to_repair_rows_on_wire() moves the contents of its input std::list
and is careful to yield after each element, but the final destruction
of the input list still deals with all of the list elements without
yielding. This is expensive as not all contents of repair_row are moved
(_dk_with_hash is of type lw_shared_ptr<const decorated_key_with_hash>).
To fix, destroy each row element as we move along. This is safe as we
own the input and don't reference row_list other than for the iteration.
Fixes#24725.
Closesscylladb/scylladb#24726
Move 3rd party services starting under `try` clause to avoid situation that main process is collapses without going stopping services.
Without this, if something wrong during start it will not trigger execution exit artifacts, so the process will stay forever.
This functionality in 2025.2 and can potentially affect jobs, so backport needed.
Closesscylladb/scylladb#24734
* github.com:scylladb/scylladb:
test.py: use unique hostname for Minio
test.py: Catch possible exceptions during 3rd party services start
This commit migrates the Software Bill Of Materials (SBOM) page
added to the Enterprise docs with https://github.com/scylladb/scylla-enterprise/pull/5067.
The only difference is the link to the SBOM files - it was Enterprise SBOM in the Enterprise docs,
while here is a link to the ScyllaDB SBOM.
It's a follow-up of migration to Source Avalable and should be backported
to all Source Available versions - 2025.1 and later.
Fixes https://github.com/scylladb/scylladb/issues/24730Closesscylladb/scylladb#24735
With this change if something will go wrong during starting services,
they are still will be shuted down on the finally clause. Without it can
hang forever
This patch adds tests reproducing issue #24581, where Scylla incorrectly
parsed "decimal"-type literals in CQL with very high exponents, near or
above the 32-bit limit.
For example, 1.1234e-2147483647 was incorrectly read as 1.1234E+2147483649,
while it should be (as we explain in comments in the test) an error.
The tests in this patch failed (in multiple checks) before #24581 was
fixed, and pass after it was fixed.
These tests all pass on Cassandra 3, confirming our understanding on the
limits of "decimal" to be correct. But they fail on Cassandra 4 and 5 due
to a regression https://issues.apache.org/jira/browse/CASSANDRA-20723
in Cassandra, that mistakenly limited "decimal" exponents to just 309.
Refs #24581
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#24646
This commit removes the Non-Reserved CQL Keywords and Reserved CQL Keywords pages-keyword
as that content is already covered on the Appendices page.
Redirections are added to avoid 404s for the removed pages.
In addition, the Appendices page title is extended with "Reserved CQL Keywords and Types"
to help users understand what those appendices are about.
Fixes https://github.com/scylladb/scylladb/issues/24319Closesscylladb/scylladb#24320
Currently the test indiscriminately injects failures into the flushes of
any table, via the IO extension mechanism. The tests want to check that
the node correctly handles the IO error by self isolating, however the
indiscriminate IO errors can have unintended consequences when they hit
raft, leading to disorderly shutdown and failure of the tests. Testing
raft's resiliency to IO errors if of course worth doing, but it is not
the goal of this particular test, so to avoid the fallout, the IO errors
are limited to the test tables only.
Fixes: https://github.com/scylladb/scylladb/issues/24637Closesscylladb/scylladb#24638
We use patchelf to rewrite the dynamic loader (known as the interpreter)
of the binaries we ship, so we can point to our shipped dynamic loader,
which is compatible with our binaries, rather than rely on the distribution's
dynamic loader, which is likely to be incompatible.
Upstream patchelf losing compatibity [1] with Linux 5.17 and below.
This change was also picked up by Fedora 42, so we cannot update the
toolchain to that distribution until we have an alternative.
Here we add a minimal patchelf alternative. It was mostly written by
Claude. It is minimal in that it only supports --set-interpreter and
--print-interpreter, and works well enough for our needs. We still use
the original patchelf for --remove-rpath; this reduces our maintenance
needs.
