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https://issues.apache.org/jira/browse/HBASE-17910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15975963#comment-15975963
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stack commented on HBASE-17910:
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bq. I found a problem that when opening an HFileReader, we will read a lot of
data such as trailer, index, and so on.
This stuff is not in cache ? Maybe not the trailer but the index... Could we
add trailer etc. to cache to save on these reads?
> Use separated StoreFileReader for streaming read
> ------------------------------------------------
>
> Key: HBASE-17910
> URL: https://issues.apache.org/jira/browse/HBASE-17910
> Project: HBase
> Issue Type: Improvement
> Reporter: Duo Zhang
>
> For now we have already supportted using private readers for compaction, by
> creating a new StoreFile copy. I think a better way is to allow creating
> multiple readers from a single StoreFile instance, thus we can avoid the ugly
> cloning, and the reader can also be used for streaming scan, not only for
> compaction.
> The reason we want to do this is that, we found a read amplification when
> using short circult read. {{BlockReaderLocal}} will use an internal buffer to
> read data first, the buffer size is based on the configured buffer size and
> the readahead option in CachingStrategy. For normal pread request, we should
> just bypass the buffer, this can be achieved by setting readahead to 0. But
> for streaming read I think the buffer is somehow still useful? So we need to
> use different FSDataInputStream for pread and streaming read.
> And one more thing is that, we can also remove the streamLock if streaming
> read always use its own reader.
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