17075bf3f9
When encrypted_data_source::get() caches a trailing block in _next, the next call takes it directly — bypassing input_stream::read(), which checks _eof. It then calls input_stream::read_exactly() on the already-drained stream. Unlike read(), read_up_to(), and consume(), read_exactly() does not check _eof when the buffer is empty, so it calls _fd.get() on a source that already returned EOS.
In production this manifested as stuck encrypted SSTable component downloads during tablet restore: the underlying chunked_download_source hung forever on the post-EOS get(), causing 4 tablets to never complete. The stuck files were always block-aligned sizes (8k, 12k) where _next gets populated and the source is fully consumed in the same call.
Fix by checking _input.eof() before calling read_exactly(). When the stream already reached EOF, buf2 is known to be empty, so the call is skipped entirely.
A comprehensive test is added that uses a strict_memory_source which fails on post-EOS get(), reproducing the exact code path that caused the production deadlock.
Fixes: https://scylladb.atlassian.net/browse/SCYLLADB-1128
Backport to 2025.3/4 and 2026.1 is needed since it fixes a bug that may bite us in production, to be on the safe side
Closes scylladb/scylladb#29110
* github.com:scylladb/scylladb:
encryption: fix deadlock in encrypted_data_source::get()
Fix formatting after previous patch
Fix indentation after previous patch
(cherry picked from commit 3b9398dfc8)
Closes scylladb/scylladb#29198
Closes scylladb/scylladb#29359
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.