[1] 43b75fbc9f
[2] 4b015255d1Closesscylladb/scylladb#24695
Whereas DynamoDB limits the names of tables, LSIs and GSIs to 255 characters each, Alternator currently has different (and lower) limitations:
1. A table name must be up to 222 characters.
2. For a GSI, the sum of the table's and GSI's name length, plus 1, must be up to 222 characters.
3. For an LSI, the sum of the table's and LSI's name length, plus 2, must be up to 222 characters.
The first patch documents these existing limitations, improves their testing, and fixes a tiny bug found by one of the tests (where UpdateTable adding a GSI's limit testing is off by one).
The second patch unfortunately shows with a reproducer (issue #24598) this limit of 222 is problematic and we may need to lower it: If a user creates a table of length 222 and then enables Alternator streams, Scylla shuts down on an IO error. This will need to be fixed later, but at least this patch properly documents the existing behavior.
No need to backport this patch - it is a very minor improvement that it is unlikely users care about and there is no potential for harm.
Closesscylladb/scylladb#24597
* github.com:scylladb/scylladb:
test/alternator: reproducer for streams bug with long table name
alternator: improve, document and test table/index name lengths
Although valid for compact tables, non-full (or empty) clustering key prefixes are not handled for row keys when writing sstables. Only the present components are written, consequently if the key is empty, it is omitted entirely.
When parsing sstables, the parsing code unconditionally parses a full prefix.
This mis-match results in parsing failures, as the parser parses part of the row content as a key resulting in a garbage key and subsequent mis-parsing of the row content and maybe even subsequent partitions.
Introduce a new system table: `system.corrupt_data` and infrastructure similar to `large_data_handler`: `corrupt_data_handler` which abstracts how corrupt data is handled. The sstable writer now passes rows such corrupt keys to the corrupt data handler. This way, we avoid corrupting the sstables beyond parsing and the rows are also kept around in system.corrupt_data for later inspection and possible recovery.
Add a full-stack test which checks that rows with bad keys are correctly handled.
Fixes: https://github.com/scylladb/scylladb/issues/24489
The bug is present in all versions, has to be backported to all supported versions.
Closesscylladb/scylladb#24492
* github.com:scylladb/scylladb:
test/boost/sstable_datafile_test: add test for corrupt data
sstables/mx/writer: handler rows with empty keys
test/lib/cql_assertions: introduce columns_assertions
sstables: add corrupt_data_handler to sstables::sstables
tools/scylla-sstable: make large_data_handler a local
db: introduce corrupt_data_handler
mutation: introduce frozen_mutation_fragment_v2
mutation/mutation_partition_view: read_{clustering,static}_row(): return row type
mutation/mutation_partition_view: extract de-ser of {clustering,static} row
idl-compiler.py: generate skip() definition for enums serializers
idl: extract full_position.idl from position_in_partition.idl
db/system_keyspace: add apply_mutation()
db/system_keyspace: introduce the corrupt_data table
Make sure the keys are full prefixes as it is expected to be the case for rows. At severeal occasions we have seen empty row keys make their ways into the sstables, despite the fact that they are not allowed by the CQL frontend. This means that such empty keys are possibly results of memory corruption or use-after-{free,copy} errors. The source of the corruption is impossible to pinpoint when the empty key is discovered in the sstable. So this patch adds checks for such keys to places where mutations are built: when building or unserializing mutations.
Fixes: https://github.com/scylladb/scylladb/issues/24506
Not a typical backport candidate (not a bugfix or regression fix), but we should still backport so we have the additional checks deployed to existing production clusters.
Closesscylladb/scylladb#24497
* github.com:scylladb/scylladb:
mutation: check key of inserted rows
compound: optimize is_full() for single-component types
The get_schema_versions handler gets unordered_map from storage service,
then converts it to API returning type, which is a vector. This vector
can be reserved, the final number of elements is known in advance.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#24715
The two tests in this patch reproduce issue #24598: When enabling
Alternator streams on an Alternator table with a very long name,
such as the maximum allowed name length 222, the result is an
I/O error and a Scylla shutdown.
The two tests are currently marked "skip", otherwise they would
crash the Scylla being tested.
Refs #24598
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Whereas DynamoDB limits the names of tables, LSIs and GSIs to 255
characters each, Alternator currently has different (and lower)
limitations:
1. A table name must be up to 222 characters.
2. For a GSI, the sum of the table's and GSI's name length, plus 1,
must be up to 222 characters.
