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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2294) Enumerate ACID properties of HBase in a well defined spec
Date Fri, 02 Apr 2010 04:12:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2294?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852694#action_12852694
] 

stack commented on HBASE-2294:
------------------------------

I read the spec. with the onlining of regions to take writes but not reads and I do not see
violation.  I did wonder though if we should have a section on what happens if you try to
read and system can't give you known correct data -- e.g. the exception thrown if you try
to read an onlined region that is replaying edits -- but thought this an implementation detail
that didn't belong herein.

> 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
>
>         Attachments: formatting_mods-v2.patch, formatting_mods.patch
>
>
> 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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