According to our usual coding style, the `reftable_new_record()`
function would indicate that it is allocating a new record. This is not
the case though as the function merely initializes records without
allocating any memory.
Replace `reftable_new_record()` with a new `reftable_record_init()`
function that takes a record pointer as input and initializes it
accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Refactor the initialization of the merged iterator to fit our code style
better. This refactoring prepares the code for a refactoring of how
records are being initialized.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code to seek reftable records in the merged table code is quite hard
to read and does not conform to our coding style in multiple ways:
- We have multiple exit paths where we release resources even though
that is not really necessary.
- We use a scoped error variable `e` which is hard to reason about.
This variable is not required at all.
- We allocate memory in the variable declarations, which is easy to
miss.
Refactor the function so that it becomes more maintainable in the
future.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
While the stack length is already stored as `size_t`, we frequently use
`int`s to refer to those stacks throughout the reftable library. Convert
those cases to use `size_t` instead to make things consistent.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We use `int`s to track reftable slices when compacting the reftable
stack, which is considered to be a code smell in the Git project.
Convert the code to use `size_t` instead.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We use `int`s to index into arrays of segments and track the length of
them, which is considered to be a code smell in the Git project. Convert
the code to use `size_t` instead.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `stack_compact_range()` function receives a "first" and "last" index
that indicates which tables of the reftable stack should be compacted.
Naturally, "first" must be smaller than "last" in order to identify a
proper range of tables to compress, which we indeed also assert in the
function. But the validations happens after we have already allocated
arrays with a size of `last - first + 1`, leading to an underflow and
thus an invalid allocation size.
Fix this by reordering the array allocations to happen after we have
validated parameters. While at it, convert the array allocations to use
the newly introduced macros.
Note that the relevant variables pointing into arrays should also be
converted to use `size_t` instead of `int`. This is left for a later
commit in this series.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar to the preceding commit, let's carry over macros to allocate
arrays with `REFTABLE_ALLOC_ARRAY()` and `REFTABLE_CALLOC_ARRAY()`. This
requires us to change the signature of `reftable_calloc()`, which only
takes a single argument right now and thus puts the burden on the caller
to calculate the final array's size. This is a net improvement though as
it means that we can now provide proper overflow checks when multiplying
the array size with the member size.
Convert callsites of `reftable_calloc()` to the new signature and start
using the new macros where possible.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Throughout the reftable library we have many cases where we need to grow
arrays. In order to avoid too many reallocations, we roughly double the
capacity of the array on each iteration. The resulting code pattern is
duplicated across many sites.
We have similar patterns in our main codebase, which is why we have
eventually introduced an `ALLOC_GROW()` macro to abstract it away and
avoid some code duplication. We cannot easily reuse this macro here
though because `ALLOC_GROW()` uses `REALLOC_ARRAY()`, which in turn will
call realloc(3P) to grow the array. The reftable code is structured as a
library though (even if the boundaries are fuzzy), and one property this
brings with it is that it is possible to plug in your own allocators. So
instead of using realloc(3P), we need to use `reftable_realloc()` that
knows to use the user-provided implementation.
So let's introduce two new macros `REFTABLE_REALLOC_ARRAY()` and
`REFTABLE_ALLOC_GROW()` that mirror what we do in our main codebase,
with two modifications:
- They use `reftable_realloc()`, as explained above.
- They use a different growth factor of `2 * cap + 1` instead of `(cap
+ 16) * 3 / 2`.
The second change is because we know a bit more about the allocation
patterns in the reftable library. In most cases, we end up only having a
handful of items in the array and don't end up growing them. The initial
capacity that our normal growth factor uses (which is 24) would thus end
up over-allocating in a lot of code paths. This effect is measurable:
- Before change:
HEAP SUMMARY:
in use at exit: 671,983 bytes in 152 blocks
total heap usage: 3,843,446 allocs, 3,843,294 frees, 223,761,402 bytes allocated
- After change with a growth factor of `(2 * alloc + 1)`:
HEAP SUMMARY:
in use at exit: 671,983 bytes in 152 blocks
total heap usage: 3,843,446 allocs, 3,843,294 frees, 223,761,410 bytes allocated
- After change with a growth factor of `(alloc + 16)* 2 / 3`:
HEAP SUMMARY:
in use at exit: 671,983 bytes in 152 blocks
total heap usage: 3,833,673 allocs, 3,833,521 frees, 4,728,251,742 bytes allocated
While the total heap usage is roughly the same, we do end up allocating
significantly more bytes with our usual growth factor (in fact, roughly
21 times as many).
