- raft_sys_table_storage::store_snapshot_descriptor now receives a number of
preserved items in the log, rather than _config.snapshot_trailing value;
- Incorrect check for truncated number of items in store_snapshot_descriptor
was removed.
Fixesscylladb/scylladb#16817Fixesscylladb/scylladb#20080
With implicit conversion of tagged integers to untagged ones going away,
explicitly tag (or untag, as necessary) the operands of the following
operations, in raft/log.{cc,h}:
- addition of tagged and untagged (both should be tagged)
- comparison (relop) between tagged an untagged (both should be tagged)
- subscripting an array, or offsetting an iterator, by tagged (should be
untagged)
- comparing an array bound against tagged (should be untagged)
- subtracting tagged from an array bound (should be untagged)
Note: these files mix uniform initialization syntax (index_t{...}) with
constructor call syntax (index_t()), with the former being more frequent.
Stick with the former here too, for consistency.
Signed-off-by: Laszlo Ersek <laszlo.ersek@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
in in {fmt} before v10, it provides the specialization of `fmt::formatter<..>`
for `std::string_view` as well as the specialization of `fmt::formatter<..>`
for `fmt::string_view` which is an implementation builtin in {fmt} for
compatibility of pre-C++17. and this type is used even if the code is
compiled with C++ stadandard greater or equal to C++17. also, before v10,
the `fmt::formatter<std::string_view>::format()` is defined so it accepts
`std::string_view`. after v10, `fmt::formatter<std::string_view>` still
exists, but it is now defined using `format_as()` machinery, so it's
`format()` method does not actually accept `std::string_view`, it
accepts `fmt::string_view`, as the former can be converted to
`fmt::string_view`.
this is why we can inherit from `fmt::formatter<std::string_view>` and
use `formatter<std::string_view>::format(foo, ctx);` to implement the
`format()` method with {fmt} v9, but we cannot do this with {fmt} v10,
and we would have following compilation failure:
```
FAILED: service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o
/home/kefu/.local/bin/clang++ -DFMT_DEPRECATED_OSTREAM -DFMT_SHARED -DSCYLLA_BUILD_MODE=release -DSEASTAR_API_LEVEL=7 -DSEASTAR_LOGGER_COMPILE_TIME_FMT -DSEASTAR_LOGGER_TYPE_STDOUT -DSEASTAR_SCHEDULING_GROUPS_COUNT=16 -DSEASTAR_SSTRING -DXXH_PRIVATE_API -DCMAKE_INTDIR=\"RelWithDebInfo\" -I/home/kefu/dev/scylladb -I/home/kefu/dev/scylladb/build/gen -I/home/kefu/dev/scylladb/seastar/include -I/home/kefu/dev/scylladb/build/seastar/gen/include -I/home/kefu/dev/scylladb/build/seastar/gen/src -ffunction-sections -fdata-sections -O3 -g -gz -std=gnu++20 -fvisibility=hidden -Wall -Werror -Wextra -Wno-error=deprecated-declarations -Wimplicit-fallthrough -Wno-c++11-narrowing -Wno-deprecated-copy -Wno-mismatched-tags -Wno-missing-field-initializers -Wno-overloaded-virtual -Wno-unsupported-friend -Wno-enum-constexpr-conversion -Wno-unused-parameter -ffile-prefix-map=/home/kefu/dev/scylladb=. -march=westmere -mllvm -inline-threshold=2500 -fno-slp-vectorize -U_FORTIFY_SOURCE -Werror=unused-result -MD -MT service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o -MF service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o.d -o service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o -c /home/kefu/dev/scylladb/service/topology_state_machine.cc
/home/kefu/dev/scylladb/service/topology_state_machine.cc:254:41: error: no matching member function for call to 'format'
254 | return formatter<std::string_view>::format(it->second, ctx);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
/usr/include/fmt/core.h:2759:22: note: candidate function template not viable: no known conversion from 'seastar::basic_sstring<char, unsigned int, 15>' to 'const fmt::basic_string_view<char>' for 1st argument
2759 | FMT_CONSTEXPR auto format(const T& val, FormatContext& ctx) const
| ^ ~~~~~~~~~~~~
```
because the inherited `format()` method actually comes from
`fmt::formatter<fmt::string_view>`. to reduce the confusion, in this
change, we just inherit from `fmt::format<string_view>`, where
`string_view` is actually `fmt::string_view`. this follows
the document at
https://fmt.dev/latest/api.html#formatting-user-defined-types,
and since there is less indirection under the hood -- we do not
use the specialization created by `FMT_FORMAT_AS` which inherit
from `formatter<fmt::string_view>`, hopefully this can improve
the compilation speed a little bit. also, this change addresses
the build failure with {fmt} v10.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18299
before this change, we rely on the default-generated fmt::formatter
created from operator<<, but fmt v10 dropped the default-generated
formatter.
