Before the patch, dht::sharder could be instantiated and it would
behave like a static sharder. This is not safe with regards to
extensions of the API because if a derived implementation forgets to
override some method, it would incorrectly default to the
implementation from static sharder. Better to fail the compilation in
this case, so extract static sharder logic to dht::static_sharder
class and make all methods in dht::sharder pure virtual.
This also allows us to have algorithms indicate that they only work
with static sharder by accepting the type, and have compile-time
safety for this requirement.
schema::get_sharder() is changed to return the static_sharder&.
`system_keyspace::read_cdc_generation_opt` queries
`system.cdc_generations_v3`, which stores ids of CDC generations
as timeuuids. This function shouldn't be called with a normal uuid
(used by `system.cdc_generations_v2` to store generation ids).
Such a call would end with a marshaling error.
Before this patch,`retrieve_generation_data_v2` could call
`system_keyspace::read_cdc_generation_opt` with a normal uuid if
the generation wasn't present in `system.cdc_generations_v2`.
This logic caused a marshaling error while handling the
`check_and_repair_cdc_streams` request in the
`cdc_test.TestCdc.test_check_and_repair_cdc_streams_liveness` dtest.
This patch fixes the code being added in 6.0, no need to backport it.
Fixesscylladb/scylladb#18473Closesscylladb/scylladb#18483
because of https://bugzilla.redhat.com/show_bug.cgi?id=2278689,
the rebuilt abseil package provided by fedora has different settings
than the ones if the tree is built with the sanitizer enabled. this
inconsistency leads to a crash.
to address this problem, we have to reinstate the abseil submodule, so
we can built it with the same compiler options with which we build the
tree.
in this change
* Revert "build: drop abseil submodule, replace with distribution abseil"
* update CMake building system with abseil header include settings
* bump up the abseil submodule to the latest LTS branch of abseil:
lts_2024_01_16
* update scylla-gdb.py to adapt to the new structure of
flat_hash_map
This reverts commit 8635d24424.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18511
We make the `consistent-topology-changes` experimental feature
unused and assumed to be true in 6.0. We remove code branches that
executed if `consistent-topology-changes` was disabled.
since we do not rely on FMT_DEPRECATED_OSTREAM to define the
fmt::formatter for us anymore, let's stop defining `FMT_DEPRECATED_OSTREAM`.
in this change,
* utils: drop the range formatters in to_string.hh and to_string.c, as
we don't use them anymore. and the tests for them in
test/boost/string_format_test.cc are removed accordingly.
* utils: use fmt to print chunk_vector and small_vector. as
we are not able to print the elements using operator<< anymore
after switching to {fmt} formatters.
* test/boost: specialize fmt::details::is_std_string_like<bytes>
due to a bug in {fmt} v9, {fmt} fails to format a range whose
element type is `basic_sstring<uint8_t>`, as it considers it
as a string-like type, but `basic_sstring<uint8_t>`'s char type
is signed char, not char. this issue does not exist in {fmt} v10,
so, in this change, we add a workaround to explicitly specialize
the type trait to assure that {fmt} format this type using its
`fmt::formatter` specialization instead of trying to format it
as a string. also, {fmt}'s generic ranges formatter calls the
pair formatter's `set_brackets()` and `set_separator()` methods
when printing the range, but operator<< based formatter does not
provide these method, we have to include this change in the change
switching to {fmt}, otherwise the change specializing
`fmt::details::is_std_string_like<bytes>` won't compile.
* test/boost: in tests, we use `BOOST_REQUIRE_EQUAL()` and its friends
for comparing values. but without the operator<< based formatters,
Boost.Test would not be able to print them. after removing
the homebrew formatters, we need to use the generic
`boost_test_print_type()` helper to do this job. so we are
including `test_utils.hh` in tests so that we can print
the formattable types.
* treewide: add "#include "utils/to_string.hh" where
`fmt::formatter<optional<>>` is used.