Convert the reftable library to use these new macros.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Low-level I/O optimization for reftable.
* ps/reftable-optimize-io:
reftable/stack: fix race in up-to-date check
reftable/stack: unconditionally reload stack after commit
reftable/blocksource: use mmap to read tables
reftable/blocksource: refactor code to match our coding style
reftable/stack: use stat info to avoid re-reading stack list
reftable/stack: refactor reloading to use file descriptor
reftable/stack: refactor stack reloading to have common exit path
In 6fdfaf15a0 (reftable/stack: use stat info to avoid re-reading stack
list, 2024-01-11) we have introduced a new mechanism to avoid re-reading
the table list in case stat(3P) figures out that the stack didn't change
since the last time we read it.
While this change significantly improved performance when writing many
refs, it can unfortunately lead to false negatives in very specific
scenarios. Given two processes A and B, there is a feasible sequence of
events that cause us to accidentally treat the table list as up-to-date
even though it changed:
1. A reads the reftable stack and caches its stat info.
2. B updates the stack, appending a new table to "tables.list". This
will both use a new inode and result in a different file size, thus
invalidating A's cache in theory.
3. B decides to auto-compact the stack and merges two tables. The file
size now matches what A has cached again. Furthermore, the
filesystem may decide to recycle the inode number of the file we
have replaced in (2) because it is not in use anymore.
4. A reloads the reftable stack. Neither the inode number nor the
file size changed. If the timestamps did not change either then we
think the cached copy of our stack is up-to-date.
In fact, the commit introduced three related issues:
- Non-POSIX compliant systems may not report proper `st_dev` and
`st_ino` values in stat(3P), which made us rely solely on the
file's potentially coarse-grained mtime and ctime.
- `stat_validity_check()` and friends may end up not comparing
`st_dev` and `st_ino` depending on the "core.checkstat" config,
again reducing the signal to the mtime and ctime.
- `st_ino` can be recycled, rendering the check moot even on
POSIX-compliant systems.
Given that POSIX defines that "The st_ino and st_dev fields taken
together uniquely identify the file within the system", these issues led
to the most important signal to establish file identity to be ignored or
become useless in some cases.
Refactor the code to stop using `stat_validity_check()`. Instead, we
manually stat(3P) the file descriptors to make relevant information
available. On Windows and MSYS2 the result will have both `st_dev` and
`st_ino` set to 0, which allows us to address the first issue by not
using the stat-based cache in that case. It also allows us to make sure
that we always compare `st_dev` and `st_ino`, addressing the second
issue.
The third issue of inode recycling can be addressed by keeping the file
descriptor of "files.list" open during the lifetime of the reftable
stack. As the file will still exist on disk even though it has been
unlinked it is impossible for its inode to be recycled as long as the
file descriptor is still open.
This should address the race in a POSIX-compliant way. The only real
downside is that this mechanism cannot be used on non-POSIX-compliant
systems like Windows. But we at least have the second-level caching
mechanism in place that compares contents of "files.list" with the
currently loaded list of tables.
This new mechanism performs roughly the same as the previous one that
relied on `stat_validity_check()`:
Benchmark 1: update-ref: create many refs (HEAD~)
Time (mean ± σ): 4.754 s ± 0.026 s [User: 2.204 s, System: 2.549 s]
Range (min … max): 4.694 s … 4.802 s 20 runs
Benchmark 2: update-ref: create many refs (HEAD)
Time (mean ± σ): 4.721 s ± 0.020 s [User: 2.194 s, System: 2.527 s]
Range (min … max): 4.691 s … 4.753 s 20 runs
Summary
update-ref: create many refs (HEAD~) ran
1.01 ± 0.01 times faster than update-ref: create many refs (HEAD)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
After we have committed an addition to the reftable stack we call
`reftable_stack_reload()` to reload the stack and thus reflect the
changes that were just added. This function will only conditionally
reload the stack in case `stack_uptodate()` tells us that the stack
needs reloading. This check is wasteful though because we already know
that the stack needs reloading.
