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The test dtest materialized_views_test.py::TestMaterializedViews:: test_mv_populating_from_existing_data_during_truncate reproduces an assertion failure, and crash, while doing a CREATE MATERIALIZED VIEW during a TRUNCATE operation. This patch fixes the crash by removing the assert() call for a view (replacing it by a warning message) - we'll explain below why this is fine. Also for base tables change we change the assertion to an on_internal_error (Refs #7871). This makes the test stop crashing Scylla, but it still fails due to issue #17635. Let's explain the crash, and the fix: The test starts TRUNCATE on table that doesn't yet have a view. truncate_table_on_all_shards() begins by disabling compaction on the table and all its views (of which there are none, at this point). At this point, the test creates a new view is on this table. The new view has, by default, compaction enabled. Later, TRUNCATE calls discard_sstables() on this new view, asserts that it has compaction disabled - and this assertion fails. The fix in this patch is to not do the assert() for views. In other words, we acknowledge that in this use case, the view *will* have compactions enabled while being truncated. I claim that this is "good enough", if we remember *why* we disable compaction in the first place: It's important to disable compaction while truncating because truncating during compaction can lead us to data resurection when the old sstable is deleted during truncation but the result of the compaction is written back. True, this can now happen in a new view (a view created *DURING* the truncation). But I claim that worse things can happen for this new view: Notably, we may truncate a view and then the ongoing view building (which happens in a new view) might copy data from the base to the view and only then truncate the base - ending up with an empty base and non-empty view. This problem - issue #17635 - is more likely, and more serious, than the compaction problem, so will need to be solved in a separate patch. Fixes #17543. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Closes scylladb/scylladb#17634
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++20 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 APIs - CQL and Thrift. 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 the ScyllaDB open source.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.