .git/reftable/*.ref >actual &&
+ test_cmp expect actual
+ )
+'
+
+test_expect_success 'restart interval exceeding maximum supported interval' '
+ test_when_finished "rm -rf repo" &&
+ git init repo &&
+ (
+ cd repo &&
+ test_commit initial &&
+ cat >expect <<-EOF &&
+ fatal: reftable block size cannot exceed 65535
+ EOF
+ test_must_fail git -c reftable.restartInterval=65536 pack-refs 2>err &&
+ test_cmp expect err
+ )
+'
+
test_done
--
2.45.0
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