3. For an LSI, the sum of the table's and LSI's name length, plus 2,
must be up to 222 characters.
These specific limitations were never documented, so in this patch we
add this information to docs/alternator/compatibility.md.
Moreover, these limitations where only partially tested, so in this patch
we add testing for more cases that we forgot to check - such as length
of LSI names (only GSI were checked before this patch), or adding a
GSI to an existing table. It is important to check all these corner
cases because there is a risk that if we attempt to create a table
without checking its length, we can end up with an I/O error that brings
down Scylla.
In one case - UpdateTable adding a GSI to an existing table - the new
test exposed a trivial bug: Because UpdateTable wants to verify the new
GSI doesn't have the same name as an existing LSI, it mistakenly applied
the LSI's length name limit instead of the GSI's name length limit,
which is one byte less than it should be. So this patch fixes this
trivial bug as well.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Previously, if test execution was cancelled, `run_all_tests()` could
return `None`. This caused a `TypeError` when the result was
unconditionally unpacked into `total_tests_pytest, failed_pytest_tests`.
This commit updates the code to handle the cancellation appropriately,
preventing the confusing `TypeError` exception and ensuring clean
cancellation behavior.
Closesscylladb/scylladb#24624
Audit component defines `audit` logger which it uses only for `error` and `info` logs,
regarding `audit` module initialization and errors during audit log writing.
This change introduces `debug` level logs on the happy path of audit log writes.
Fixes: https://github.com/scylladb/scylladb/issues/23773
No backport needed - this is a small quality-of-life improvement.
Closesscylladb/scylladb#24658
* github.com:scylladb/scylladb:
audit: change audit test logger level to `debug`
audit: introduce debug level logs on happy path
This commit fixes incorrect headings in the Admin Guide and the files
that are included in that guide.
The purpose is to properly organize the content and improve the search,
as well as prevent potential build problems caused by a poor heading organization.
Fixes https://github.com/scylladb/scylladb/issues/24441Closesscylladb/scylladb#24700
Audit module tests should show the `debug` level messages.
This change makes audit_test.py `audit` module log level to `debug`.
Closesscylladb/scylladb#23773
Audit component defines `audit` logger which it uses only for `error` and `info` logs,
regarding `audit` module initialization and errors during audit log writing.
This change introduces `debug` level logs on the happy path of audit log writes.
Ref: scylladb/scylladb#23773
This test asserts that a read repair really happened. To ensure this
happens it writes a single partition after enabling the database_apply
error injection point. For some reason, the write is sometimes reordered
with the error injection and the write will get replicated to both nodes
and no read repair will happen, failing the test.
To make the test less sensitive to such rare reordering, add a
clustering column to the table and write a 100 rows. The chance of *all*
100 of them being reordered with the error injection should be low
enough that it doesn't happen again (famous last words).
Fixes: #24330Closesscylladb/scylladb#24403
Add run ID for process output file to be not overwritten in the next case: first run failed, second passed. They are using the same name, so the second run will overwrite and delete the file. This will help to investigate in case of C++ test fails
Add attaching Scylla log files to allure report in case test failed. This is an alternative for link in JUnit report that exists in CI. That change will help to investigate the cluster tests fails. Example can be found in the failed [job](https://jenkins.scylladb.com/job/scylla-master/job/byo/job/byo_build_tests_dtest/2980/allure/).
Backport is not needed, this is only framework enhancements
Closesscylladb/scylladb#24677
* github.com:scylladb/scylladb:
test.py: Attach node logs in allure report in case of fail
test.py: Add run id to the boost output file
We replace the documentation of the old recovery procedure with the
documentation of the new recovery procedure.
The new recovery procedure requires the Raft-based topology to be
enabled, so to remove the old procedure from the documentation,
we must assume users have the Raft-based topology enabled.
We can do it in 2025.2 because the upgrade guides to 2025.1 state that
enabling the Raft-based topology is a mandatory step of the upgrade.
Another reminder is the upgrade guides to 2025.2.
Since we rely on the Raft-based topology being enabled, we remove the
obsolete parts of the documentation.
