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refs/reftable: allow disabling writing the object index

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Besides the expected "ref" and "log" records, the reftable library also
writes "obj" records. These are basically a reverse mapping of object
IDs to their respective ref records so that it becomes efficient to
figure out which references point to a specific object. The motivation
for this data structure is the "uploadpack.allowTipSHA1InWant" config,
which allows a client to fetch any object by its hash that has a ref
pointing to it.

This reverse index is not used by Git at all though, and the expectation
is that most hosters nowadays use "uploadpack.allowAnySHA1InWant". It
may thus be preferable for many users to disable writing these optional
object indices altogether to safe some precious disk space.

Add a new config "reftable.indexObjects" that allows the user to disable
the object index altogether.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt 2024-05-13 10:18:33 +02:00 committed by Junio C Hamano
parent 90db611c2a
commit afbdbfae0b
3 changed files with 77 additions and 0 deletions
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6
Documentation/config/reftable.txt
View File

@ -30,3 +30,9 @@ 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.
reftable.indexObjects::
Whether the reftable backend shall write object blocks. Object blocks
are a reverse mapping of object ID to the references pointing to them.
+
The default value is `true`.

2
refs/reftable-backend.c
View File

@ -245,6 +245,8 @@ static int reftable_be_config(const char *var, const char *value,
if (restart_interval > UINT16_MAX)
die("reftable block size cannot exceed %u", (unsigned)UINT16_MAX);
opts->restart_interval = restart_interval;
} else if (!strcmp(var, "reftable.indexobjects")) {
opts->skip_index_objects = !git_config_bool(var, value);
}
return 0;

69
t/t0613-reftable-write-options.sh
View File

@ -214,4 +214,73 @@ test_expect_success 'restart interval exceeding maximum supported interval' '
)
'
test_expect_success 'object index gets written by default with ref index' '
test_config_global core.logAllRefUpdates false &&
test_when_finished "rm -rf repo" &&
git init repo &&
(
cd repo &&
test_commit initial &&
for i in $(test_seq 5)
do
printf "update refs/heads/branch-%d HEAD\n" "$i" ||
return 1
done >input &&
git update-ref --stdin <input &&
git -c reftable.blockSize=100 pack-refs &&
cat >expect <<-EOF &&
header:
block_size: 100
ref:
- length: 53
restarts: 1
- length: 95
restarts: 1
- length: 71
restarts: 1
- length: 80
restarts: 1
obj:
- length: 11
restarts: 1
EOF
test-tool dump-reftable -b .git/reftable/*.ref >actual &&
test_cmp expect actual
)
'
test_expect_success 'object index can be disabled' '
test_config_global core.logAllRefUpdates false &&
test_when_finished "rm -rf repo" &&
git init repo &&
(
cd repo &&
test_commit initial &&
for i in $(test_seq 5)
do
printf "update refs/heads/branch-%d HEAD\n" "$i" ||
return 1
done >input &&
git update-ref --stdin <input &&
git -c reftable.blockSize=100 -c reftable.indexObjects=false pack-refs &&
cat >expect <<-EOF &&
header:
block_size: 100
ref:
- length: 53
restarts: 1
- length: 95
restarts: 1
- length: 71
restarts: 1
- length: 80
restarts: 1
EOF
test-tool dump-reftable -b .git/reftable/*.ref >actual &&
test_cmp expect actual
)
'
test_done