refs/reftable: allow configuring restart interval
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@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Patrick Steinhardt committed
May 13, 2024 at 10:18 UTC
90db611c2a1f4ca2123ef5a8d7e592fa348bb23b
3 files changed
+66
Documentation/config/reftable.txt
+18
@@ -12,3 +12,21 @@ readers during access.
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+
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The largest block size is `16777215` bytes (15.99 MiB). The default value is
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`4096` bytes (4kB). A value of `0` will use the default value.
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+
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+reftable.restartInterval::
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+ The interval at which to create restart points. The reftable backend
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+ determines the restart points at file creation. Every 16 may be
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+ more suitable for smaller block sizes (4k or 8k), every 64 for larger
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+ block sizes (64k).
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++
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+More frequent restart points reduces prefix compression and increases
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+space consumed by the restart table, both of which increase file size.
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++
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+Less frequent restart points makes prefix compression more effective,
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+decreasing overall file size, with increased penalties for readers
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+walking through more records after the binary search step.
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++
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+A maximum of `65535` restart points per block is supported.
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++
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+The default value is to create restart points every 16 records. A value of `0`
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+will use the default value.
refs/reftable-backend.c
+5
@@ -240,6 +240,11 @@ static int reftable_be_config(const char *var, const char *value,
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if (block_size > 16777215)
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die("reftable block size cannot exceed 16MB");
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opts->block_size = block_size;
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+ } else if (!strcmp(var, "reftable.restartinterval")) {
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+ unsigned long restart_interval = git_config_ulong(var, value, ctx->kvi);
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+ if (restart_interval > UINT16_MAX)
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+ die("reftable block size cannot exceed %u", (unsigned)UINT16_MAX);
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+ opts->restart_interval = restart_interval;
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}
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return 0;
t/t0613-reftable-write-options.sh
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@@ -171,4 +171,47 @@ test_expect_success 'block size exceeding maximum supported size' '
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)
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'
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+test_expect_success 'restart interval at every single record' '
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+ test_when_finished "rm -rf repo" &&
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+ git init repo &&
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+ (
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+ cd repo &&
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+ test_commit initial &&
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+ for i in $(test_seq 10)
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+ do
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+ printf "update refs/heads/branch-%d HEAD\n" "$i" ||
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+ return 1
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+ done >input &&
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+ git update-ref --stdin <input &&
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+ git -c reftable.restartInterval=1 pack-refs &&
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+
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+ cat >expect <<-EOF &&
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+ header:
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+ block_size: 4096
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+ ref:
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+ - length: 566
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+ restarts: 13
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+ log:
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+ - length: 1393
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+ restarts: 12
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+ EOF
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+ test-tool dump-reftable -b .git/reftable/*.ref >actual &&
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+ test_cmp expect actual
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+ )
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+'
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+
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+test_expect_success 'restart interval exceeding maximum supported interval' '
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+ test_when_finished "rm -rf repo" &&
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+ git init repo &&
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+ (
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+ cd repo &&
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+ test_commit initial &&
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+ cat >expect <<-EOF &&
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+ fatal: reftable block size cannot exceed 65535
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+ EOF
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+ test_must_fail git -c reftable.restartInterval=65536 pack-refs 2>err &&
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+ test_cmp expect err
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+ )
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+'
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+
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test_done