[jira] [Updated] (HDDS-4651) Implement Distributed Sequence ID Generator

["Glen Geng (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDDS-4651?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Glen Geng updated HDDS-4651:
----------------------------
    Description: 
 
 * SCM allocates ids in a batch way. It maintains three fields: firstId, lastId and nextId. It saves the lastId in rocksDB, saves firstId and lastId in memory. The initial value of nextId is firstId.
 * When getNextId() is called, if nextId is less than lastId, SCM just returns nextId and increases it, otherwise it calls allocateBatch(expectedLastId, newLastId) to allocate a batch of ids, then serves the request.
 * In allocateBatch(expectedLastId, newLastId) , it works in CAS way:
 * it reads lastId from rocksDB.
 * if lastId equals expectedLastId, it saves newLastId into rocksDB, returns success, otherwise it rejects the allocation request.
 * It also provides a getLastId() to read lastId from rocksDB. The allocation works in a loop way:

  was:
/**
 * SequenceIDGenerator uses higher 30 bits to save the term, and lower 34 bits
 * to save a count (increase from 0). Each call of nextID() will increase the
 * count on the lower 34 bits by 1, thus SequenceIDGenerator always generates
 * unique number within a specific term.
 */


> Implement Distributed Sequence ID Generator 
> --------------------------------------------
>
>                 Key: HDDS-4651
>                 URL: https://issues.apache.org/jira/browse/HDDS-4651
>             Project: Apache Ozone
>          Issue Type: Sub-task
>            Reporter: Rui Wang
>            Assignee: Rui Wang
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.1.0
>
>
>  
>  * SCM allocates ids in a batch way. It maintains three fields: firstId, lastId and nextId. It saves the lastId in rocksDB, saves firstId and lastId in memory. The initial value of nextId is firstId.
>  * When getNextId() is called, if nextId is less than lastId, SCM just returns nextId and increases it, otherwise it calls allocateBatch(expectedLastId, newLastId) to allocate a batch of ids, then serves the request.
>  * In allocateBatch(expectedLastId, newLastId) , it works in CAS way:
>  * it reads lastId from rocksDB.
>  * if lastId equals expectedLastId, it saves newLastId into rocksDB, returns success, otherwise it rejects the allocation request.
>  * It also provides a getLastId() to read lastId from rocksDB. The allocation works in a loop way:



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