The exponent of a big decimal string is parsed as an int32, adjusted for
the removed fractional part, and stored as an int32. When parsing values
like `1.23E-2147483647`, the unscaled value becomes `123`, and the scale
is adjusted to `2147483647 + 2 = 2147483649`. This exceeds the int32
limit, and since the scale is stored as an int32, it overflows and wraps
around, losing the value.
This patch fixes that the by parsing the exponent as an int64 value and
then adjusting it for the fractional part. The adjusted scale is then
checked to see if it is still within int32 limits before storing. An
exception is thrown if it is not within the int32 limits.
Note that strings with exponents that exceed the int32 range, like
`0.01E2147483650`, were previously not parseable as a big decimal. They
are now accepted if the final adjusted scale fits within int32 limits.
For the above value, unscaled_value = 1 and scale = -2147483648, so it
is now accepted. This is in line with how Java's `BigDecimal` parses
strings.
Fixes: #24581
Signed-off-by: Lakshmi Narayanan Sreethar <lakshmi.sreethar@scylladb.com>
Closesscylladb/scylladb#24640
Currently, the tri-compare operator for big_decimal (operator <=>), uses
a precise but potentially very expensive algorithm for comparing the
numbers: it first brings them to the same scale, then compares the
normalized unscaled values. big_decimal has abritrary precisions,
therefore the stored numbers can be arbitrarily large.
In extreme cases, comparing two numbers can result in huge amount of
memory allocated and stalls. If this type is used int he primary key of
a table, these comparisons can make the node completely unresponsive.
This patch adds the following fast-paths to operator <=>:
* An early return for the case of equal scales.
* An early return for different signs.
* An early return for the case where one or both of the numbers are 0.
* A fast algorithm for detecting the case where the there is a big
difference between the two numbers. This algorithm works only with the
scales and is able to compare the two numbers by using only one division
and some additions and substractions. This algorithm is imprecise and
when the numbers are closer than its confidence window, it will
fall-back to the current slow but precise tri-compare.
All but the last case should have been fast before as well, but the
scale-compare algorithm makes a huge difference. Numbers, which would
previously make the node unresponsive, now compare in constant-time.
Fixes: scylladb/scylladb#21716Closesscylladb/scylladb#21715
Our "sstring_view" is an historic alias for the standard std::string_view.
The patch changes the last remaining random uses of this old alias across
our source directory to the standard type name.
After this patch, there are no more uses of the "sstring_view" alias.
It will be removed in the following patch.
Refs #4062.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
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
before this change, we rely on `using namespace seastar` to use
`seastar::format()` without qualifying the `format()` with its
namespace. this works fine until we changed the parameter type
of format string `seastar::format()` from `const char*` to
`fmt::format_string<...>`. this change practically invited
`seastar::format()` to the club of `std::format()` and `fmt::format()`,
where all members accept a templated parameter as its `fmt`
parameter. and `seastar::format()` is not the best candidate anymore.
despite that argument-dependent lookup (ADT for short) favors the
function which is in the same namespace as its parameter, but
`using namespace` makes `seastar::format()` more competitive,
so both `std::format()` and `seastar::format()` are considered
as the condidates.
that is what is happening scylladb in quite a few caller sites of
`format()`, hence ADT is not able to tell which function the winner
in the name lookup:
```
/__w/scylladb/scylladb/mutation/mutation_fragment_stream_validator.cc:265:12: error: call to 'format' is ambiguous
265 | return format("{} ({}.{} {})", _name_view, s.ks_name(), s.cf_name(), s.id());
| ^~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/14/../../../../include/c++/14/format:4290:5: note: candidate function [with _Args = <const std::basic_string_view<char> &, const seastar::basic_sstring<char, unsigned int, 15> &, const seastar::basic_sstring<char, unsigned int, 15> &, const utils::tagged_uuid<table_id_tag> &>]
4290 | format(format_string<_Args...> __fmt, _Args&&... __args)
| ^
/__w/scylladb/scylladb/seastar/include/seastar/core/print.hh:143:1: note: candidate function [with A = <const std::basic_string_view<char> &, const seastar::basic_sstring<char, unsigned int, 15> &, const seastar::basic_sstring<char, unsigned int, 15> &, const utils::tagged_uuid<table_id_tag> &>]
143 | format(fmt::format_string<A...> fmt, A&&... a) {
| ^
```
in this change, we
change all `format()` to either `fmt::format()` or `seastar::format()`
with following rules:
- if the caller expects an `sstring` or `std::string_view`, change to
`seastar::format()`
- if the caller expects an `std::string`, change to `fmt::format()`.
