| Message ID | 20250219-pks-update-ref-optimization-v2-3-e696e7220b22@pks.im (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | refs: batch refname availability checks | expand |
On 25/02/19 02:23PM, Patrick Steinhardt wrote: > Most of the commands in git-update-ref(1) accept an old and/or new > object ID to update a specific reference to. These object IDs get parsed > via `repo_get_oid()`, which not only handles plain object IDs, but also > those that have a suffix like "~" or "^2". More surprisingly though, it > even knows to resolve references, despite the fact that its manpage does > not mention this fact even once. > > One consequence of this is that we also check for ambiguous references: > when parsing a full object ID where the DWIM mechanism would also cause > us to resolve it as a branch, we'd end up printing a warning. While this > check makes sense to have in general, it is arguably less useful in the > context of git-update-ref(1). This is out of two reasons: > > - The manpage is explicitly structured around object IDs. So if we see > a fully blown object ID, the intent should be quite clear in > general. Makes sense. > - The command is part of our plumbing layer and not a tool that users > would generally use in interactive workflows. As such, the warning > will likely not be visible to anybody in the first place. Ok, so in many cases already the warning is not propagated which makes its computation wasteful to begin with. > Furthermore, this check can be quite expensive when updating lots of > references via `--stdin`, because we try to read multiple references per > object ID that we parse according to the DWIM rules. This effect can be > seen both with the "files" and "reftable" backend. > > The issue is not unique to git-update-ref(1), but was also an issue in > git-cat-file(1), where it was addressed by disabling the ambiguity check > in 25fba78d36b (cat-file: disable object/refname ambiguity check for > batch mode, 2013-07-12). > > Disable the warning in git-update-ref(1), which provides a significant > speedup with both backends. The following benchmark creates 10000 new > references with a 100000 preexisting refs with the "files" backend: > > Benchmark 1: update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD~) > Time (mean ± σ): 467.3 ms ± 5.1 ms [User: 100.0 ms, System: 365.1 ms] > Range (min … max): 461.9 ms … 479.3 ms 10 runs > > Benchmark 2: update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD) > Time (mean ± σ): 394.1 ms ± 5.8 ms [User: 63.3 ms, System: 327.6 ms] > Range (min … max): 384.9 ms … 405.7 ms 10 runs > > Summary > update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD) ran > 1.19 ± 0.02 times faster than update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD~) > > And with the "reftable" backend: > > Benchmark 1: update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD~) > Time (mean ± σ): 146.9 ms ± 2.2 ms [User: 90.4 ms, System: 56.0 ms] > Range (min … max): 142.7 ms … 150.8 ms 19 runs > > Benchmark 2: update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD) > Time (mean ± σ): 63.2 ms ± 1.1 ms [User: 41.0 ms, System: 21.8 ms] > Range (min … max): 61.1 ms … 66.6 ms 41 runs > > Summary > update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD) ran > 2.32 ± 0.05 times faster than update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD~) > > Note that the absolute improvement with both backends is roughly in the > same ballpark, but the relative improvement for the "reftable" backend > is more significant because writing the new table to disk is faster in > the first place. > > Signed-off-by: Patrick Steinhardt <ps@pks.im> > --- > builtin/update-ref.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/builtin/update-ref.c b/builtin/update-ref.c > index 4d35bdc4b4b..d603f54b770 100644 > --- a/builtin/update-ref.c > +++ b/builtin/update-ref.c > @@ -179,7 +179,8 @@ static int parse_next_oid(const char **next, const char *end, > (*next)++; > *next = parse_arg(*next, &arg); > if (arg.len) { > - if (repo_get_oid(the_repository, arg.buf, oid)) > + if (repo_get_oid_with_flags(the_repository, arg.buf, oid, > + GET_OID_SKIP_AMBIGUITY_CHECK)) > goto invalid; > } else { > /* Without -z, an empty value means all zeros: */ > @@ -197,7 +198,8 @@ static int parse_next_oid(const char **next, const char *end, > *next += arg.len; > > if (arg.len) { > - if (repo_get_oid(the_repository, arg.buf, oid)) > + if (repo_get_oid_with_flags(the_repository, arg.buf, oid, > + GET_OID_SKIP_AMBIGUITY_CHECK)) > goto invalid; > } else if (flags & PARSE_SHA1_ALLOW_EMPTY) { > /* With -z, treat an empty value as all zeros: */ > @@ -772,7 +774,8 @@ int cmd_update_ref(int argc, > refname = argv[0]; > value = argv[1]; > oldval = argv[2]; > - if (repo_get_oid(the_repository, value, &oid)) > + if (repo_get_oid_with_flags(the_repository, value, &oid, > + GET_OID_SKIP_AMBIGUITY_CHECK)) > die("%s: not a valid SHA1", value); > } > > @@ -783,7 +786,8 @@ int cmd_update_ref(int argc, > * must not already exist: > */ > oidclr(&oldoid, the_repository->hash_algo); > - else if (repo_get_oid(the_repository, oldval, &oldoid)) > + else if (repo_get_oid_with_flags(the_repository, oldval, &oldoid, > + GET_OID_SKIP_AMBIGUITY_CHECK)) > die("%s: not a valid old SHA1", oldval); > } In builtin/update-ref.c all uses of repo_get_oid() have been converted to repo_get_oid_with_flags() with the GET_OID_SKIP_AMBIGUITY_CHECK flag except for one in parse_cmd_symref_update(). Is there reason to leave that one untouched? -Justin
