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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1364) [performance] Distributed splitting of regionserver commit logs
Date Wed, 24 Mar 2010 06:59:28 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12849082#action_12849082
] 

stack commented on HBASE-1364:
------------------------------

I was thinking that we could use a coprocessor to do log sort/split.  One thing that needs
addressing is that each Store in a Region reads the whole log itself.  Seems like reading
of the old edits should be done once at region level (I don't think this would be hard to
do).  Other things, in BT paper, they talk of regions asking for edits after they come back
online.   First, the region is already online again before log split starts -- maybe its already
taking on writes?  -- and second, somehow the region knew what logs they want to get edits
from (Recheck paper. I'm pulling from rusty memory).

> [performance] Distributed splitting of regionserver commit logs
> ---------------------------------------------------------------
>
>                 Key: HBASE-1364
>                 URL: https://issues.apache.org/jira/browse/HBASE-1364
>             Project: Hadoop HBase
>          Issue Type: Improvement
>            Reporter: stack
>            Priority: Critical
>             Fix For: 0.21.0
>
>
> HBASE-1008 has some improvements to our log splitting on regionserver crash; but it needs
to run even faster.
> (Below is from HBASE-1008)
> In bigtable paper, the split is distributed. If we're going to have 1000 logs, we need
to distribute or at least multithread the splitting.
> 1. As is, regions starting up expect to find one reconstruction log only. Need to make
it so pick up a bunch of edit logs and it should be fine that logs are elsewhere in hdfs in
an output directory written by all split participants whether multithreaded or a mapreduce-like
distributed process (Lets write our distributed sort first as a MR so we learn whats involved;
distributed sort, as much as possible should use MR framework pieces). On startup, regions
go to this directory and pick up the files written by split participants deleting and clearing
the dir when all have been read in. Making it so can take multiple logs for input, can also
make the split process more robust rather than current tenuous process which loses all edits
if it doesn't make it to the end without error.
> 2. Each column family rereads the reconstruction log to find its edits. Need to fix that.
Split can sort the edits by column family so store only reads its edits.

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