* configure.py: do not define FMT_DEPRECATED_OSTREAM
* cmake: do not define FMT_DEPRECATED_OSTREAM
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
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, `fmt::formatter` is added for following types for backward compatibility with {fmt} < 10:
* `utils::bad_exception_container_access`
* `cdc::no_generation_data_exception`
* classes derived from `sstables::malformed_sstable_exception`
* classes derived from `cassandra_exception`
Refs https://github.com/scylladb/scylladb/issues/13245Closesscylladb/scylladb#17944
* github.com:scylladb/scylladb:
cdc: add fmt::formatter for exception types in data_dictionary.hh
utils: add fmt::formatter for utils::bad_exception_container_access
sstables: add fmt::formatter for classes derived from sstables::malformed_sstable_exception
exceptions: add fmt::formatter for classes derived from cassandra_exception
cdc: add fmt::formatter for cdc::no_generation_data_exception
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, `fmt::formatter<cdc::no_generation_data_exception>` is
added for backward compatibility with {fmt} < 10.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
There is no need to map this node's inet_address to host_id.
The storage_service can easily just pass the local host_id.
While at it, get the other node's host_id directly
from their endpoint_state instead of looking it up
yet again in the gossiper, using the nodes' address.
Refs #12283
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
in af2553e8, we added formatters for cdc::image_mode and
cdc::delta_mode. but in that change, we failed to qualify `string_view`
with `std::` prefix. even it compiles, it depends on a `using
std::string_view` or a more error-prone `using namespace std`.
neither of which shold be relied on. so, in this change, we
add the `std::` prefix to `string_view`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17459
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
cdc::image_mode and cdc::delta_mode, and drop their operator<<:s.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17381
Before this patch, writes to the previous CDC generations would
always be rejected. After this patch, they will be accepted if
the write's timestamp is greater than `now - generation_leeway`.
This change was proposed around 3 years ago. The motivation was
to improve user experience. If a client generates timestamps by
itself and its clock is desynchronized with the clock of the node
the client is connected to, there could be a period during
generation switching when writes fail. We didn't consider this
problem critical because the client could simply retry a failed
write with a higher timestamp. Eventually, it would succeed. This
approach is safe because these failed writes cannot have any side
effects. However, it can be inconvenient. Writing to previous
generations was proposed to improve it.
The idea was rejected 3 years ago. Recently, it turned out that
there is a case when the client cannot retry a write with the
increased timestamp. It happens when a table uses CDC and LWT,
which makes timestamps permanent. Once Paxos commits an entry with
a given timestamp, Scylla will keep trying to apply that entry
until it succeeds, with the same timestamp. Applying the entry
involves writing to the CDC log table. If it fails, we get stuck.
It's a major bug with an unknown perfect solution.
Allowing writes to previous generations for `generation_leeway` is
a probabilistic fix that should solve the problem in practice.
Note that allowing writes only to the previous generation might
not be enough. With the Raft-based topology, it is possible to
add multiple nodes concurrently. Moreover, tablets make streaming
instant, which allows the topology coordinator to add multiple nodes
very quickly. So, creating generations with almost identical
timestamps is possible. Then, we could encounter the same bug but,
for example, for a generation before the previous generation.
When a node enters recovery after being in raft topology mode, topology
operations switch back to legacy mode. We want CDC to keep working when
that happens, so we need for the legacy code to be able to access
generations created back in raft mode - so that the node can still
properly serve writes to CDC log tables.
In order to make this possible, modify the legacy logic to also look for
a cdc generation in raft tables, if it is not found in legacy tables.
In raft topology mode CDC information is propagated through group 0.
Prevent the generation service from reacting to gossiper notifications
after we made the switch to raft mode.
Rather than calling on_change for each particular
application_state, pass an endpoint_state::map_type
with all changed states, to be processed as a batch.
In particular, thise allows storage_service::on_change
to update_peer_info once for all changed states.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
None of the subscribers is doing anything before_change.