On Wed, Feb 19, 2025 at 12:21:44PM -0600, Justin Tobler wrote: > > diff --git a/builtin/update-ref.c b/builtin/update-ref.c > > index 4d35bdc4b4b..d603f54b770 100644 > > --- a/builtin/update-ref.c > > +++ b/builtin/update-ref.c > > @@ -179,7 +179,8 @@ static int parse_next_oid(const char **next, const char *end, > > @@ -783,7 +786,8 @@ int cmd_update_ref(int argc, > > * must not already exist: > > */ > > oidclr(&oldoid, the_repository->hash_algo); > > - else if (repo_get_oid(the_repository, oldval, &oldoid)) > > + else if (repo_get_oid_with_flags(the_repository, oldval, &oldoid, > > + GET_OID_SKIP_AMBIGUITY_CHECK)) > > die("%s: not a valid old SHA1", oldval); > > } > > In builtin/update-ref.c all uses of repo_get_oid() have been converted > to repo_get_oid_with_flags() with the GET_OID_SKIP_AMBIGUITY_CHECK flag > except for one in parse_cmd_symref_update(). Is there reason to leave > that one untouched? Ah, no, this was a mere oversight. Good catch, fixed. Patrick
diff --git a/builtin/update-ref.c b/builtin/update-ref.c index 4d35bdc4b4b..d603f54b770 100644 --- a/builtin/update-ref.c +++ b/builtin/update-ref.c @@ -179,7 +179,8 @@ static int parse_next_oid(const char **next, const char *end, (*next)++; *next = parse_arg(*next, &arg); if (arg.len) { - if (repo_get_oid(the_repository, arg.buf, oid)) + if (repo_get_oid_with_flags(the_repository, arg.buf, oid, + GET_OID_SKIP_AMBIGUITY_CHECK)) goto invalid; } else { /* Without -z, an empty value means all zeros: */ @@ -197,7 +198,8 @@ static int parse_next_oid(const char **next, const char *end, *next += arg.len; if (arg.len) { - if (repo_get_oid(the_repository, arg.buf, oid)) + if (repo_get_oid_with_flags(the_repository, arg.buf, oid, + GET_OID_SKIP_AMBIGUITY_CHECK)) goto invalid; } else if (flags & PARSE_SHA1_ALLOW_EMPTY) { /* With -z, treat an empty value as all zeros: */ @@ -772,7 +774,8 @@ int cmd_update_ref(int argc, refname = argv[0]; value = argv[1]; oldval = argv[2]; - if (repo_get_oid(the_repository, value, &oid)) + if (repo_get_oid_with_flags(the_repository, value, &oid, + GET_OID_SKIP_AMBIGUITY_CHECK)) die("%s: not a valid SHA1", value); } @@ -783,7 +786,8 @@ int cmd_update_ref(int argc, * must not already exist: */ oidclr(&oldoid, the_repository->hash_algo); - else if (repo_get_oid(the_repository, oldval, &oldoid)) + else if (repo_get_oid_with_flags(the_repository, oldval, &oldoid, + GET_OID_SKIP_AMBIGUITY_CHECK)) die("%s: not a valid old SHA1", oldval); }
Most of the commands in git-update-ref(1) accept an old and/or new object ID to update a specific reference to. These object IDs get parsed via `repo_get_oid()`, which not only handles plain object IDs, but also those that have a suffix like "~" or "^2". More surprisingly though, it even knows to resolve references, despite the fact that its manpage does not mention this fact even once. One consequence of this is that we also check for ambiguous references: when parsing a full object ID where the DWIM mechanism would also cause us to resolve it as a branch, we'd end up printing a warning. While this check makes sense to have in general, it is arguably less useful in the context of git-update-ref(1). This is out of two reasons: - The manpage is explicitly structured around object IDs. So if we see a fully blown object ID, the intent should be quite clear in general. - The command is part of our plumbing layer and not a tool that users would generally use in interactive workflows. As such, the warning will likely not be visible to anybody in the first place. Furthermore, this check can be quite expensive when updating lots of references via `--stdin`, because we try to read multiple references per object ID that we parse according to the DWIM rules. This effect can be seen both with the "files" and "reftable" backend. The issue is not unique to git-update-ref(1), but was also an issue in git-cat-file(1), where it was addressed by disabling the ambiguity check in 25fba78d36b (cat-file: disable object/refname ambiguity check for batch mode, 2013-07-12). Disable the warning in git-update-ref(1), which provides a significant speedup with both backends. The following benchmark creates 10000 new references with a 100000 preexisting refs with the "files" backend: Benchmark 1: update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD~) Time (mean ± σ): 467.3 ms ± 5.1 ms [User: 100.0 ms, System: 365.1 ms] Range (min … max): 461.9 ms … 479.3 ms 10 runs Benchmark 2: update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD) Time (mean ± σ): 394.1 ms ± 5.8 ms [User: 63.3 ms, System: 327.6 ms] Range (min … max): 384.9 ms … 405.7 ms 10 runs Summary update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD) ran 1.19 ± 0.02 times faster than update-ref: create many refs (refformat = files, preexisting = 100000, new = 10000, revision = HEAD~) And with the "reftable" backend: Benchmark 1: update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD~) Time (mean ± σ): 146.9 ms ± 2.2 ms [User: 90.4 ms, System: 56.0 ms] Range (min … max): 142.7 ms … 150.8 ms 19 runs Benchmark 2: update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD) Time (mean ± σ): 63.2 ms ± 1.1 ms [User: 41.0 ms, System: 21.8 ms] Range (min … max): 61.1 ms … 66.6 ms 41 runs Summary update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD) ran 2.32 ± 0.05 times faster than update-ref: create many refs (refformat = reftable, preexisting = 100000, new = 10000, revision = HEAD~) Note that the absolute improvement with both backends is roughly in the same ballpark, but the relative improvement for the "reftable" backend is more significant because writing the new table to disk is faster in the first place. Signed-off-by: Patrick Steinhardt <ps@pks.im> --- builtin/update-ref.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)