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https://issues.apache.org/jira/browse/ACCUMULO-1950?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eric Newton reassigned ACCUMULO-1950:
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Assignee: Eric Newton
> Reduce the number of calls to hsync
> ------------------------------------
>
> Key: ACCUMULO-1950
> URL: https://issues.apache.org/jira/browse/ACCUMULO-1950
> Project: Accumulo
> Issue Type: Improvement
> Reporter: Keith Turner
> Assignee: Eric Newton
> Fix For: 1.7.0
>
>
> As mutations written to a tablet server its buffered and once this buffer
> exceeds a certain size the data is dumped to the walog and then inserted into
> an in memory sorted map. These walog buffers are per a client and the max
> size is determined by tserver.mutation.queue.max.
> Accumulo 1.5 and 1.6 call hsync() in hadoop 2 which ensures data is flushed
> to disk. This introduces a fixed delay when flushing walog buffers. The
> smaller tserver.mutation.queue.max is, the more frequently the walog buffers
> are flushed. With many clients writing to a tserver, this is not much of a
> concern because all of their walog buffers are flushed using group commit.
> This results in high throughput because large batches of data being written
> before hsync is called. However if a few client writing to a tserver there
> will be a lot more calls to hsync. It would be nice the # of calls to hsync
> was a function of the amount of data written regardless of the number of
> concurrent clients. Currently as the number of concurrent clients goes down,
> the number of calls to hsync goes up.
> In 1.6 and 1.5 this can be mitigated by increasing
> tserver.mutation.queue.max, however this is multiplied by the number of
> concurrent writers. So increasing it can improve performance of a single
> writer but increases the chances of many concurrent writers exhausting memory.
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