We will make the Raft-based topology mandatory in the code in the
future, hopefully in 2025.3. For this reason, we also don't touch the
dev docs in this PR.
Fixesscylladb/scylladb#24530
Requires backport to 2025.2 because 2025.2 contains the new recovery
procedure.
Closesscylladb/scylladb#24583
* github.com:scylladb/scylladb:
docs: rely on the Raft-based topology being enabled
docs: handling-node-failures: document the new recovery procedure
After paxos state is repaired in begin_and_repair_paxos we need to
re-check the state regardless if write back succeeded or not. This
is how the code worked originally but it was unintentionally changed
when co-routinized in 61b2e41a23.
Fixes#24630Closesscylladb/scylladb#24651
This patchset fixes regression introduced by 7e749cd848 when we started re-creating default superuser role and password from the config, even if new custom superuser was created by the user.
Now we'll check, first with CL LOCAL_ONE if there is a need to create default superuser role or password, confirm
it with CL QUORUM and only then atomically create role or password.
If server is started without cluster quorum we'll skip creating role or password.
Fixes https://github.com/scylladb/scylladb/issues/24469
Backport: all versions since 2024.2
Closesscylladb/scylladb#24451
* github.com:scylladb/scylladb:
test: auth_cluster: add test for password reset procedure
auth: cache roles table scan during startup
test: auth_cluster: add test for replacing default superuser
test: pylib: add ability to specify default authenticator during server_start
test: pylib: allow rolling restart without waiting for cql
auth: split auth-v2 logic for adding default superuser password
auth: split auth-v2 logic for adding default superuser role
auth: ldap: fix waiting for underlying role manager
auth: wait for default role creation before starting authorizer and authenticator
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
In 2025.2, we don't force enabling the Raft-based topology in the code,
but we stated in the upgrade guides that it's a mandatory step of the
upgrade to 2025.1. We also remind users to enable the Raft-based
topology in the upgrade guides to 2025.2. Hence, we can rely in the
the documentation on the Raft-based topology being enabled. If it is
still disabled, we can just send the user to the upgrade guides. Hence:
- we remove all documentation related to enabling the Raft-based
topology, enabling the Raft-based schema (enabled Raft-based topology
implies enabled Raft-based schema), and the gossip-based topology,
- we can replace the documentation of the old manual recovery procedure
with the documentation of the new manual recovery procedure (done in
the previous commit).
We replace the documentation of the old recovery procedure with the
documentation of the new recovery procedure.
We can get rid of the old procedure from the documentation because
we requested users to enable the Raft-based topology during upgrades to
2025.1 and 2025.2.
We leave the note that enabling the Raft-based topology is required to
use the new recovery procedure just in case, since we didn't force
enabling the Raft-based topology in the code.
To avoid overwriting the output tests adding the run id to it.
Previously, when first repeat failed and the second passes, because the
are using the same name for the output, it will be overwritten and
deleted since the second repeat passed
It may be particularly beneficial during connection
storms on startup. In such cases, it can happen that
none of the user's read requests succeed, preventing
the cache from being populated. This, in turn, makes
it more difficult for subsequent reads to
succeed, reducing resiliency against such storms.
Waiting for CQL requires default superuser being present
in db. In some cases we may delete it and still want to do
rolling restart. Additionally if we need CQL we may want to
wait after restart is complete (once, and not for each node).
In raft mode (auth-v2) we need to do atomic write after read as
we give stricter consistency guarantees. Instead of patching
legacy logic this commit adds different path as:
- old code may be less tested now so it's best to not change it
- new code path avoids quorum selects in a typical flow (passwords set)
There may be a case when user deletes a superuser or password
right before restarting a node, in such case we may ommit
updating a password but:
- this is a trade-off between quorum reads on startup
- it's far more important to not update password when it shouldn't be
- if needed password will be updated on next node restart
If there is no quorum on startup we'll skip creating password
because we can't perform any raft operation.
Additionally this fixes a problem when password is created despite
having non default superuser in auth-v2.
