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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6980) Parallel Flushing Of Memstores
Date Wed, 17 Oct 2012 18:42:04 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6980?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13478212#comment-13478212

Todd Lipcon commented on HBASE-6980:

If I remember correctly, there is a reason for the flush marker: it ensures that the RS hasn't
been fenced on HDFS -- i.e that it hasn't lost its connection to ZK and already had its log
splitting started.

The reason this is important is that, otherwise, it could move on to delete old log segments,
which would potentially break the log split process.

It may be that the locking can be more lax, though.
> Parallel Flushing Of Memstores
> ------------------------------
>                 Key: HBASE-6980
>                 URL: https://issues.apache.org/jira/browse/HBASE-6980
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Kannan Muthukkaruppan
>            Assignee: Kannan Muthukkaruppan
> For write dominated workloads, single threaded memstore flushing is an unnecessary bottleneck.
With a single flusher thread, we are basically not setup to take advantage of the aggregate
throughput that multi-disk nodes provide.
> * For puts with WAL enabled, the bottleneck is more likely the "single" WAL per region
server. So this particular fix may not buy as much unless we unlock that bottleneck with multiple
commit logs per region server. (Topic for a separate JIRA-- HBASE-6981).
> * But for puts with WAL disabled (e.g., when using HBASE-5783 style fast bulk imports),
we should be able to support much better ingest rates with parallel flushing of memstores.

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