Call `reftable_stack_reload_maybe_reuse()` instead, which will
unconditionally reload the stack. This is merely a conceptual fix, the
code in question was not found to cause any problems in practice.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
More fixes and optimizations to the reftable backend.
* ps/reftable-fixes-and-optims:
reftable/merged: transfer ownership of records when iterating
reftable/merged: really reuse buffers to compute record keys
reftable/record: store "val2" hashes as static arrays
reftable/record: store "val1" hashes as static arrays
reftable/record: constify some parts of the interface
reftable/writer: fix index corruption when writing multiple indices
reftable/stack: do not auto-compact twice in `reftable_stack_add()`
reftable/stack: do not overwrite errors when compacting
The blocksource interface provides an interface to read blocks from a
reftable table. This interface is implemented using read(3P) calls on
the underlying file descriptor. While this works alright, this pattern
is very inefficient when repeatedly querying the reftable stack for one
or more refs. This inefficiency can mostly be attributed to the fact
that we often need to re-read the same blocks over and over again, and
every single time we need to call read(3P) again.
A natural fit in this context is to use mmap(3P) instead of read(3P),
which has a bunch of benefits:
- We do not need to come up with a caching strategy for some of the
blocks as this will be handled by the kernel already.
- We can avoid the overhead of having to call into the read(3P)
syscall repeatedly.
- We do not need to allocate returned blocks repeatedly, but can
instead hand out pointers into the mmapped region directly.
Using mmap comes with a significant drawback on Windows though, because
mmapped files cannot be deleted and neither is it possible to rename
files onto an mmapped file. But for one, the reftable library gracefully
handles the case where auto-compaction cannot delete a still-open stack
already and ignores any such errors. Also, `reftable_stack_clean()` will
prune stale tables which are not referenced by "tables.list" anymore so
that those files can eventually be pruned. And second, we never rewrite
already-written stacks, so it does not matter that we cannot rename a
file over an mmaped file, either.
Another unfortunate property of mmap is that it is not supported by all
systems. But given that the size of reftables should typically be rather
limited (megabytes at most in the vast majority of repositories), we can
use the fallback implementation provided by `git_mmap()` which reads the
whole file into memory instead. This is the same strategy that the
"packed" backend uses.
While this change doesn't significantly improve performance in the case
where we're seeking through stacks once (like e.g. git-for-each-ref(1)
would). But it does speed up usecases where there is lots of random
access to refs, e.g. when writing. The following benchmark demonstrates
these savings with git-update-ref(1) creating N refs in an otherwise
empty repository:
Benchmark 1: update-ref: create many refs (refcount = 1, revision = HEAD~)
Time (mean ± σ): 5.1 ms ± 0.2 ms [User: 2.5 ms, System: 2.5 ms]
Range (min … max): 4.8 ms … 7.1 ms 111 runs
Benchmark 2: update-ref: create many refs (refcount = 100, revision = HEAD~)
Time (mean ± σ): 14.8 ms ± 0.5 ms [User: 7.1 ms, System: 7.5 ms]
Range (min … max): 14.1 ms … 18.7 ms 84 runs
Benchmark 3: update-ref: create many refs (refcount = 10000, revision = HEAD~)
Time (mean ± σ): 926.4 ms ± 5.6 ms [User: 448.5 ms, System: 477.7 ms]
Range (min … max): 920.0 ms … 936.1 ms 10 runs
Benchmark 4: update-ref: create many refs (refcount = 1, revision = HEAD)
Time (mean ± σ): 5.0 ms ± 0.2 ms [User: 2.4 ms, System: 2.5 ms]
Range (min … max): 4.7 ms … 5.4 ms 111 runs
Benchmark 5: update-ref: create many refs (refcount = 100, revision = HEAD)
Time (mean ± σ): 10.5 ms ± 0.2 ms [User: 5.0 ms, System: 5.3 ms]
Range (min … max): 10.0 ms … 10.9 ms 93 runs
Benchmark 6: update-ref: create many refs (refcount = 10000, revision = HEAD)
Time (mean ± σ): 529.6 ms ± 9.1 ms [User: 268.0 ms, System: 261.4 ms]
Range (min … max): 522.4 ms … 547.1 ms 10 runs
Summary
update-ref: create many refs (refcount = 1, revision = HEAD) ran
