f89f4e69a0
Fixes #8270
If we have an allocation pattern where we leave large parts of segments "wasted" (typically because the segment has empty space, but cannot hold the mutation being added), we can have a disk usage that is below threshold, yet still get a disk footprint that is over limit causing new segment allocation to stall.
We need to take a few things into account:
1.) Need to include wasted space in the threshold check. Whether or not disk is actually used does not matter here.
2.) If we stall a segment alloc, we should just flush immediately. No point in waiting for the timer task.
3.) Need to adjust the thresholds a bit. Depending on sizes, we should probably consider start flushing once we've used up space enough to be in the last available segment, so a new one is hopefully available by the time we hit the limit.
4.) (v2) Must ensure discard/delete routines are executed. Because we can race with background disk syncs, we may need to
issue segment prunes from end_flush() so we wake up actual file deletion/recycling
5.) (v2) Shutdown must ensure discard/delete is run after we've disabled background task etc, otherwise we might fail waking up replenish and get stuck in gate
6.) (v2) Recycling or deleting segments must be consistent, regardless of shutdown. For same reason as above.
7.) (v3) Signal recycle/delete queues/promise on shutdown (with recognized marker) to handle edge case where we only have a single (allocating) segment in the list, and cannot wake up replenisher in any more civilized way.
Also fix edge case (for tests), when we have too few segment to have an active one (i.e. need flush everything).
New attempt at this, should fix intermittent shutdown deadlocks in commitlog_test.
Closes #8764
* github.com:scylladb/scylla:
commitlog_test: Add test case for usage/disk size threshold mismatch
commitlog_test: Improve test assertion
commitlog: Add waitable future for background sync/flush
commitlog: abort queues on shutdown
commitlog: break out "abort" calls into member functions
commitlog: Do explicit discard+delete in shutdown
commitlog: Recycle or not should not depend on shutdown state
commitlog: Issue discard_unused_segments on segment::flush end IFF deletable
commitlog: Flush all segments if we only have one.
commitlog: Always force flush if segment allocation is waiting
commitlog: Include segment wasted (slack) size in footprint check
commitlog: Adjust (lower) usage threshold
(cherry picked from commit 14252c8b71)
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.