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