202f16e799
This series introduces workload prioritization: an extension of the service levels feature which allows specifying "shares" per service level. The number of shares determines the priority of the user which has this service level attached (if multiple are attached then the one with the lowest shares wins). Different service levels will be isolated in the following way: - Each service level gets its own scheduling group with the number of shares (corresponding to the service level's number of shares), which controls the priority of the CPU and I/O used for user operations running on that service level. - Each service level gets two reader concurrency semaphores, one for user reads and the other for read-before-write done for view updates. - Each service level gets its own TCP connections for RPC to prevent priority inversion issues. Because of the mandatory use of scheduling groups, which are a globally limited resource, the number of service levels is now limited to 7 user created service levels + 1 created by default that cannot be removed. This feature has been previously only available in ScyllaDB Enterprise but has been made available for the source available ScyllaDB. The series was created by comparing the master branch with source-available-workbranch / enterprise branch and taking the workload prioritization related parts from the diff, then molding the resulting diff into a proper series. Some very minor changes were made such as fixing whitespace, removing unused or unnecessary code, adding some boilerplate (in api/) which was missing, but otherwise no major changes have been made. No backport is required. Closes scylladb/scylladb#22031 * github.com:scylladb/scylladb: tracing: record scheduling group in trace event record qos: un-shared-from-this standard_service_level_distributed_data_accessor alternator: execute under scheduling group for service level test.py: support multiple commands in prepare_cql in suite.yml docs: add documentation for workload prioritization docs/dev: describe workload prioritization features in service_levels test/auth_cluster: test workload prioritization in service level tests cqlpy/test_service_levels: add workload prioritization tests api: introduce service levels specific API api/cql_server_test: add information about scheduling group db/virtual_tables: add scheduling group column to system.clients test/boost: update service_level_controller_test for workload prio qos: include number of shares in DESCRIBE cql3/statements: update SL statements for workload prioritization transport/server: use scheduling group assigned to current user messaging_service: use separate set of connections per service levels replica/database: add reader concurrency semaphore groups qos: manage and assign scheduling groups to service levels qos: use the shares field in service level reads/writes qos: add shares to service_level_options qos: explicitly specify columns when querying service level tables db/system_distributed_keyspace: add shares column and upgrade code db/system_keyspace: adjust SL schema for workload prioritization gms: introduce WORKLOAD_PRIORITIZATION cluster feature build: increase the max number of scheduling groups qos: return correct error code when SL does not exist
Scylla developer documentation
This folder contains developer-oriented documentation concerning the ScyllaDB codebase. We also have a wiki, which contains additional developer-oriented documentation. There is currently no clear definition of what goes where, so when looking for something be sure to check both.
Seastar documentation can be found here.
User documentation can be found on docs.scylladb.com
For information on how to build Scylla and how to contribute visit HACKING.md and CONTRIBUTING.md.