1.01 ± 0.06 times faster than update-ref: create many refs (refcount = 1, revision = HEAD~)
2.08 ± 0.07 times faster than update-ref: create many refs (refcount = 100, revision = HEAD)
2.95 ± 0.14 times faster than update-ref: create many refs (refcount = 100, revision = HEAD~)
105.33 ± 3.76 times faster than update-ref: create many refs (refcount = 10000, revision = HEAD)
184.24 ± 5.89 times faster than update-ref: create many refs (refcount = 10000, revision = HEAD~)
Theoretically, we could also replicate the strategy of the "packed"
backend where small tables are read into memory instead of using mmap.
Benchmarks did not confirm that this has a performance benefit though.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Refactor `reftable_block_source_from_file()` to match our coding style
better.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Whenever we call into the refs interfaces we potentially have to reload
refs in case they have been concurrently modified, either in-process or
externally. While this happens somewhat automatically for loose refs
because we simply try to re-read the files, the "packed" backend will
reload its snapshot of the packed-refs file in case its stat info has
changed since last reading it.
In the reftable backend we have a similar mechanism that is provided by
`reftable_stack_reload()`. This function will read the list of stacks
from "tables.list" and, if they have changed from the currently stored
list, reload the stacks. This is heavily inefficient though, as we have
to check whether the stack is up-to-date on basically every read and
thus keep on re-reading the file all the time even if it didn't change
at all.
We can do better and use the same stat(3P)-based mechanism that the
"packed" backend uses. Instead of reading the file, we will only open
the file descriptor, fstat(3P) it, and then compare the info against the
cached value from the last time we have updated the stack. This should
always work alright because "tables.list" is updated atomically via a
rename, so even if the ctime or mtime wasn't granular enough to identify
a change, at least the inode number or file size should have changed.
This change significantly speeds up operations where many refs are read,
like when using git-update-ref(1). The following benchmark creates N
refs in an otherwise-empty repository via `git update-ref --stdin`:
Benchmark 1: update-ref: create many refs (refcount = 1, revision = HEAD~)
Time (mean ± σ): 5.1 ms ± 0.2 ms [User: 2.4 ms, System: 2.6 ms]
Range (min … max): 4.8 ms … 7.2 ms 109 runs
Benchmark 2: update-ref: create many refs (refcount = 100, revision = HEAD~)
Time (mean ± σ): 19.1 ms ± 0.9 ms [User: 8.9 ms, System: 9.9 ms]
Range (min … max): 18.4 ms … 26.7 ms 72 runs
Benchmark 3: update-ref: create many refs (refcount = 10000, revision = HEAD~)
Time (mean ± σ): 1.336 s ± 0.018 s [User: 0.590 s, System: 0.724 s]
Range (min … max): 1.314 s … 1.373 s 10 runs
Benchmark 4: update-ref: create many refs (refcount = 1, revision = HEAD)
Time (mean ± σ): 5.1 ms ± 0.2 ms [User: 2.4 ms, System: 2.6 ms]
Range (min … max): 4.8 ms … 7.2 ms 109 runs
Benchmark 5: update-ref: create many refs (refcount = 100, revision = HEAD)
Time (mean ± σ): 14.8 ms ± 0.2 ms [User: 7.1 ms, System: 7.5 ms]
Range (min … max): 14.2 ms … 15.2 ms 82 runs
Benchmark 6: update-ref: create many refs (refcount = 10000, revision = HEAD)
Time (mean ± σ): 927.6 ms ± 5.3 ms [User: 437.8 ms, System: 489.5 ms]
Range (min … max): 919.4 ms … 936.4 ms 10 runs
Summary
update-ref: create many refs (refcount = 1, revision = HEAD) ran
1.00 ± 0.07 times faster than update-ref: create many refs (refcount = 1, revision = HEAD~)
2.89 ± 0.14 times faster than update-ref: create many refs (refcount = 100, revision = HEAD)
3.74 ± 0.25 times faster than update-ref: create many refs (refcount = 100, revision = HEAD~)
181.26 ± 8.30 times faster than update-ref: create many refs (refcount = 10000, revision = HEAD)
261.01 ± 12.35 times faster than update-ref: create many refs (refcount = 10000, revision = HEAD~)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We're about to introduce a stat(3P)-based caching mechanism to reload
the list of stacks only when it has changed. In order to avoid race
conditions this requires us to have a file descriptor available that we
can use to call fstat(3P) on.