This is done before changing `on_change` in the following patch.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Now all the callers have it at hands (spoiler: not yet initialized, but
still) so the params can also have it.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Previous patch added params to r.s. classes' constructors, but callers
don't construct those directly, instead they use the create_r.s.()
wrapper. This patch adds params to the wrapper too.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
We do not yet support enabling CDC in a keyspace that uses tablets
(Refs #16317). But the problem is that today, if this is attempted,
we get a nasty failure: the CDC code creates the extra CDC log table,
it doesn't get tablets, and Raft gets surprised and croaks with a
message like:
Raft instance is stopped, reason: "background error,
std::_Nested_exceptionraft::state_machine_error (State machine error at
raft/server.cc:1230): std::runtime_error (Tablet map not found for
table 48ca1620-9ea5-11ee-bd7c-22730ed96b85)
After Raft croaks, Scylla never recovers until it is rebooted.
In this patch, we replace this disaster by a graceful error - a CREATE
TABLE or ALTER TABLE operation with CDC enabled will fail in a clear way,
and allowing Scylla to continue operating normally after this failed request.
This fix is important for allowing us to run tests on Scylla with
tablets, and although CDC tests will fail as expected, they won't
fail the other tests that follow (Refs #16473).
Fixes#16318
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#16474
Change the token_metadata type to token_metadata2 in
the signatures of CDC-related methods in
storage_service and cdc/generation. Use
get_new_strong to get a pointer to the new host_id-based
token_metadata from the inet_address-based one,
living in the shared_token_metadata.
The starting point of the patch is in
storage_service::handle_global_request. We change the
tmptr type to token_metadata2 and propagate the change
down the call chains. This includes token-related methods
of the boot_strapper class.
NodeId is used in all internal token_metadata data structures, that
previously used inet_address. We choose topology::key_kind based
on the value of the template parameter.
generic_token_metadata::update_topology overload with host_id
parameter is added to make update_topology_change_info work,
it now uses NodeId as a parameter type.
topology::remove_endpoint(host_id) is added to make
generic_token_metadata::remove_endpoint(NodeId) work.
pending_endpoints_for and endpoints_for_reading are just removed - they
are not used and not implemented. The declarations were left by mistake
from a refactoring in which these methods were moved to erm.
generic_token_metadata_base is extracted to contain declarations, common
to both token_metadata versions.
Templates are explicitly instantiated inside token_metadata.cc, since
implementation part is also a template and it's not exposed to the header.
There are no other behavioral changes in this commit, just syntax
fixes to make token_metadata a template.
Returns this node's endpoint_state_ptr.
With this entry point, the caller doesn't need to
get_broadcast_address.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Fixes some typos as found by codespell run on the code.
In this commit, I was hoping to fix only comments, not user-visible alerts, output, etc.
Follow-up commits will take care of them.
Refs: https://github.com/scylladb/scylladb/issues/16255
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
to have feature parity with `configure.py`. we won't need this
once we migrate to C++20 modules. but before that day comes, we
need to stick with C++ headers.
we generate a rule for each .hh files to create a corresponding
.cc and then compile it, in order to verify the self-containness of
that header. so the number of rule is quite large, to avoid the
unnecessary overhead. the check-header target is enabled only if
`Scylla_CHECK_HEADERS` option is enabled.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#15913
After adding the new prepare_new_column_family_announcement that
doesn't assume the existence of a keyspace, we also need to get
rid of the same assumption in all on_before_create_column_family
calls. After all, they may be initiated before creating the
keyspace. However, some listeners require keyspace_metadata, so we
pass it as a new parameter.
This reverts commit 4b80130b0b, reversing
changes made to a5519c7c1f. It's suspected
of causing dtest failures due to a bug in coroutine::parallel_for_each.
After adding the new prepare_new_column_family_announcement that
doesn't assume the existence of a keyspace, we also need to get
rid of the same assumption in all on_before_create_column_family
calls. After all, they may be initiated before creating the
keyspace. However, some listeners require keyspace_metadata, so we
pass it as a new parameter.
