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https://issues.apache.org/jira/browse/HDDS-16983?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chu Cheng Li reassigned HDDS-16983:
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Assignee: Chu Cheng Li
> Reuse chunk streams for positioned reads in BlockInputStream
> ------------------------------------------------------------
>
> Key: HDDS-16983
> URL: https://issues.apache.org/jira/browse/HDDS-16983
> Project: Apache Ozone
> Issue Type: Improvement
> Components: Ozone Client
> Reporter: Chu Cheng Li
> Assignee: Chu Cheng Li
> Priority: Major
> Labels: pull-request-available
>
> h3. Background
> HDDS-16396 added concurrent positioned reads to {{BlockInputStream}}. A
> positioned read does not change the stream position or the buffers of
> sequential reads.
> h3. Problem
> For each positioned read, {{BlockInputStream}} creates a new
> {{ChunkInputStream}} for each chunk that the read covers. It closes this
> stream after the read. But the block already has one {{ChunkInputStream}} for
> each chunk. Thus, each positioned read creates objects that the block already
> has.
> The new stream is necessary today because {{ChunkInputStream.readPositioned}}
> writes the shared {{datanodeBlockID}} field. A shared stream cannot do this
> write safely during concurrent reads.
> h3. Changes
> * Move the range logic of {{ChunkInputStream}} to a new class,
> {{ChunkReader}}. This logic aligns a range to the checksum boundaries and
> copies the requested bytes. {{ChunkReader}} keeps no position and no data
> buffers.
> * Positioned reads use the existing chunk streams of the block. They do not
> create a new stream for each read.
> * A positioned read builds the {{DatanodeBlockID}} as a local value. It does
> not write the shared field.
> * Each positioned read still gets its own client from
> {{XceiverClientFactory}} and releases it after the read. Short-circuit reads
> still read the local block file.
> * When a positioned read fails, it refreshes the pipeline. It does not
> release the clients of the sequential chunk streams.
> h3. Tests
> * Concurrent positioned reads from a local block file. The test checks that
> the file position and the stream position do not change.
> * Two {{ChunkReader}} reads at the same time. The test checks that the reads
> do not block each other and do not change the source buffers.
> HDDS-16325 tracks the larger refactor of the {{BlockInputStream}} state.
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