bbcf8305bb
Before this commit the `wait_for_normal_state_handled_on_boot` would
wait for a static set of nodes (`sync_nodes`), calculated using the
`get_nodes_to_sync_with` function and `parse_node_list`; the latter was
used to obtain a list of "nodes to ignore" (for replace operation) and
translate them, using `token_metadata`, from IP addresses to Host IDs
and vice versa. `sync_nodes` was also used in `_gossiper.wait_alive` call
which we do after `wait_for_normal_state_handled_on_boot`.
Recently we started doing these calculations and this wait very early in
the boot procedure - immediately after we start gossiping
(50e8ec77c6).
Unfortunately, as always with gossiper, there are complications.
In #14468 and #14487 two problems were detected:
- Gossiper may contain obsolete entries for nodes which were recently
replaced or changed their IPs. These entries are still using status
`NORMAL` or `shutdown` (which is treated like `NORMAL`, e.g.
`handle_state_normal` is also called for it). The
`_gossiper.wait_alive` call would wait for those entries too and
eventually time out.
- Furthermore, by the time we call `parse_node_list`, `token_metadata`
may not be populated yet, which is required to do the IP<->Host ID
translations -- and populating `token_metadata` happens inside
`handle_state_normal`, so we have a chicken-and-egg problem here.
The `parse_node_list` problem is solved in this commit. It turns out
that we don't need to calculate `sync_nodes` (and hence `ignore_nodes`)
in order to wait for NORMAL state handlers. We can wait for handlers to
finish for *any* `NORMAL`/`shutdown` entries appearing in gossiper, even
those that correspond to dead/ignored nodes and obsolete IPs.
`handle_state_normal` is called, and eventually finishes, for all of
them. `wait_for_normal_state_handled_on_boot` no longer receives a set
of nodes as parameter and is modified appropriately, it's now
calculating the necessary set of nodes on each retry (the set may shrink
while we're waiting, e.g. because an entry corresponding to a node that
was replaced is garbage-collected from gossiper state).
Thanks to this, we can now put the `sync_nodes` calculation (which is
still necessary for `_gossiper.wait_alive`), and hence the
`parse_node_list` call, *after* we wait for NORMAL state handlers,
solving the chickend-and-egg problem.
This addresses the immediate failure described in #14487, but the test
will still fail. That's because `_gossiper.wait_alive` may still receive
a too large set of nodes -- we may still include obsolete IPs or entries
corresponding to replaced nodes in the `sync_nodes` set. We fix this
in the following commit which will solve both issues.
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.