mirror of https://github.com/apache/cassandra
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Fairness: tasks are grouped by kind of work, and for each group we track work arrival and service via decaying counters. If work for some group(s) begin to be served at a much lower rate than some other group (e.g. because that group has a large backlog, that by simple priority comes first), then we begin processing some fraction of the work by service-ratio rather than priority. This means that we cannot starve request processing because, e.g., a sync point has produced thousands of state save tasks. Incremental processing: tasks that process many keys may be declared INCR or ASYNC. ASYNC indicates the keys are needed (so should be loaded), but may be used in follow-up work so the task may be executed if the data is not yet loaded. An ASYNC task may be followed by an INCR task that processes keys as they are loaded, with limits to the batch sizes. This limits the latency impact of processing larger transactions such as sync points. INCR tasks may be declared to be processed in either an arbitrary order with no isolation, or “atomically” with its parent task. In the latter case, the complete unit of work appears to execute as a single execution to external observers (blocking progress on unprocessed keys). Key-level ordering: AccordCacheEntry can inflate a special Queue object that can be used to impose ordering constraints: FIFO for atomic work (once it has been part processed, or submitted as part of a parent task); prioritised for tasks that have a key-level priority to impose (i.e. PreAccept/Accept/Commit/Stable/Apply want to be ordered by TxnId); and unsequenced tasks for those that have no sequencing restrictions. Additional improvements: - AccordCacheEntry are now explicitly LOCKED for the duration of their usage, which may span multiple executions for long running INCR tasks. - ExclusiveExecutor releases its ownership lock immediately, since AccordCacheEntry locks guarantee safety (as they will not be released until the task is cleaned up) - CassandraThread tracks active and locked AccordExecutor, so that we may safely and more aggressively use executeMaybeImmediately, safe in the knowledge it will never permit cross-executor executions or multiple executor locks to be held. Also: - Rename PreLoadContext -> ExecutionContext - Break out AccordExecutor/AccordTask into separate package |
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| AGENTS.md | ||
| CASSANDRA-14092.txt | ||
| CHANGES.txt | ||
| CLAUDE.md | ||
| CONTRIBUTING.md | ||
| LICENSE.txt | ||
| NEWS.txt | ||
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| README.asc | ||
| SECURITY.md | ||
| TESTING.md | ||
| build-shaded-dtest-jar.sh | ||
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README.asc
image:https://img.shields.io/badge/License-Apache%202.0-blue.svg[License, link=https://github.com/apache/cassandra/blob/trunk/LICENSE.txt] image:https://ci-cassandra.apache.org/job/Cassandra-trunk/badge/icon[Build Status, link=https://ci-cassandra.apache.org/job/Cassandra-trunk/] image:https://img.shields.io/badge/Official-Downloads-brightgreen[Official Downloads, link=https://cassandra.apache.org/$$_$$/download.html] image:https://img.shields.io/docker/pulls/$$_$$/cassandra[Docker Pulls, link=https://hub.docker.com/r/$$_$$/cassandra] image:https://img.shields.io/badge/Slack-4A154B?style=flat&logo=slack&logoColor=white[Slack, link=https://infra.apache.org/slack.html] image:https://img.shields.io/badge/Bluesky-0285FF?logo=bluesky&logoColor=fff&color=0285FF[Bluesky, link=https://bsky.app/profile/cassandra.apache.org] image:https://img.shields.io/badge/-LinkedIn-blue?style=flat-square&logo=Linkedin&logoColor=white&link=https://www.linkedin.com/company/apache-cassandra/[LinkedIn, link=https://www.linkedin.com/company/apache-cassandra/] image:https://img.shields.io/badge/YouTube-FF0000?style=flat&logo=youtube&logoColor=white[Youtube, link=https://www.youtube.com/c/PlanetCassandra] Apache Cassandra ----------------- Apache Cassandra is a highly-scalable partitioned row store. Rows are organized into tables with a required primary key. https://cwiki.apache.org/confluence/display/CASSANDRA2/Partitioners[Partitioning] means that Cassandra can distribute your data across multiple machines in an application-transparent matter. Cassandra will automatically repartition as machines are added and removed from the cluster. https://cwiki.apache.org/confluence/display/CASSANDRA2/DataModel[Row store] means that like relational databases, Cassandra organizes data by rows and columns. The Cassandra Query Language (CQL) is a close relative of SQL. For more information, see https://cassandra.apache.org/[the Apache Cassandra web site]. Issues should be reported on https://issues.apache.org/jira/projects/CASSANDRA/issues/[The Cassandra Jira]. Requirements ------------ - Java: see supported versions in build.xml (search for property "java.supported"). - Python: for `cqlsh`, see `bin/cqlsh` (search for function "is_supported_version"). Getting started --------------- This short guide will walk you through getting a basic one node cluster up and running, and demonstrate some simple reads and writes. For a more-complete guide, please see the Apache Cassandra website's https://cassandra.apache.org/doc/latest/cassandra/getting-started/index.html[Getting Started Guide]. First, we'll unpack our archive: $ tar -zxvf apache-cassandra-$VERSION.tar.gz $ cd apache-cassandra-$VERSION After that we start the server. Running the startup script with the -f argument will cause Cassandra to remain in the foreground and log to standard out; it can be stopped with ctrl-C. $ bin/cassandra -f Now let's try to read and write some data using the Cassandra Query Language: $ bin/cqlsh The command line client is interactive so if everything worked you should be sitting in front of a prompt: ---- Connected to Test Cluster at localhost:9160. [cqlsh 6.3.0 | Cassandra 7.0-SNAPSHOT | CQL spec 3.4.8 | Native protocol v5] Use HELP for help. cqlsh> ---- As the banner says, you can use 'help;' or '?' to see what CQL has to offer, and 'quit;' or 'exit;' when you've had enough fun. But lets try something slightly more interesting: ---- cqlsh> CREATE KEYSPACE schema1 WITH replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 }; cqlsh> USE schema1; cqlsh:Schema1> CREATE TABLE users ( user_id varchar PRIMARY KEY, first varchar, last varchar, age int ); cqlsh:Schema1> INSERT INTO users (user_id, first, last, age) VALUES ('jsmith', 'John', 'Smith', 42); cqlsh:Schema1> SELECT * FROM users; user_id | age | first | last ---------+-----+-------+------- jsmith | 42 | john | smith cqlsh:Schema1> ---- If your session looks similar to what's above, congrats, your single node cluster is operational! For more on what commands are supported by CQL, see https://cassandra.apache.org/doc/trunk/cassandra/developing/cql/index.html[the CQL reference]. A reasonable way to think of it is as, "SQL minus joins and subqueries, plus collections." Wondering where to go from here? * Join us in #cassandra on the https://s.apache.org/slack-invite[ASF Slack] and ask questions. * Subscribe to the Users mailing list by sending a mail to user-subscribe@cassandra.apache.org. * Subscribe to the Developer mailing list by sending a mail to dev-subscribe@cassandra.apache.org. * Visit the https://cassandra.apache.org/community/[community section] of the Cassandra website for more information on getting involved. * Visit the https://cassandra.apache.org/doc/latest/development/index.html[development section] of the Cassandra website for more information on how to contribute.