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https://issues.apache.org/jira/browse/HADOOP-19641?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Anuj Modi updated HADOOP-19641:
-------------------------------
Description:
We have observed this across multiple workload runs that when we start reading
data from input stream. The first read which came to input stream has to be
read synchronously even if we trigger prefetch request for that particular
offset. Most of the times we end up doing extra work of checking if the
prefetch is trigerred, removing prefetch from the pending queue and go ahead to
do a direct remote read in workload thread itself.
To avoid all this overhead, we will always bypass read ahead for the very first
read of each input stream and trigger read aheads for second read onwards.
> ABFS: [ReadAheadV2] First Read should bypass ReadBufferManager
> --------------------------------------------------------------
>
> Key: HADOOP-19641
> URL: https://issues.apache.org/jira/browse/HADOOP-19641
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/azure
> Affects Versions: 3.4.1
> Reporter: Anuj Modi
> Assignee: Anuj Modi
> Priority: Major
> Labels: Performance
>
> We have observed this across multiple workload runs that when we start
> reading data from input stream. The first read which came to input stream has
> to be read synchronously even if we trigger prefetch request for that
> particular offset. Most of the times we end up doing extra work of checking
> if the prefetch is trigerred, removing prefetch from the pending queue and go
> ahead to do a direct remote read in workload thread itself.
> To avoid all this overhead, we will always bypass read ahead for the very
> first read of each input stream and trigger read aheads for second read
> onwards.
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