in this change, we define formatters for `raft::log`, and drop its
operator<<.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17301
Before this patch we could get an OOM if we
received several big commands. The number of
commands was small, but their total size
in bytes was large.
snapshot_trailing_size is needed to guarantee
progress. Without this limit the fsm could
get stuck if the size of the next item is
greater than max_log_size - (size of trailing entries).
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
There are situations where a node outside the current configuration is
the only node that can become a leader. We become candidates in such
cases. But there is an easy check for when we don't need to; a comment was
added explaining that.
We add a function `log_last_conf_before(index_t)` to `fsm` which, given
an index greater than the last snapshot index, returns the configuration
at this index, i.e. the configuration of the last configuration entry
before this index.
This function is then used in `applier_fiber` to obtain the correct
configuration to be stored in a snapshot.
In order to ensure that the configuration can be obtained, i.e. the
index we're looking at is not smaller than the last snapshot index, we
strengthen the conditions required for taking a snapshot: we check that
`_fsm` has not yet applied a snapshot at a larger index (which it may
have due to a remote snapshot install request). This also causes fewer
unnecessary snapshots to be taken in general.
The old name was incorrect, in case apply_snapshot() was called with
non-zero trailing entries, the total log length is greater than the
length of the part that is not stored in a snapshot.
Fix spelling in related comments.
Rename fsm::wait() to fsm::wait_max_log_size(), it's a more
specific name. Rename max_log_length to max_log_size to use
'size' rather than 'length' consistently for log size.
Replace it with a private _first_idx, which is maintained
along with the rest of class log state.
_first_idx is a name consistent with counterpart last_idx().
Do not use a function since going forward we may want
to remove Raft index from struct log_entry, so should rely
less on it.
This fixes a bug when _last_conf_idx was not reset
after apply_snapshot() because start_idx() was pointing
to a non-existent entry.
If the log is empty, we must use snapshot's term,
since the log could be right after taking a snapshot
when no trailing entries were kept.
This fixes a rare possible bug when a log matching
rule could be violated during elections by a follower
with a log which was just truncated after a snapshot.
A separate unit test for the issue will follow.
raft::log::start_idx() is currently not meaningful
in case the log is empty.
Avoid using it in fsm::replicate_to() and avoid manual search for
previous log term, instead encapsulate the search in log::term_for().
As a side effect we currently return a correct term (0)
when log matching rule is exercised for an empty log
and the very first snapshot with term 0. Update raft_etcd_test.cc
accordingly.
This change happens to reduce the overall line count.
While at it, improve the comments in raft::replicate_to().
When initializing the log, find the most recent configuration
change index, if present.
Maintain the most recent configuration change index when
the log is truncated or entries are appended to it.
The last configuration change index will be used by FSM when it enters
candidate or leader state to fetch the current configuration.
We never truncate beyond a single in-progress configuration
change, so storing the previous value of last_conf_idx
helps avoid log backward scan on truncation in 100% of cases.
Remove all unused log constructors.
Combine structs for append request send and receive into a single
struct.
Author: Gleb Natapov <gleb@scylladb.com>
Date: Mon Nov 23 14:33:14 2020 +0200
To prevent the log to take too much memory introduce a mechanism that
limits the log to a certain size. If the size is reached no new log
entries can be submitted until previous entries are committed and
snapshotted.
This patch allows to leave snapshot_trailing amount of entries
when a state machine is snapshotted and raft log entries are dropped.
Those entries can be used to catch up nodes that are slow without
requiring snapshot transfer. The value is part of the configuration
and can be changed.
This patch introduces partial RAFT implementation. It has only log
replication and leader election support. Snapshotting and configuration
change along with other, smaller features are not yet implemented.
The approach taken by this implementation is to have a deterministic
state machine coded in raft::fsm. What makes the FSM deterministic is
that it does not do any IO by itself. It only takes an input (which may
be a networking message, time tick or new append message), changes its
state and produce an output. The output contains the state that has
to be persisted, messages that need to be sent and entries that may
be applied (in that order). The input and output of the FSM is handled
by raft::server class. It uses raft::rpc interface to send and receive
messages and raft::storage interface to implement persistence.
