312a417060
The test `test_sync_point` had a few shortcomings that made it flaky
or simply wrong:
1. We were verifying that hints were written by checking the size of
in-flight hints. However, that could potentially lead to problems
in rare situations.
For instance, if all of the hints failed to be written to disk, the
size of in-flight hints would drop to zero, but creating a sync point
would correspond to the empty state.
In such a situation, we should fail immediately and indicate what
the cause was.
2. A sync point corresponds to the hints that have already been written
to disk. The number of those is tracked by the metric `written`.
It's a much more reliable way to make sure that hints have been
written to the commitlog. That ensures that the sync point we'll
create will really correspond to those hints.
3. The auxiliary function `wait_for` used in the test works like this:
it executes the passed callback and looks at the result. If it's
`None`, it retries it. Otherwise, the callback is deemed to have
finished its execution and no further retries will be attempted.
Before this commit, we simply returned a bool, and so the code was
wrong. We improve it.
---
Note that this fixes scylladb/scylladb#28203, which was a manifestation
of scylladb/scylladb#25879. We created a sync point that corresponded
to the empty state, and so it immediately resolved, even when node 3
was still dead.
As a bonus, we rewrite the auxiliary code responsible for fetching
metrics and manipulating sync points. Now it's asynchronous and
uses the existing standard mechanisms available to developers.
Furthermore, we reduce the time needed for executing
`test_sync_point` by 27 seconds.
---
The total difference in time needed to execute the whole test file
(on my local machine, in dev mode):
Before:
CPU utilization: 0.9%
real 2m7.811s
user 0m25.446s
sys 0m16.733s
After:
CPU utilization: 1.1%
real 1m40.288s
user 0m25.218s
sys 0m16.566s
---
Refs scylladb/scylladb#25879
Fixes scylladb/scylladb#28203
Backport: This improves the stability of our CI, so let's
backport it to all supported versions.
- (cherry picked from commit 628e74f157)
- (cherry picked from commit ac4af5f461)
- (cherry picked from commit c5239edf2a)
- (cherry picked from commit a256ba7de0)
- (cherry picked from commit f83f911bae)
Parent PR: #28602
Closes scylladb/scylladb#28620
* github.com:scylladb/scylladb:
test: topology_custom: Reduce wait time in test_sync_point
test: topology_custom: Fix test_sync_point
test: topology_custom: Await sync points asynchronously
test: topology_custom: Create sync points asynchronously
test: topology_custom: Fetch hint metrics asynchronously
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 the ScyllaDB open source.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.