5feed00caa
When the local entry with `read_idx` belongs to the current term, it's
safe to update the local `commit_idx` to `read_idx`.
The motivation for this change is to speed up read barriers. `wait_for_apply`
executed at the end of `read_barrier` is delayed until the follower learns
that the entry with `read_idx` is committed. It usually happens quickly in
the `read_quorum` message. However, non-voters don't receive this message,
so they have to wait for `append_entries`. If no new entries are being
added, `append_entries` can come only from `fsm::tick_leader()`. For group0,
this happens once every 100ms.
The issue above significantly slows down cluster setups in tests. Nodes
join group0 as non-voters, and then they are met with several read barriers
just after a write to group0. One example is `global_token_metadata_barrier`
in `write_both_read_new` performed just after `update_topology_state` in
`write_both_read_old`.
I tested the performance impact of this change with the following test:
```python
for _ in range(10):
await manager.servers_add(3)
```
It consistently takes 44-45s with the change and 50-51s without the change
in dev mode.
No backport:
- non-critical performance improvement mostly relevant in tests,
- the change requires some soak time in master.
Closes scylladb/scylladb#28891
* github.com:scylladb/scylladb:
raft: server: fix the repeating typo
raft: clarify the comment about read_barrier_reply
raft: read_barrier: update local commit_idx to read_idx when it's safe
raft: log: clarify the specification of term_for
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.