e6137ab11b
table_helper::insert() retrieves the prepared statement via cache_table_info() and then dereferences _prepared_stmt to read bound_names. _prepared_stmt is a checked_weak_ptr into the prepared statements cache and can be invalidated at any time by a concurrent purge (for example, on a schema change). cache_table_info() (re-)prepares the statement and assigns _prepared_stmt before returning, and the strong pin held by the result_message::prepared returned from qp.prepare() keeps the cache entry alive only for the duration of try_prepare(). After try_prepare() returns, the pin is gone and _prepared_stmt is the only remaining handle on the entry. In release builds this is fine: the chain of ready-future co_awaits between try_prepare() finishing and _prepared_stmt->bound_names being read resumes synchronously, so no other task -- in particular, no cache purge -- can run in that window. In debug builds, however, Seastar inserts a reactor preemption point on every co_await even when the awaited future is ready. That preemption window is wide enough for a concurrent invalidation to drop the freshly installed cache entry, turning _prepared_stmt into a null weak handle and crashing the subsequent dereference with checked_ptr_is_null_exception. Wrap the cache_table_info() call in a loop that re-attempts the preparation until a synchronous post-resume check finds _prepared_stmt still valid. The check runs in the same task immediately after the co_await resumes, with no co_await between the check and the dereference, so a purge cannot slip in. _insert_stmt is a strong shared_ptr to the statement object and is not affected by cache invalidation, so it remains safe to use across the final co_await on execute(). The other caller of cache_table_info(), trace_keyspace_helper::apply_events_mutation(), accesses only the strong _insert_stmt via insert_stmt() and never dereferences the weak _prepared_stmt, so it is unaffected. Refs SCYLLADB-1173
Scylla
What is Scylla?
Scylla is the real-time big data database that is API-compatible with Apache Cassandra and Amazon DynamoDB. Scylla embraces a shared-nothing approach that increases throughput and storage capacity to realize order-of-magnitude performance improvements and reduce hardware costs.
For more information, please see the ScyllaDB web site.
Build Prerequisites
Scylla is fairly fussy about its build environment, requiring very recent versions of the C++23 compiler and of many libraries to build. The document HACKING.md includes detailed information on building and developing Scylla, but to get Scylla building quickly on (almost) any build machine, Scylla offers a frozen toolchain. This is a pre-configured Docker image which includes recent versions of all the required compilers, libraries and build tools. Using the frozen toolchain allows you to avoid changing anything in your build machine to meet Scylla's requirements - you just need to meet the frozen toolchain's prerequisites (mostly, Docker or Podman being available).
Building Scylla
Building Scylla with the frozen toolchain dbuild is as easy as:
$ git submodule update --init --force --recursive
$ ./tools/toolchain/dbuild ./configure.py
$ ./tools/toolchain/dbuild ninja build/release/scylla
For further information, please see:
- Developer documentation for more information on building Scylla.
- Build documentation on how to build Scylla binaries, tests, and packages.
- Docker image build documentation for information on how to build Docker images.
Running Scylla
To start Scylla server, run:
$ ./tools/toolchain/dbuild ./build/release/scylla --workdir tmp --smp 1 --developer-mode 1
This will start a Scylla node with one CPU core allocated to it and data files stored in the tmp directory.
The --developer-mode is needed to disable the various checks Scylla performs at startup to ensure the machine is configured for maximum performance (not relevant on development workstations).
Please note that you need to run Scylla with dbuild if you built it with the frozen toolchain.
For more run options, run:
$ ./tools/toolchain/dbuild ./build/release/scylla --help
Testing
See test.py manual.
Scylla APIs and compatibility
By default, Scylla is compatible with Apache Cassandra and its API - CQL. There is also support for the API of Amazon DynamoDB™, which needs to be enabled and configured in order to be used. For more information on how to enable the DynamoDB™ API in Scylla, and the current compatibility of this feature as well as Scylla-specific extensions, see Alternator and Getting started with Alternator.
Documentation
Documentation can be found here. Seastar documentation can be found here. User documentation can be found here.
Training
Training material and online courses can be found at Scylla University. The courses are free, self-paced and include hands-on examples. They cover a variety of topics including Scylla data modeling, administration, architecture, basic NoSQL concepts, using drivers for application development, Scylla setup, failover, compactions, multi-datacenters and how Scylla integrates with third-party applications.
Contributing to Scylla
If you want to report a bug or submit a pull request or a patch, please read the contribution guidelines.
If you are a developer working on Scylla, please read the developer guidelines.
Contact
- The community forum and Slack channel are for users to discuss configuration, management, and operations of ScyllaDB.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.