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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11315) Keeping MVCC for configurable longer time
Date Wed, 02 Jul 2014 00:26:25 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11315?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14049460#comment-14049460

stack commented on HBASE-11315:

bq. Should we suggest to keep MVCC forever in dev list?

I suppose these will occupy space in the bc but in the scheme of things not much?  They occupy
space anyways since we have a placeholder in the KV/Cell class?  If so, could keep them forever.

Purging them means we take up less space in the fs but not in bc?  If so, I suppose if we
are looking at the keys at compaction time anyways, no harm letting them go either.

if the cost of keeping them in fs is small and we KNOW they are permanent, we might be able
to simplify in a few places and exploit this facility in others.  That'd be the argument for
keeping them forever.

> Keeping MVCC for configurable longer time 
> ------------------------------------------
>                 Key: HBASE-11315
>                 URL: https://issues.apache.org/jira/browse/HBASE-11315
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.99.0
>            Reporter: Jeffrey Zhong
>            Assignee: Jeffrey Zhong
>         Attachments: hbase-11315.patch
> After hbase-8763, we need keep mvcc number longer in hfile so that it can be used to
order changes during writes. For example, the known put,delete,put,... scenario, cross region
server scan, out of order puts(in recovery case).
> Current thinking is that we make the retention period configurable(below we're using
1 day to explain). During major compaction, we check hfile's creation time if a hfile creation
time is older than 1 day then all mvcc of KVs in that hfile will be removed. If a hfile is
created within 1 day, then all mvccs of KVs in that hfile will be kept. 
> In case there are time clock skew, we can firstly sort hfiles based on its seqId in ascending
order and find the first hfile's creation time stamp less than 1 day. Then mvcc of all hfiles
before the found file will be removed during compaction. 

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