The code to iterate over refs with the reftable backend has seen
some optimization.
* ps/reftable-iteration-perf:
reftable/reader: add comments to `table_iter_next()`
reftable/record: don't try to reallocate ref record name
reftable/block: swap buffers instead of copying
reftable/pq: allocation-less comparison of entry keys
reftable/merged: skip comparison for records of the same subiter
reftable/merged: allocation-less dropping of shadowed records
reftable/record: introduce function to compare records by key
When decoding reftable ref records we first release the pointer to the
record passed to us and then use realloc(3P) to allocate the refname
array. This is a bit misleading though as we know at that point that the
refname will always be `NULL`, so we would always end up allocating a
new char array anyway.
Refactor the code to use `REFTABLE_ALLOC_ARRAY()` instead. As the
following benchmark demonstrates this is a tiny bit more efficient. But
the bigger selling point really is the gained clarity.
Benchmark 1: show-ref: single matching ref (revision = HEAD~)
Time (mean ± σ): 150.1 ms ± 4.1 ms [User: 146.6 ms, System: 3.3 ms]
Range (min … max): 144.5 ms … 180.5 ms 1000 runs
Benchmark 2: show-ref: single matching ref (revision = HEAD)
Time (mean ± σ): 148.9 ms ± 4.5 ms [User: 145.2 ms, System: 3.4 ms]
Range (min … max): 143.0 ms … 185.4 ms 1000 runs
Summary
show-ref: single matching ref (revision = HEAD) ran
1.01 ± 0.04 times faster than show-ref: single matching ref (revision = HEAD~)
Ideally, we should try and reuse the memory of the old record instead of
first freeing and then immediately reallocating it. This requires some
more surgery though and is thus left for a future iteration.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In some places we need to sort reftable records by their keys to
determine their ordering. This is done by first formatting the keys into
a `struct strbuf` and then using `strbuf_cmp()` to compare them. This
logic is needlessly roundabout and can end up costing quite a bit of CPU
cycles, both due to the allocation and formatting logic.
Introduce a new `reftable_record_cmp()` function that knows how to
compare two records with each other without requiring allocations.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
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>
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>
This isn't used per se, but it is useful for debugging, especially
Windows CI failures.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This reduces the amount of glue code, because we don't need a void
pointer or vtable within the structure.
The only snag is that reftable_index_record contain a strbuf, so it
cannot be zero-initialized. To address this, use reftable_new_record()
to return fresh instance, given a record type. Since
reftable_new_record() doesn't cause heap allocation anymore, it should
be balanced with reftable_record_release() rather than
reftable_record_destroy().
Thanks to Peff for the suggestion.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This simplifies unittests a little, and provides further coverage for
reftable_record_copy().
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The reftable format is structured as a sequence of blocks, and each block
contains a sequence of prefix-compressed key-value records. There are 4 types of
records, and they have similarities in how they must be handled. This is
achieved by introducing a polymorphic 'record' type that encapsulates ref, log,
index and object records.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
