Replace throwing `protocol_exception` with returning it as a result
or an exceptional future in the transport server module. The goal is
to improve performance.
Most of the `protocol_exception` throws were made from
`fragmented_temporary_buffer` module, by passing `exception_thrower()`
to its `read*` methods. `fragmented_temporary_buffer` is changed so
that it now accepts an exception creator, not exception thrower.
`fragmented_temporary_buffer_concepts::ExceptionCreator` concept replaced
`fragmented_temporary_buffer_concepts::ExceptionThrower` and all
methods that have been throwing now return failed result of type
`utils::result_with_exception_ptr`. This change is then propagated to the callers.
The scope of this patch is `protocol_exception`, so commitlog just calls
`.value()` method on the result. If the result failed, that will throw the
exception from the result, as defined by `utils::result_with_exception_ptr_throw_policy`.
This means that the behavior of commitlog module stays the same.
transport server module handles results gracefully. All the caller functions
that return non-future value `T` now return `utils::result_with_exception_ptr<T>`.
When the caller is a function that returns a future, and it receives
failed result, `make_exception_future(std::move(failed_result).value())`
is returned. The rest of the callstack up to the transport server `handle_error`
function is already working without throwing, and that's how zero throws is
achieved.
Fixes: #24567
C++20 introduced two new attributes--likely and unlikely--that
function as a built-in replacement for __builtin_expect implemented
in various compilers. Since it makes code easier to read and it's
an integral part of the language, there's no reason to not use it
instead.
Closesscylladb/scylladb#24786
The later includes the former and in addition to `seastar::format()`,
`print.hh` also provides helpers like `seastar::fprint()` and
`seastar::print()`, which are deprecated and not used by scylladb.
Previously, we include `seastar/core/print.hh` for using
`seastar::format()`. and in seastar 5b04939e, we extracted
`seastar::format()` into `seastar/core/format.hh`. this allows us
to include a much smaller header.
In this change, we just include `seastar/core/format.hh` in place of
`seastar/core/print.hh`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#21574
Currently, parsers work with temporary_buffer<char>. This is unsafe
when invoked by bsearch_clustered_cursor, which reuses some of the
parsers, and passes temporary_buffer<char> which is a view onto LSA
buffer which comes from the index file page cache. This view is stable
only around consume(). If parsing requires more than one page, it will
continue with a different input buffer. The old buffer will be
invalid, and it's unsafe for the parser to store and access
it. Unfortunetly, the temporary_buffer API allows sharing the buffer
via the share() method, which shares the underlying memory area. This
is not correct when the underlying is managed by LSA, because storage
may move. Parser uses this sharing when parsing blobs, e.g. clustering
key components. When parsing resumes in the next page, parser will try
to access the stored shared buffers pointing to the previous page,
which may result in use-after-free on the memory area.
In prearation for fixing the problem, parametrize parsers to work with
different kinds of buffers. This will allow us to instantiate them
with a buffer kind which supports sharing of LSA buffers properly in a
safe way.
It's not purely mechanical work. Some parts of the parsing state
machine still works with temporary_buffer<char>, and allocate buffers
internally, when reading into linearized destination buffer. They used
to store this destination in _read_bytes vector, same field which is
used to store the shared buffers. Now it's not possible, since shared
buffer type may be different than temporary_buffer<char>. So those
paths were changed to use a new field: _read_bytes_buf.
in C++20, compiler generate operator!=() if the corresponding
operator==() is already defined, the language now understands
that the comparison is symmetric in the new standard.
fortunately, our operator!=() is always equivalent to
`! operator==()`, this matches the behavior of the default
generated operator!=(). so, in this change, all `operator!=`
are removed.
in addition to the defaulted operator!=, C++20 also brings to us
the defaulted operator==() -- it is able to generated the
operator==() if the member-wise lexicographical comparison.