Prepare for this by converting the code to use `fd_read_lines()` so that
we have the file descriptor readily available.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `reftable_stack_reload_maybe_reuse()` function is responsible for
reloading the reftable list from disk. The function is quite hard to
follow though because it has a bunch of different exit paths, many of
which have to free the same set of resources.
Refactor the function to have a common exit path. While at it, touch up
the style of this function a bit to match our usual coding style better.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remove unused header "#include".
* en/header-cleanup:
treewide: remove unnecessary includes in source files
treewide: add direct includes currently only pulled in transitively
trace2/tr2_tls.h: remove unnecessary include
submodule-config.h: remove unnecessary include
pkt-line.h: remove unnecessary include
line-log.h: remove unnecessary include
http.h: remove unnecessary include
fsmonitor--daemon.h: remove unnecessary includes
blame.h: remove unnecessary includes
archive.h: remove unnecessary include
treewide: remove unnecessary includes in source files
treewide: remove unnecessary includes from header files
When iterating over records with the merged iterator we put the records
into a priority queue before yielding them to the caller. This means
that we need to allocate the contents of these records before we can
pass them over to the caller.
The handover to the caller is quite inefficient though because we first
deallocate the record passed in by the caller and then copy over the new
record, which requires us to reallocate memory.
Refactor the code to instead transfer ownership of the new record to the
caller. So instead of reallocating all contents, we now release the old
record and then copy contents of the new record into place.
The following benchmark of `git show-ref --quiet` in a repository with
around 350k refs shows a clear improvement. Before:
HEAP SUMMARY:
in use at exit: 21,163 bytes in 193 blocks
total heap usage: 708,058 allocs, 707,865 frees, 36,783,255 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 21,163 bytes in 193 blocks
total heap usage: 357,007 allocs, 356,814 frees, 24,193,602 bytes allocated
This shows that we now have roundabout a single allocation per record
that we're yielding from the iterator. Ideally, we'd also get rid of
this allocation so that the number of allocations doesn't scale with the
number of refs anymore. This would require some larger surgery though
because the memory is owned by the priority queue before transferring it
over to the caller.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 829231dc20 (reftable/merged: reuse buffer to compute record keys,
2023-12-11), we have refactored the merged iterator to reuse a pair of
long-living strbufs by relying on the fact that `reftable_record_key()`
tries to reuse already allocated strbufs by calling `strbuf_reset()`,
which should give us significantly fewer reallocations compared to the
old code that used on-stack strbufs that are allocated for each and
every iteration. Unfortunately, we called `strbuf_release()` on these
long-living strbufs that we meant to reuse on each iteration, defeating
the optimization.
Fix this performance issue by not releasing those buffers on iteration
anymore, where we instead rely on `merged_iter_close()` to release the
buffers for us.