We change the type of IDs in CDC_GENERATIONS_V3 to timeuuid to
give them a time-based order. We also change how we initialize
them so that the new CDC generation always has the highest ID.
This is the last step to enabling the efficient clearing of
obsolete CDC generation data.
Additionally, we change the types of current_cdc_generation_uuid,
new_cdc_generation_data_uuid and the second values of the elements
in unpublished_cdc_generations to timeuuid, so that they match id
in CDC_GENERATIONS_V3.
After moving the creation of uuid out of
make_new_generation_description, this function only calls the
topology_description_generator's constructor and its generate
method. We could remove this function, but we instead simplify
the code by removing the topology_description_generator class.
We can do this refactor because make_new_generation_description
is the only place using it. We inline its generate method into
make_new_generation_description and turn its private methods into
static functions.
In the future commit, we change how we initialize uuid of the
new CDC generation in the Raft-based topology. It forces us to
move this initialization out of the make_new_generation_data
function shared between Raft-based and gossiper-based topologies.
We also rename make_new_generation_data to
make_new_generation_description since it only returns
cdc::topology_description now.
We make CDC_GENERATIONS_V3 single-partition by adding the key
column and changing the clustering key from range_end to
(id, range_end). This is the first step to enabling the efficient
clearing of obsolete CDC generation data, which we need to prevent
Raft-topology snapshots from endlessly growing as we introduce new
generations over time. The next step is to change the type of the id
column to timeuuid. We do it in the following commits.
After making CDC_GENERATIONS_V3 single-partition, there is no easy
way of preserving the num_ranges column. As it is used only for
sanity checking, we remove it to simplify the implementation.
In the following commit, we implement the
get_cdc_generation_mutations_v3 function very similar to
get_cdc_generation_mutations_v2. The only differences in creating
mutations between CDC_GENERATIONS_V2 and CDC_GENERATIONS_V3 are:
- a need to set the num_ranges cell for CDC_GENERATIONS_V2,
- different partition keys,
- different clustering keys.
To avoid code duplication, we introduce
get_common_cdc_generation_mutations, which does most of the work
shared by both functions.
In the following commits, we modify the CDC_GENERATIONS_V3 schema
to enable efficient clearing of obsolete CDC generation data.
These modifications make the current get_cdc_generation_mutations
work only for the CDC_GENERATIONS_V2 schema, and we need a new
function for CDC_GENERATIONS_V3, so we add the "_v2" suffix.
Now that the endpoint_state isn't change in place
we do not need to copy it to each subscriber.
We can rather just pass the lw_shared_ptr holding
a snapshot of it.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
No need to lookup the application_state again using the
endpoint, as both callers already have a reference to
the endpoint_state handy.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Before changing _endpoint_state_map to hold a
lw_shared_ptr<endpoint_state>, provide synchronous helpers
for users to traverse all endpoint_states with no need
to copy them (as long as the called func does not yield).
With that, gossiper::get_endpoint_states() can be made private.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
As was described in the previous patch, this method is explicitly called
by storage service after updating the bootstrap state, so it's unneeded
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The legacy_handle_cdc_generation() checks if the node had bootstrapped
with the help of system_keyspace method. The former is called in two
cases -- on boot via cdc_generation_service::after_join() and via
gossiper on_...() notifications. The notifications, in turn, are set up
in the very same after_join().
The after_join(), in turn, is called from storage_service explicitly
after the bootstrap state is updated to be "complete", so the check for
the state in legacy_handle_...() seems unnecessary. However, there's
still the case when it may be stepped on -- decommission. When performed
it calls storage_service::leave_ring() which udpates the bootstrap state
to be "needed", thus preventing the cdc gen. service from doing anything
inside gossiper's on_...() notifications.
It's more correct to stop cdc gen. service handling gossiper
notifications by unsubscribing it, but by adding fragile implicit
dependencies on the bootstrap state.
