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0cf9b666
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2020-05-12T11:41:44
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tests: merge: fix printf formatter on 32 bit arches
We currently use `PRIuMAX` to print an integer of type `size_t` in
merge::trees::rename::cache_recomputation. While this works just fine on
64 bit arches, it doesn't on 32 bit ones. As a result, our nightly
builds on x86 and arm32 fail.
Fix the issue by using `PRIuZ` instead.
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4dfcc50f
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2020-04-01T15:16:18
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merge: cache negative cache results for similarity metrics
When computing renames, we cache the hash signatures for each of the
potentially conflicting entries so that we do not need to repeatedly
read the file and can at least halfway efficiently determine whether two
files are similar enough to be deemed a rename. In order to make the
hash signatures meaningful, we require at least four lines of data to be
present, resulting in at least four different hashes that can be
compared. Files that are deemed too small are not cached at all and
will thus be repeatedly re-hashed, which is usually not a huge issue.
The issue with above heuristic is in case a file does _not_ have at
least four lines, where a line is anything separated by a consecutive
run of "\n" or "\0" characters. For example "a\nb" is two lines, but
"a\0\0b" is also just two lines. Taken to the extreme, a file that has
megabytes of consecutive space- or NUL-only may also be deemed as too
small and thus not get cached. As a result, we will repeatedly load its
blob, calculate its hash signature just to finally throw it away as we
notice it's not of any value. When you've got a comparitively big file
that you compare against a big set of potentially renamed files, then
the cost simply expodes.
The issue can be trivially fixed by introducing negative cache entries.
Whenever we determine that a given blob does not have a meaningful
representation via a hash signature, we store this negative cache marker
and will from then on not hash it again, but also ignore it as a
potential rename target. This should help the "normal" case already
where you have a lot of small files as rename candidates, but in the
above scenario it's savings are extraordinarily high.
To verify we do not hit the issue anymore with described solution, this
commit adds a test that uses the exact same setup described above with
one 50 megabyte blob of '\0' characters and 1000 other files that get
renamed. Without the negative cache:
$ time ./libgit2_clar -smerge::trees::renames::cache_recomputation >/dev/null
real 11m48.377s
user 11m11.576s
sys 0m35.187s
And with the negative cache:
$ time ./libgit2_clar -smerge::trees::renames::cache_recomputation >/dev/null
real 0m1.972s
user 0m1.851s
sys 0m0.118s
So this represents a ~350-fold performance improvement, but it obviously
depends on how many files you have and how big the blob is. The test
number were chosen in a way that one will immediately notice as soon as
the bug resurfaces.
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e54343a4
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2019-06-29T09:17:32
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fileops: rename to "futils.h" to match function signatures
Our file utils functions all have a "futils" prefix, e.g.
`git_futils_touch`. One would thus naturally guess that their
definitions and implementation would live in files "futils.h" and
"futils.c", respectively, but in fact they live in "fileops.h".
Rename the files to match expectations.
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9994cd3f
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2018-06-25T11:56:52
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treewide: remove use of C++ style comments
C++ style comment ("//") are not specified by the ISO C90 standard and
thus do not conform to it. While libgit2 aims to conform to C90, we did
not enforce it until now, which is why quite a lot of these
non-conforming comments have snuck into our codebase. Do a tree-wide
conversion of all C++ style comments to the supported C style comments
to allow us enforcing strict C90 compliance in a later commit.
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49806e9b
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2017-02-09T16:52:03
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merge_trees: introduce test for submodule renames
Test that shows that submodules are incorrectly considered in renames,
and `git_merge_trees` will fail to lookup the submodule as a blob.
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19ed4d0c
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2017-01-01T22:19:23
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merge: set default rename threshold
When `GIT_MERGE_FIND_RENAMES` is set, provide a default for
`rename_threshold` when it is unset.
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5aa2ac6d
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2014-03-11T22:47:39
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Update git_merge_tree_opts to git_merge_options
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17820381
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2013-11-14T14:05:52
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Rename tests-clar to tests
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