Using `git show-ref --quiet` in a repository with ~350k refs this leads
to a significant drop in allocations. Before:
HEAP SUMMARY:
in use at exit: 21,163 bytes in 193 blocks
total heap usage: 1,410,148 allocs, 1,409,955 frees, 61,976,068 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 21,163 bytes in 193 blocks
total heap usage: 708,058 allocs, 707,865 frees, 36,783,255 bytes allocated
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar to the preceding commit, convert ref records of type "val2" to
store their object IDs in static arrays instead of allocating them for
every single record.
We're using the same benchmark as in the preceding commit, with `git
show-ref --quiet` in a repository with ~350k refs. This time around
though the effects aren't this huge. Before:
HEAP SUMMARY:
in use at exit: 21,163 bytes in 193 blocks
total heap usage: 1,419,040 allocs, 1,418,847 frees, 62,153,868 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 21,163 bytes in 193 blocks
total heap usage: 1,410,148 allocs, 1,409,955 frees, 61,976,068 bytes allocated
This is because "val2"-type records are typically only stored for peeled
tags, and the number of annotated tags in the benchmark repository is
rather low. Still, it can be seen that this change leads to a reduction
of allocations overall, even if only a small one.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When reading ref records of type "val1", we store its object ID in an
allocated array. This results in an additional allocation for every
single ref record we read, which is rather inefficient especially when
iterating over refs.
Refactor the code to instead use an embedded array of `GIT_MAX_RAWSZ`
bytes. While this means that `struct ref_record` is bigger now, we
typically do not store all refs in an array anyway and instead only
handle a limited number of records at the same point in time.
Using `git show-ref --quiet` in a repository with ~350k refs this leads
to a significant drop in allocations. Before:
HEAP SUMMARY:
in use at exit: 21,098 bytes in 192 blocks
total heap usage: 2,116,683 allocs, 2,116,491 frees, 76,098,060 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 21,098 bytes in 192 blocks
total heap usage: 1,419,031 allocs, 1,418,839 frees, 62,145,036 bytes allocated
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We're about to convert reftable records to stop storing their object IDs
as allocated hashes. Prepare for this refactoring by constifying some
parts of the interface that will be impacted by this.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Each reftable may contain multiple types of blocks for refs, objects and
reflog records, where each of these may have an index that makes it more
efficient to find the records. It was observed that the index for log
records can become corrupted under certain circumstances, where the
first entry of the index points into the object index instead of to the
log records.
As it turns out, this corruption can occur whenever we write a log index
as well as at least one additional index. Writing records and their index
is basically a two-step process:
1. We write all blocks for the corresponding record. Each block that
gets written is added to a list of blocks to index.
2. Once all blocks were written we finish the section. If at least two
blocks have been added to the list of blocks to index then we will
now write the index for those blocks and flush it, as well.
When we have a very large number of blocks then we may decide to write a
multi-level index, which is why we also keep track of the list of the
index blocks in the same way as we previously kept track of the blocks
to index.
Now when we have finished writing all index blocks we clear the index
and flush the last block to disk. This is done in the wrong order though
because flushing the block to disk will re-add it to the list of blocks
to be indexed. The result is that the next section we are about to write
will have an entry in the list of blocks to index that points to the
last block of the preceding section's index, which will corrupt the log
index.
Fix this corruption by clearing the index after having written the last
block.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 5c086453ff (reftable/stack: perform auto-compaction with
transactional interface, 2023-12-11), we fixed a bug where the
transactional interface to add changes to a reftable stack did not
perform auto-compaction by calling `reftable_stack_auto_compact()` in
`reftable_stack_addition_commit()`. While correct, this change may now
cause us to perform auto-compaction twice in the non-transactional
interface `reftable_stack_add()`:
- It performs auto-compaction by itself.
- It now transitively performs auto-compaction via the transactional
interface.
Remove the first instance so that we only end up doing auto-compaction
once.
Reported-by: Han-Wen Nienhuys <hanwenn@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In order to compact multiple stacks we iterate through the merged ref
and log records. When there is any error either when reading the records
from the old merged table or when writing the records to the new table
then we break out of the respective loops. When breaking out of the loop
for the ref records though the error code will be overwritten, which may
cause us to inadvertently skip over bad ref records. In the worst case,
this can lead to a compacted stack that is missing records.