Checks for sys.dist.ks in the legacy_handle_...() are kept in a form
of on-internal-error. The system distributed keyspace is activated by
storage service even before the bootstrap state is updated and is
never deactivated, but it's anyway good to have this assertion.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
This series cleans up and hardens the endpoint locking design and
implementation in the gossiper and endpoint-state subscribers.
We make sure that all notifications (expect for `before_change`, that
apparently can be dropped) are called under lock_endpoint, as well as
all calls to gossiper::replicate, to serialize endpoint_state changes
across all shards.
An endpoint lock gets a unique permit_id that is passed to the
notifications and passed back by them if the notification functions call
the gossiper back for the same endpoint on paths that modify the
endpoint_state and may acquire the same endpoint lock - to prevent a
deadlock.
Fixes scylladb/scylladb#14838
Refs scylladb/scylladb#14471
Closes#14845
* github.com:scylladb/scylladb:
gossiper: replicate: ensure non-null permit
gossiper: add_saved_endpoint: lock_endpoint
gossiper: mark_as_shutdown: lock_endpoint
gossiper: real_mark_alive: lock_endpoint
gossiper: advertise_token_removed: lock_endpoint
gossiper: do_status_check: lock_endpoint
gossiper: remove_endpoint: lock_endpoint if needed
gossiper: force_remove_endpoint: lock_endpoint if needed
storage_service: lock_endpoint when removing node
gossiper: use permit_id to serialize state changes while preventing deadlocks
gossiper: lock_endpoint: add debug messages
utils: UUID: make default tagged_uuid ctor constexpr
gossiper: lock_endpoint must be called on shard 0
gossiper: replicate: simplify interface
gossiper: mark_as_shutdown: make private
gossiper: convict: make private
gossiper: mark_as_shutdown: do not call convict
Pass permit_id to subscribers when we acquire one
via lock_endpoint. The subscribers then pass it back to
gossiper for paths that acquire lock_endpoint for
the same endpoint, to detect nested locks when the endpoint
is locked with the same permit_id.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
We add the CDC generation optimality check in
`storage_service::raft_check_and_repair_cdc_streams` so that it doesn't
create new generations when unnecessary. Since
`generation_service::check_and_repair_cdc_streams` already has this
check, we extract it to the new `is_cdc_generation_optimal` function to
not duplicate the code.
After this change, multiple tasks could wait for a single generation
change. Calling `signal` on `topology_state_machine.event` would't wake
them all. Moreover, we must ensure the topology coordinator wakes when
his logic expects it. Therefore, we change all `signal` calls on
`topology_state_machine.event` to `broadcast`.
We delay the deletion of the `new_cdc_generation` request to the moment
when the topology transition reaches the `publish_cdc_generation` state.
We need this change to ensure the added CDC generation optimality check
in the next commit has an intended effect. If we didn't make it, it
would be possible that a task makes the `new_cdc_generation` request,
and then, after this request was removed but before committing the new
generation, another task also makes the `new_cdc_generation` request. In
such a scenario, two generations are created, but only one should. After
delaying the deletion of `new_cdc_generation` requests, the second
request would have no effect.
Additionally, we modify the `test_topology_ops.py` test in a way that
verifies the new changes. We call
`storage_service::raft_check_and_repair_cdc_streams` multiple times
concurrently and verify that exactly one generation has been created.
Fixes#14055Closes#14789
* github.com:scylladb/scylladb:
storage_service: raft_check_and_repair_cdc_streams: don't create a new generation if current one is optimal
storage_service: delay deletion of the new_cdc_generation request
raft topology: broadcast on topology_state_machine.event instead of signal
cdc: implement the is_cdc_generation_optimal function
In the following commits, we add the CDC generation optimality
check to storage_service::raft_check_and_repair_cdc_streams so
that it doesn't create new CDC generations when unnecessary. Since
generation_service::check_and_repair_cdc_streams already has
this check, we extract it to the new is_cdc_generation_optimal
function to not duplicate the code.
As a preparation for ensuring access safety for column families
related maps, add tables_metadata, access to members of which
would be protected by rwlock.
