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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2294) Enumerate ACID properties of HBase in a well defined spec
Date Fri, 02 Apr 2010 00:39:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2294?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852622#action_12852622
] 

Todd Lipcon commented on HBASE-2294:
------------------------------------

Yep, I think that makes sense. Do you think anything in this document precludes that? Basically
what we're discussing here is cleverness that allows us to be more useful while maintaining
the same guarantees. So long as our "spec" (output of this JIRA) talks about user visible
properties, we can feel free to be as clever as we want underneath :)

> Enumerate ACID properties of HBase in a well defined spec
> ---------------------------------------------------------
>
>                 Key: HBASE-2294
>                 URL: https://issues.apache.org/jira/browse/HBASE-2294
>             Project: Hadoop HBase
>          Issue Type: Task
>          Components: documentation
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Blocker
>             Fix For: 0.20.4, 0.21.0
>
>
> It's not written down anywhere what the guarantees are for each operation in HBase with
regard to the various ACID properties. I think the developers know the answers to these questions,
but we need a clear spec for people building systems on top of HBase. Here are a few sample
questions we should endeavor to answer:
> - For a multicell put within a CF, is the update made durable atomically?
> - For a put across CFs, is the update made durable atomically?
> - Can a read see a row that hasn't been sync()ed to the HLog?
> - What isolation do scanners have? Somewhere between snapshot isolation and no isolation?
> - After a client receives a "success" for a write operation, is that operation guaranteed
to be visible to all other clients?
> etc
> I see this JIRA as having several points of discussion:
> - Evaluation of what the current state of affairs is
> - Evaluate whether we currently provide any guarantees that aren't useful to users of
the system (perhaps we can drop in exchange for performance)
> - Evaluate whether we are missing any guarantees that would be useful to users of the
system

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