In raft mode (auth-v2) we need to do atomic write after read as
we give stricter consistency guarantees. Instead of patching
legacy logic this commit adds different path as:
- old code may be less tested now so it's best to not change it
- new code path avoids quorum selects in a typical flow (roles set)
This fixes a problem when superuser role is created despite
having non default superuser in auth-v2.
If there is no quorum on startup we'll skip creating role
because we can't perform any raft operation.
ldap_role_manager depends on standard_role_manager,
therefore it needs to wait for superuser initialization.
If this is missing, the password authenticator will start
checking the default password too early and may fail to
create the default password if there is no default
role yet.
Currently password authenticator will create password
together with the role in such case but in following
commits we want to separate those responsibilities correctly.
There is a hidden dependency: the creation of the default superuser role
is split between the password authenticator and the role manager.
To work correctly, they must start in the right order: role manager first,
then password authenticator.
The primary motivation for this change is to reduce the time during which the Effective Replication Map (ERM) is retained by the mapreduce service. This ensures that long aggregate queries do not block topology operations. As ScyllaDB is generally transitioning towards tablets, and using tablets simplifies work dispatching, the decision was made to design the new algorithm specifically for tablets. The goal of the algorithm is to divide the work in such a way that each `tablet_replica` (that is <host, shard> pair) processes two tablets at a time.
The new algorithm can be summarized as follows:
1. Prepare a tablet_replica -> partition_range mapping where the values cover the entire space.
2. For each tablet_replica, in parallel, take two partition ranges and dispatch them to the node hosting the replica. The ERM is released and re-acquired in each iteration, allowing the destination (i.e., tablet_replica) to change for each
artition range (in such cases, the partition range is assigned to the appropriate tablet_replica).
In step 1, the main difference compared to the old algorithm (dispatch_to_vnodes) is that partition ranges are assigned to a tablet_replica rather than just the host.
In step 2, the main difference is that the work is divided into smaller batches, and the ERM is released and re-acquired for each batch.
In the current implementation, each node can correctly handle every partition range, even if the mapreduce supercoordinator does not retain the ERM and the range is absent locally. This is because mapreduce_service::execute_on_this_shard creates a new pager that coordinates the partition range read, including obtaining its own ERM. However, every partition range that is absent locally is handled by shard 0. Therefore, proper routing of partition ranges is necessary to avoid shard 0 overload. This is why, in step 2, the ERM is retained during each batch processing, and the tablet_replica is refreshed for each processed range.
Additionally, shard_id is added to mapreduce request. When shard_id is set, the entire partition range is handled by the specified shard. As the new tablet-aware mapreduce algorithm balances the workload across shards, shard_id ensure that the balance is preserved, even during events such as tablet splits.
This patch series:
- Refactors a bit mapreduce service, to facilitate having two algorithm versions (one for vnodes and one for tablets).
- Implements tablet-aware dispatching algorithm.
- Adds shard_id to mapreduce request and uses the information to handle requests entirely by selected shard.
- Adds test_long_query_timeout_erm to verify the new functionality.
Fixes: scylladb#21831
No backport, as it is rather new feature than a bugfix.
Closesscylladb/scylladb#24383
* github.com:scylladb/scylladb:
mapreduce: add missing comma and space in mapreduce_request operator<<
mapreduce: add shard_id_hint to mapreduce request
test: add test_long_query_timeout_erm
mapreduce: add tablet-aware dispatching algorithm
storage_proxy: make storage_proxy::is_alive public
mapreduce: remove _shared_token_metadata from mapreduce_service
mapreduce: move dispatching logic to dispatch_to_vnodes
mapreduce: remove underscores from variable names
mapreduce: move req_with_modified_pr handling to a new function
mapreduce: change next_vnode lambda to get_next_partition_range function
Before we can eradicate the numerical sstable generations,
This series completes https://github.com/scylladb/scylladb/issues/20337
by disabling the use of numerical sstable generations where we can
and making sure the feature is never disabled.
Note that until the cluster feature is enabled in the startup process on first boot, numerical generation might be used for local system tables.
