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reading","robots_txt_status":"success","robots_txt_updated_at":"2025-07-24T06:49:26.215Z","robots_txt_url":"https://github.com/robots.txt","online":false,"can_crawl_api":true,"host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["cassandra","consensus","java"],"created_at":"2026-01-11T18:01:22.049Z","updated_at":"2026-01-11T18:01:25.305Z","avatar_url":"https://github.com/datanerds-io.png","language":"Java","funding_links":[],"categories":[],"sub_categories":[],"readme":"[![Build Status](https://api.travis-ci.org/datanerds-io/lack.svg?branch=develop)](https://travis-ci.org/datanerds-io/lack)\n\n[![Maven Central](https://img.shields.io/maven-central/v/io.datanerds/lack.svg)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22io.datanerds%22%20a%3A%22lack%22)\n\nIn late 2014 DataStax published a [blog post](http://www.datastax.com/dev/blog/consensus-on-cassandra) in which they explain how Cassandra can be leveraged in order to reach consensus in a distributed environment. A detailed explanation can be found in mentioned article. In essence, a distributed lock or mutex mechanism to enforce that only one resource in a distributed and concurrent environment can be changed at the same time. Inspired by said article _LACK [luhk]_ was implemented. It is a very thin Java API on top of a few Cassandra queries. It is not meant as a consensus library such as libraft or atomix. We just needed something implemented fast and on top of Cassandra.\n\n# How to use it\n\n## Creating a keyspace\nIn order to run LACK you have to point it to a keyspace in which it can create necessary table.\n```sql\nCREATE KEYSPACE lack\n    WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };\n```\n## Locking\nYou can import LACK from Maven Central Repository:\n```xml\n\u003cdependency\u003e\n    \u003cgroupId\u003eio.datanerds\u003c/groupId\u003e\n    \u003cartifactId\u003elack\u003c/artifactId\u003e\n    \u003cversion\u003e0.1.1\u003c/version\u003e\n\u003c/dependency\u003e\n```\nThe configuration of LACK is done via the `LackConfig` POJO, e.g. using this constructor: `LackConfig(String username, String password, String[] nodes, String keyspace, int ttlInSeconds)`.\n\nConnecting to a a local cluster using the previously created keyspace and a TTL of 42 seconds:\n```java\nLackConfig config = new LackConfig(\"user\", \"pass\", new String[]{\"127.0.0.1\"}, \"lack\", 42);\nLack lack = new Lack(config, \"owner-1\");\n\n// Locking the resource:\nlack.acquire(\"user-1\");\n...\n// Renewing the lock in case we need longer than 42 seconds:\nlack.renew(\"user-1\");\n...\n// Claiming the lock results in renewal in case we're already owning it and acquiring otherwise\nlack.claim(\"user-1\");\n...\n// Releasing the lock in case we have finished our operation:\nlack.release(\"user-1\");\n```\n\nIn case one of the above mentioned methods can not be executed since e.g. a resource might already be locked, a `LackException` will be thrown. To make sure you implement a logic for such cases, it is a checked exception.\n\n# Build\n\nA `gradle build` will build the project. The test will start an embedded cassandra server. If the used ports are already in use the tests will fail.\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdatanerds-io%2Flack","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fdatanerds-io%2Flack","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fdatanerds-io%2Flack/lists"}