ef43531fb6
Although Cassandra generally does not allow empty strings as partition keys (note they are allowed as clustering keys!), it *does* allow empty strings in regular columns to be indexed by a secondary index, or to become an empty partition-key column in a materialized view. As noted in issues #9375 and #9364 and verified in a few xfailing cql-pytest tests, Scylla didn't allow these cases - and this patch fixes that. The patch mostly *removes* unnecessary code: In one place, code prevented an sstable with an empty partition key from being written. Another piece of removed code was a function is_partition_key_empty() which the materialized-view code used to check whether the view's row will end up with an empty partition key, which was supposedly forbidden. But in fact, should have been allowed like they are allowed in Cassandra and required for the secondary-index implementation, and the entire function wasn't necessary. Note that the removed function is_partition_key_empty() was *NOT* required for the "IS NOT NULL" feature of materialized views - this continues to work as expected after this patch, and we add another test to confirm it. Being null and being an empty string are two different things. This patch also removes a part of a unit test which enshrined the wrong behavior. After this patch we are left with one interesting difference from Cassandra: Though Cassandra allows a user to create a view row with an empty-string partition key, and this row is fully visible in when scanning the view, this row can *not* be queried individually because "WHERE v=''" is forbidden when v is the partition key (of the view). Scylla does not reproduce this anomaly - and such point query does work in Scylla after this patch. We add a new test to check this case, and mark it "cassandra_bug", i.e., it's a Cassandra behavior which we consider wrong and don't want to emulate. This patch relies on #9352 and #10178 having been fixed in previous patches, otherwise the WHERE v='' does not work when reading from sstables. We add to the already existing tests we had for empty materialized-views keys a lookup with WHERE v='' which failed before fixing those two issues. Fixes #9364 Fixes #9375 Signed-off-by: Nadav Har'El <nyh@scylladb.com>
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 users mailing list 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.