because, `sstring::operator std::basic_string` would incur a deep
copy.
we will need another change to enable scylladb to compile with the
latest seastar. namely, to pass the format string as a templated
parameter down to helper functions which format their parameters.
to miminize the scope of this change, let's include that change when
bumping up the seastar submodule. as that change will depend on
the seastar change.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
assert() is traditionally disabled in release builds, but not in
scylladb. This hasn't caused problems so far, but the latest abseil
release includes a commit [1] that causes a 1000 insn/op regression when
NDEBUG is not defined.
Clearly, we must move towards a build system where NDEBUG is defined in
release builds. But we can't just define it blindly without vetting
all the assert() calls, as some were written with the expectation that
they are enabled in release mode.
To solve the conundrum, change all assert() calls to a new SCYLLA_ASSERT()
macro in utils/assert.hh. This macro is always defined and is not conditional
on NDEBUG, so we can later (after vetting Seastar) enable NDEBUG in release
mode.
[1] 66ef711d68Closesscylladb/scylladb#20006
since #13452, we switched most of the caller sites from std::regex
to boost::regex. in this change, all occurences of `#include <regex>`
are dropped unless std::regex is used in the same source file.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13765
now that we are using C++20, it'd be more convenient if we can use
the <=> operator for comparing. the compiler creates the 6 other
operators for us if the <=> operator is defined. so the code is more
compacted.
in this change, `big_decimal::compare()` is replaced with `operator<=>`,
and its caller is updated accordingly.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
before this change in the worst case, the underlying
`number::compare()` gets called twice. as it is used by Boost::multiprecision
to implement the comparing operators of `number`. but since we can
have the result in one go, there is no need to to perform the
comparison multiple times.
so, in this change, we just call `number::compare()` explicitly,
and use it to implement `compare()`. this should save a call of
`number::compare()`. also, the chained ternary expression is
replaced using if-else statement for better readability.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
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
Clang has some difficulty with the boost::cpp_int constructor from string_view.
In fact it is a mess of enable_if<>s so a human would have trouble too.
Work around it by converting to std::string. This is bad for performance, but
this constructor is not going to be fast in any case.
Hopefully a fix will arrive in clang or boost.
Closes#7389
A negative scale was being passed an a positive value to
boost::multiprecision::pow, which would never finish.
Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
Big decimals are, among other use cases, used as a main number
type for alternator, and as such can appear on the fast path.
Parsing big decimals was performed via std::regex, which is not
precisely famous for its speeds, and also enforces unnecessary
string copying. Therefore, the implementation is replaced
with an open-coded version based on string_views.
One previous iteration of this series also included
a hand-coded state machine implementation, but it proved
to be slower than the slightly naive string_view one.
Overall, execution time is reduced by 61.6% according to
microbenchmarks, which sounds like a promising improvement.
Perf results:
test iterations median mad min max
Regex (original):
big_decimal_test.from_string 88895 11.228us 25.891ns 11.202us 11.510us
String view (new):
big_decimal_test.from_string 232334 4.303us 21.660ns 4.282us 4.736us
State machine (experimental, ditched):
big_decimal_test.from_string 148318 6.723us 51.896ns 6.672us 6.877us
Tests: unit(dev + release(big_decimal_test))
The goal is to forward-declare utils::multiprecision_int, something
beyond my capabilities for boost::multiprecision::cpp_int, to reduce
compile time bloat.
The patch is mostly search-and-replace, with a few casts added to
disambiguate conversions the compiler had trouble with.
Different versions of boost have different rules for what conversions
from cpp_int to smaller intergers are allowed.
We already had a function that worked with all supported versions, but
it was not being use by lua.
Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
Message-Id: <20200104041028.215153-1-espindola@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>
* seastar d59fcef...b924495 (2):
> build: Fix protobuf generation rules
> Merge "Restructure files" from Jesse
Includes fixup patch from Jesse:
"
Update Seastar `#include`s to reflect restructure
All Seastar header files are now prefixed with "seastar" and the
configure script reflects the new locations of files.
Signed-off-by: Jesse Haber-Kucharsky <jhaberku@scylladb.com>
Message-Id: <5d22d964a7735696fb6bb7606ed88f35dde31413.1542731639.git.jhaberku@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.
