afe6b0d8c9
Currently we have no visibility into what happens to a read in the reader concurrency semaphore as far as tracing is concerned. This series fixes that, storing a trace state pointer on the reader permit and using it to add trace messages to important semaphore related events:
* admission decision
* execution (execution stage functionality)
* eviction
This allows for seeing if the read suffered any delay in the semaphore.
Example tracing (2 pages):
```
Tracing session: 8cc80d50-c72d-11ed-8427-14e21cc3ed56
activity | timestamp | source | source_elapsed | client
-------------------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------+----------------+-----------
Execute CQL3 query | 2023-03-20 10:43:16.773000 | 127.0.0.1 | 0 | 127.0.0.1
Parsing a statement [shard 0] | 2023-03-20 10:43:16.773754 | 127.0.0.1 | -- | 127.0.0.1
Processing a statement [shard 0] | 2023-03-20 10:43:16.773837 | 127.0.0.1 | 83 | 127.0.0.1
Creating read executor for token -4911109968640856406 with all: {127.0.0.1} targets: {127.0.0.1} repair decision: NONE [shard 0] | 2023-03-20 10:43:16.773874 | 127.0.0.1 | 121 | 127.0.0.1
read_data: querying locally [shard 0] | 2023-03-20 10:43:16.773877 | 127.0.0.1 | 123 | 127.0.0.1
Start querying singular range {{-4911109968640856406, pk{000d73797374656d5f736368656d61}}} [shard 0] | 2023-03-20 10:43:16.773881 | 127.0.0.1 | 128 | 127.0.0.1
[reader concurrency semaphore] admitted immediately [shard 0] | 2023-03-20 10:43:16.773884 | 127.0.0.1 | 130 | 127.0.0.1
[reader concurrency semaphore] executing read [shard 0] | 2023-03-20 10:43:16.773890 | 127.0.0.1 | 137 | 127.0.0.1
Querying cache for range {{-4911109968640856406, pk{000d73797374656d5f736368656d61}}} and slice {(-inf, +inf)} [shard 0] | 2023-03-20 10:43:16.773903 | 127.0.0.1 | 149 | 127.0.0.1
Page stats: 1 partition(s), 0 static row(s) (0 live, 0 dead), 100 clustering row(s) (100 live, 0 dead) and 0 range tombstone(s) [shard 0] | 2023-03-20 10:43:16.774674 | 127.0.0.1 | 920 | 127.0.0.1
Caching querier with key 5eff94d2-e47a-43b2-8e3a-2d80a9cc3b3e [shard 0] | 2023-03-20 10:43:16.774685 | 127.0.0.1 | 931 | 127.0.0.1
Querying is done [shard 0] | 2023-03-20 10:43:16.774688 | 127.0.0.1 | 934 | 127.0.0.1
Done processing - preparing a result [shard 0] | 2023-03-20 10:43:16.774706 | 127.0.0.1 | 953 | 127.0.0.1
Request complete | 2023-03-20 10:43:16.774225 | 127.0.0.1 | 1225 | 127.0.0.1
Tracing session: 8d26f630-c72d-11ed-8427-14e21cc3ed56
activity | timestamp | source | source_elapsed | client
---------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------+----------------+-----------
Execute CQL3 query | 2023-03-20 10:43:17.395000 | 127.0.0.1 | 0 | 127.0.0.1
Parsing a statement [shard 0] | 2023-03-20 10:43:17.395498 | 127.0.0.1 | -- | 127.0.0.1
Processing a statement [shard 0] | 2023-03-20 10:43:17.395558 | 127.0.0.1 | 60 | 127.0.0.1
Creating read executor for token -4911109968640856406 with all: {127.0.0.1} targets: {127.0.0.1} repair decision: NONE [shard 0] | 2023-03-20 10:43:17.395597 | 127.0.0.1 | 99 | 127.0.0.1
read_data: querying locally [shard 0] | 2023-03-20 10:43:17.395600 | 127.0.0.1 | 102 | 127.0.0.1
Start querying singular range {{-4911109968640856406, pk{000d73797374656d5f736368656d61}}} [shard 0] | 2023-03-20 10:43:17.395604 | 127.0.0.1 | 106 | 127.0.0.1
Found cached querier for key 5eff94d2-e47a-43b2-8e3a-2d80a9cc3b3e and range(s) {{{-4911109968640856406, pk{000d73797374656d5f736368656d61}}}} [shard 0] | 2023-03-20 10:43:17.395610 | 127.0.0.1 | 112 | 127.0.0.1
Reusing querier [shard 0] | 2023-03-20 10:43:17.395614 | 127.0.0.1 | 116 | 127.0.0.1
[reader concurrency semaphore] executing read [shard 0] | 2023-03-20 10:43:17.395622 | 127.0.0.1 | 125 | 127.0.0.1
Page stats: 1 partition(s), 0 static row(s) (0 live, 0 dead), 11 clustering row(s) (11 live, 0 dead) and 0 range tombstone(s) [shard 0] | 2023-03-20 10:43:17.395711 | 127.0.0.1 | 213 | 127.0.0.1
Querying is done [shard 0] | 2023-03-20 10:43:17.395718 | 127.0.0.1 | 221 | 127.0.0.1
Done processing - preparing a result [shard 0] | 2023-03-20 10:43:17.395734 | 127.0.0.1 | 236 | 127.0.0.1
Request complete | 2023-03-20 10:43:17.395276 | 127.0.0.1 | 276 | 127.0.0.1
```
Fixes: https://github.com/scylladb/scylladb/issues/12781
Closes #13255
* github.com:scylladb/scylladb:
reader_concurrency_semaphore: add trace points for important events
reader_permit: refresh trace_state on new pages
reader_permit: keep trace_state pointer on permit
test/perf/perf_collection: give more unique names to key comparators
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.