03818c4aa9
The direct failure detector design is simplistic. It sends pings sequentially and times out listeners that reached the threshold (i.e. didn't hear from a given endpoint for too long) in-between pings. Given the sequential nature, the previous ping must finish so the next ping can start. We timeout pings that take too long. The timeout was hardcoded and set to 300ms. This is too low for wide-area setups -- latencies across the Earth can indeed go up to 300ms. 3 subsequent timed out pings to a given node were sufficient for the Raft listener to "mark server as down" (the listener used a threshold of 1s). Increase the ping timeout to 600ms which should be enough even for pinging the opposite side of Earth, and make it tunable. Increase the Raft listener threshold from 1s to 2s. Without the increased threshold, one timed out ping would be enough to mark the server as down. Increasing it to 2s requires 3 timed out pings which makes it more robust in presence of transient network hiccups. In the future we'll most likely want to decrease the Raft listener threshold again, if we use Raft for data path -- so leader elections start quickly after leader failures. (Faster than 2s). To do that we'll have to improve the design of the direct failure detector. Ref: scylladb/scylladb#16410 Fixes: scylladb/scylladb#16607 --- I tested the change manually using `tc qdisc ... netem delay`, setting network delay on local setup to ~300ms with jitter. Without the change, the result is as observed in scylladb/scylladb#16410: interleaving ``` raft_group_registry - marking Raft server ... as dead for Raft groups raft_group_registry - marking Raft server ... as alive for Raft groups ``` happening once every few seconds. The "marking as dead" happens whenever we get 3 subsequent failed pings, which is happens with certain (high) probability depending on the latency jitter. Then as soon as we get a successful ping, we mark server back as alive. With the change, the phenomenon no longer appears. Closes scylladb/scylladb#18443
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.