Refs #24248
* Enhancement. No backport required
Closesscylladb/scylladb#24554
* github.com:scylladb/scylladb:
feature_service: never disable UUID_SSTABLE_IDENTIFIERS
test: sstable_move_test: always use uuid sstable generation
test: sstable_directory_test: always use uuid sstable generation
sstables: sstable_generation_generator: set last_generation=0 by default
test: database_test: test_distributed_loader_with_pending_delete: use uuid sstable generation
test: lib: test_env: always use uuid sstable generation
test: sstable_test: always use uuid sstable generation
test: sstable_resharding_test::sstable_resharding_over_s3_test: use default use_uuid in config
test: sstable_datafile_test: compound_sstable_set_basic_test: use uuid sstable generation
test: sstable_compaction_test: always use uuid sstable generation
It solves the issue, where in some cases a timeout exceptions in CAS operations are logged incorrectly as a general failure.
Fixes#24591Closesscylladb/scylladb#24619
Some tests want to switch between sched groups. For that there's
cql-test-env facility to create and use them. However, there's a test
that uses replica::database as sched groups provider, which is not nice.
Fix it.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#24615
Introduce `sstables::parse_assert()`, to replace `SCYLLA_ASSERT()` on the read/parse path. SSTables can get corrupt for various reasons, some outside of the database's control. A bad SSTable should not bring down the database, the parsing should simply be aborted, with as much information printed as possible for the investigation of the nature of the corruption. The newly introduced `parse_assert()` uses `on_internal_error()` under the hood, which prints a backtrace and optionally allows for aborting when on the error, to generate a coredump.
Fixes https://github.com/scylladb/scylladb/issues/20845
We just hit another case of `SCYLLA_ASSERT()` triggering due to corrupt sstables bringing down nodes in the field, should be backported to all releases, so we don't hit this in the future
Closesscylladb/scylladb#24534
* github.com:scylladb/scylladb:
sstables: replace SCYLLA_ASSERT() with parse_assert() on the read path
sstables/exceptions: introduce parse_assert()
When writing large partitions, that is: partitions with size or row count
above a configurable threshold, ScyllaDB outputs a warning to the log:
WARN ... large_data - Writing large partition test/test: (1200031 bytes) to me-3glr_0xkd_54jip2i8oqnl7hk8mu-big-Data.db
This warning contains the information about the size of the partition,
but it does not contain the number of rows written. This can lead to
confusion because in cases where the warning was written because of the
row count being larger than the threshold, but the partition size is below
the threshold, the warning will only contain the partition size in bytes,
leading the user to believe the warning was output because of the
partition size, when in reality it was the row count that triggered the
warning. See #20125
This change adds a size_desc argument to cql_table_large_data_handler::try_record(),
which will contain the description of the size of the object written.
This method is used to output warnings for large partitions, row counts,
row sizes and cell sizes. This change does not modify the warning message
for row and cell sizes, only for partition size and row count.
The warning for large partitions and row counts will now look like this:
WARN ... large_data - Writing large partition test/test: (1200031 bytes/100001 rows) to me-3glr_0xkd_54jip2i8oqnl7hk8mu-big-Data.db
Closesscylladb/scylladb#22010
This is not needed on clean disks, which is often the case with cloud instances, but can be useful on bare metal servers with disks that were used before.
Therefore, the default is to skip blkdiscard operation, which makes overall installation faster.
If the user wishes to run it anyway, use the newly introduced --blkdiscard option of scylla_raid_setup to perform it.
Note: since we either perform online discard or schedule fstrim, the (previously used) space will gradually get trimmed, this way or another.
Fixes: https://github.com/scylladb/scylladb/issues/24470
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
Closesscylladb/scylladb#24579
In ed3e4f33fd we introduced new connection throttling feature which is controlled by uninitialized_connections_semaphore_cpu_concurrency config. But live updating of it was broken, this patch fixes it.
When the temporary value from observer() is destroyed, it disconnects from updateable_value, so observation stops right away. We need to retain the observer.
Backport: to 2025.2 where this feature was added
Fixes: https://github.com/scylladb/scylladb/issues/24557Closesscylladb/scylladb#24484
* github.com:scylladb/scylladb:
test: add test for live updates of generic server config
utils: don't allow do discard updateable_value observer
generic_server: fix connections semaphore config observer