under some circumstances, this is exactly what we need. so,
in this change, if the operator==() is also implemented as
a lexicographical comparison of all memeber variables of the
class/struct in question, it is implemented using the default
generated one by removing its body and mark the function as
`default`. moreover, if the class happen to have other comparison
operators which are implemented using lexicographical comparison,
the default generated `operator<=>` is used in place of
the defaulted `operator==`.
sometimes, we fail to mark the operator== with the `const`
specifier, in this change, to fulfil the need of C++ standard,
and to be more correct, the `const` specifier is added.
also, to generate the defaulted operator==, the operand should
be `const class_name&`, but it is not always the case, in the
class of `version`, we use `version` as the parameter type, to
fulfill the need of the C++ standard, the parameter type is
changed to `const version&` instead. this does not change
the semantic of the comparison operator. and is a more idiomatic
way to pass non-trivial struct as function parameters.
please note, because in C++20, both operator= and operator<=> are
symmetric, some of the operators in `multiprecision` are removed.
they are the symmetric form of the another variant. if they were
not removed, compiler would, for instance, find ambiguous
overloaded operator '=='.
this change is a cleanup to modernize the code base with C++20
features.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13687
Large contiguous buffers put large pressure on the allocator
and are a common source of reactor stalls. Therefore, Scylla avoids
their use, replacing it with fragmented buffers whenever possible.
However, the use of large contiguous buffers is impossible to avoid
when dealing with some external libraries (i.e. some compression
libraries, like LZ4).
Fortunately, calls to external libraries are synchronous, so we can
minimize the allocator impact by reusing a single buffer between calls.
An implementation of such a reusable buffer has two conflicting goals:
to allocate as rarely as possible, and to waste as little memory as
possible. The bigger the buffer, the more likely that it will be able
to handle future requests without reallocation, but also the memory
memory it ties up.
If request sizes are repetitive, the near-optimal solution is to
simply resize the buffer up to match the biggest seen request,
and never resize down.
However, if we anticipate pathologically large requests, which are
caused by an application/configuration bug and are never repeated
again after they are fixed, we might want to resize down after such
pathological requests stop, so that the memory they took isn't tied
up forever.
The current implementation of reusable buffers handles this by
resizing down to 0 every 100'000 requests.
This patch attempts to solve a few shortcomings of the current
implementation.
1. Resizing to 0 is too aggressive. During regular operation, we will
surely need to resize it back to the previous size again. If something
is allocated in the hole left by the old buffer, this might cause
a stall. We prefer to resize down only after pathological requests.
2. When resizing, the current implementation allocates the new buffer
before freeing the old one. This increases allocator pressure for no
reason.
3. When resizing up, the buffer is resized to exactly the requested
size. That is, if the current size is 1MiB, following requests
of 1MiB+1B and 1MiB+2B will both cause a resize.
It's preferable to limit the set of possible sizes so that every
reset doesn't tend to cause multiple resizes of almost the same size.
The natural set of sizes is powers of 2, because that's what the
underlying buddy allocator uses. No waste is caused by rounding up
the allocation to a power of 2.
4. The interval of 100'000 uses is both too low and too arbitrary.
This is up for discussion, but I think that it's preferable to base
the dynamics of the buffer on time, rather than the number of uses.
It's more predictable to humans.
The implementation proposed in this patch addresses these as follows:
1. Instead of resizing down to 0, we resize to the biggest size
seen in the last period.
As long as at least one maximal (up to a power of 2) "normal" request
appears each period, the buffer will never have to be resized.
2. The capacity of the buffer is always rounded up to the nearest
power of 2.
3. The resize down period is no longer measured in number of requests
but in real time.
Additionally, since a shared buffer in asynchronous code is quite a
footgun, some rudimentary refcounting is added to assert that only
one reference to the buffer exists at a time, and that the buffer isn't
downsized while a reference to it exists.
Fixes#13437
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
We are going to store sstable cells' values in fragmented_temporary_buffers.
This patch will allow checking these values with loggers.