Fix the code by using `goto done` instead so that any potential error
codes are properly returned to the caller.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Each of these were checked with
gcc -E -I. ${SOURCE_FILE} | grep ${HEADER_FILE}
to ensure that removing the direct inclusion of the header actually
resulted in that header no longer being included at all (i.e. that
no other header pulled it in transitively).
...except for a few cases where we verified that although the header
was brought in transitively, nothing from it was directly used in
that source file. These cases were:
* builtin/credential-cache.c
* builtin/pull.c
* builtin/send-pack.c
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When iterating over entries in the block iterator we compute the key of
each of the entries and write it into a buffer. We do not reuse the
buffer though and thus re-allocate it on every iteration, which is
wasteful.
Refactor the code to reuse the buffer.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are a bunch of locations where we initialize members of `struct
block_iter`, which makes it harder than necessary to expand this struct
to have additional members. Unify the logic via a new `BLOCK_ITER_INIT`
macro that initializes all members.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When iterating over entries in the merged iterator's queue, we compute
the key of each of the entries and write it into a buffer. We do not
reuse the buffer though and thus re-allocate it on every iteration,
which is wasteful given that we never transfer ownership of the
allocated bytes outside of the loop.
Refactor the code to reuse the buffer. This also fixes a potential
memory leak when `merged_iter_advance_subiter()` returns an error.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing a new reftable stack, Git will first create the stack with
a random suffix so that concurrent updates will not try to write to the
same file. This random suffix is computed via a call to rand(3P). But we
never seed the function via srand(3P), which means that the suffix is in
fact always the same.
Fix this bug by using `git_rand()` instead, which does not need to be
initialized. While this function is likely going to be slower depending
on the platform, this slowness should not matter in practice as we only
use it when writing a new reftable stack.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When starting a transaction via `reftable_stack_init_addition()`, we
create a lockfile for the reftable stack itself which we'll write the
new list of tables to. But if we terminate abnormally e.g. via a call to
`die()`, then we do not remove the lockfile. Subsequent executions of
Git which try to modify references will thus fail with an out-of-date
error.
Fix this bug by registering the lock as a `struct tempfile`, which
ensures automatic cleanup for us.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In `reftable_stack_reload_once()` we iterate over all the tables added
to the stack in order to figure out whether any of the tables needs to
be reloaded. We use a set of buffers in this context to compute the
paths of these tables, but discard those buffers on every iteration.
This is quite wasteful given that we do not need to transfer ownership
of the allocated buffer outside of the loop.
Refactor the code to instead reuse the buffers to reduce the number of
allocations we need to do. Note that we do not have to manually reset
the buffer because `stack_filename()` does this for us already.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Whenever updating references or reflog entries in the reftable stack, we
need to add a new table to the stack, thus growing the stack's length by
one. The stack can grow to become quite long rather quickly, leading to
performance issues when trying to read records. But besides performance
issues, this can also lead to exhaustion of file descriptors very
rapidly as every single table requires a separate descriptor when
opening the stack.
While git-pack-refs(1) fixes this issue for us by merging the tables, it
runs too irregularly to keep the length of the stack within reasonable
limits. This is why the reftable stack has an auto-compaction mechanism:
`reftable_stack_add()` will call `reftable_stack_auto_compact()` after
its added the new table, which will auto-compact the stack as required.
But while this logic works alright for `reftable_stack_add()`, we do not
do the same in `reftable_addition_commit()`, which is the transactional
equivalent to the former function that allows us to write multiple
updates to the stack atomically. Consequentially, we will easily run
into file descriptor exhaustion in code paths that use many separate
transactions like e.g. non-atomic fetches.
Fix this issue by calling `reftable_stack_auto_compact()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
While we have several tests that check whether we correctly perform
auto-compaction when manually calling `reftable_stack_auto_compact()`,
we don't have any tests that verify whether `reftable_stack_add()` does
call it automatically. Add one.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are calls to write(3P) where we don't properly handle interrupts.