Signed-off-by: Wojciech Mitros <wojciech.mitros@scylladb.com>
last fragment is unconditionally pushed to set of fragments, so if data
size is fragment-aligned, an empty fragment will be needlessly pushed to
the back of the fragment set.
note: i haven't tested if empty fragment at back of set will cause issues,
i think it won't, but this should be avoided anyway.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20210129231532.871405-3-raphaelsc@scylladb.com>
1) reuse default_fragment_size for knowledge of max fragment size
2) fragments_count is not a good name as it doesn't include last non-full
fragment (if present), so rename it.
3) simplify calculation of last fragment size
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20210129231532.871405-1-raphaelsc@scylladb.com>
Introduce `fragmented_temporary_buffer::allocate_to_fit` static
function returning an instance of the buffer of a specified size.
The allocated buffer fragments have a size of at most 128kb.
`bytes_ostream` has the same hard-coded limit, so just use the
same here.
This patch will be later needed for `raft::log_entry` raw data
serialization when writing to the underlying persistent storage.
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
When fragmented_temporary_buffer::view is created from a bytes_view,
_current is null. In that case, in remove_current(), null pointer offset
happens, and ubsan complains. Fix that.
This piece of logic was wrong for two unrelated reasons:
1. When fragmented_temporary_buffer::view is constructed from bytes_view,
_current is null. When remove_prefix was used on such view, null pointer
dereference happened.
2. It only worked for the first remove_prefix call. A second call would put a
wrong value in _current_position.
Offsetting a null pointer is undefined, and clang's ubsan complains.
Rearrange the arithmetic so we never offset a null pointer. A function
is introduced for the remaining contiguous bytes so it can cast the result
to size_t, avoiding a compare-of-different-signedness warning from gcc.
Closes#7373
Seastar recently lost support for the experimental Concepts Technical
Specification (TS) and gained support for C++20 concepts. Re-enable
concepts in Scylla by updating our use of concepts to the C++20
standard.
This change:
- peels off uses of the GCC6_CONCEPT macro
- removes inclusions of <seastar/gcc6-concepts.hh>
- replaces function-style concepts (no longer supported) with
equation-style concepts
- semicolons added and removed as needed
- deprecated std::is_pod replaced by recommended replacement
- updates return type constraints to use concepts instead of
type names (either std::same_as or std::convertible_to, with
std::same_as chosen when possible)
No attempt is made to improve the concepts; this is a specification
update only.
Message-Id: <20200531110254.2555854-1-avi@scylladb.com>
This patch adds fragmented_temporary_buffer_view::remove_suffix(). It is
also necessary to adjust remove_prefix() since now the total size of all
fragments may be larger than the size of the view if both those
operations are performed.
read_exactly(), when given a stream that does not contain the amount of data
requested, will loop endlessly, allocating more and more memory as it does, until
it fails with an exception (at which point it will release the memory).
Fix by returning an empty result, like input_stream::read_exactly() (which it
replaces). Add a test case that fails without a fix.
Affected callers are the native transport, commitlog replay, and internal
deserialization.
Fixes#4233.
Branches: master, branch-3.0
Tests: unit(dev)
Message-Id: <20190216150825.14841-1-avi@scylladb.com>
Replace stdx::optional and stdx::string_view with the C++ std
counterparts.
Some instances of boost::variant were also replaced with std::variant,
namely those that called seastar::visit.
Scylla now requires GCC 8 to compile.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190108111141.5369-1-duarte@scylladb.com>
The current implementation breaks the invariant that
_size_bytes = reduce(_fragments, &temporary_buffer::size)
In particular, this breaks algorithms that check the individual
segment size.
Correctly implement remove_suffix() by destroying superfluous
temporary_buffer's and by trimming the last one, if needed.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190103133523.34937-1-duarte@scylladb.com>
sprint() recently became more strict, throwing on sprint("%s", 5). Replace
with the more modern format().
Mechanically converted with https://github.com/avikivity/unsprint.
Seastar output_streams produce temporary_buffer<char>s.
fragmented_temporary_buffer represents a single fragmented buffer that
consists of, possibly multiple, temporary_buffer<char>s.