Convert them to use `write_in_full()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are calls to pread(3P) and read(3P) where we don't properly handle
interrupts. Convert them to use `pread_in_full()` and `read_in_full()`,
respectively.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `EXPECT` macros used by the reftable test framework are all using a
single `if` statement with the actual condition. This results in weird
syntax when using them in if/else statements like the following:
```
if (foo)
EXPECT(foo == 2)
else
EXPECT(bar == 2)
```
Note that there need not be a trailing semicolon. Furthermore, it is not
immediately obvious whether the else now belongs to the `if (foo)` or
whether it belongs to the expanded `if (foo == 2)` from the macro.
Fix this by wrapping the macros in a do/while loop.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
hash.h depends upon and includes repository.h, due to the definition and
use of the_hash_algo (defined as the_repository->hash_algo). However,
most headers trying to include hash.h are only interested in the layout
of the structs like object_id. Move the parts of hash.h that do not
depend upon repository.h into a new file hash-ll.h (the "low level"
parts of hash.h), and adjust other files to use this new header where
the convenience inline functions aren't needed.
This allows hash.h and object.h to be fairly small, minimal headers. It
also exposes a lot of hidden dependencies on both path.h (which was
brought in by repository.h) and repository.h (which was previously
implicitly brought in by object.h), so also adjust other files to be
more explicit about what they depend upon.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The speed of the merged_iter_pqueue_add() can be improved by using a
pointer to the pq_entry struct, which is 96 bytes. Since the pq_entry
param is worked directly on the stack and does not currently have a
pointer to it, the merged_iter_pqueue_add() function is slightly
slower.
References to pq_entry in reftable have typically included pointers,
such as both of the params for pq_less().
Since we are working with pointers in the pq_entry param, as keenly
pointed out, the pq_entry param has also been made into a const since
the contents of the pq_entry param are copied and not manipulated.
Signed-off-by: Elijah Conners <business@elijahpepe.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The reader code passes around a "struct reftable_reader" context
variable. But the seek function doesn't need it; the table iterator we
already get is sufficient.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce and apply coccinelle rule to discourage an explicit
comparison between a pointer and NULL, and applies the clean-up to
the maintenance track.
* ep/maint-equals-null-cocci:
tree-wide: apply equals-null.cocci
tree-wide: apply equals-null.cocci
contrib/coccinnelle: add equals-null.cocci
1214aa841b (reftable: add blocksource, an abstraction for random
access reads, 2021-10-07), makes the assumption that it is ok to
free a reftable_block pointing to NULL if the size is also set to
0, but implements that using a memset call that at least in glibc
based system will trigger a runtime exception if called with a
NULL pointer as its first parameter.
Avoid doing so by adding a conditional to check for the size in all
three identically looking functions that were affected, and therefore,
still allow memset to help catch callers that might incorrectly pass
a NULL pointer with a non zero size, but avoiding the exception for
the valid cases.
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change the assignment syntax introduced in 66c0dabab5 (reftable: make
reftable_record a tagged union, 2022-01-20) to be portable to AIX xlc
v12.1:
avar@gcc111:[/home/avar]xlc -qversion
IBM XL C/C++ for AIX, V12.1 (5765-J02, 5725-C72)
Version: 12.01.0000.0000
The error emitted before this was e.g.:
"reftable/generic.c", line 133.26: 1506-196 (S) Initialization
between types "char*" and "struct reftable_ref_record" is not
allowed.
The syntax in the pre-image is supported by e.g. xlc 13.01 on a newer
AIX version:
avar@gcc119:[/home/avar]xlc -qversion
IBM XL C/C++ for AIX, V13.1.3 (5725-C72, 5765-J07)
Version: 13.01.0003.0006
But as we've otherwise supported this compiler let's not break it
entirely if it's easy to work around it.
Suggested-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This function is part of the reftable API, so it should use the
reftable_ prefix
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The ID => ref map is trimming object IDs to a disambiguating prefix.
Check that we are computing their length correctly.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
