Chu Cheng Li created HDDS-17399:
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Summary: Make positioned reads lock-free after initialization in
BlockInputStream and StreamBlockInputStream
Key: HDDS-17399
URL: https://issues.apache.org/jira/browse/HDDS-17399
Project: Apache Ozone
Issue Type: Improvement
Components: Ozone Client
Reporter: Chu Cheng Li
Assignee: Chu Cheng Li
h3. Problem
* {{BlockInputStream.readPositioned}} and
{{StreamBlockInputStream.readPositioned}} take the stream lock on each call.
* The sequential read of each class keeps the same lock while it waits for the
datanode.
* Thus a positioned read waits for a sequential read in progress on the same
block.
h3. Changes
After the one-time setup of a block stream, a positioned read takes no lock.
* {{BlockInputStream}}: after the volatile {{initialized}} is true, read
{{chunkOffsets}}, {{chunkStreams}} and {{length}} without the lock.
{{initialize()}} sets them first, and nothing changes them after that.
* {{StreamBlockInputStream}}: make {{needUpdateBlockLength}} volatile, and call
{{updateBlockLength()}} only while it is set. Make {{xceiverClientFactory}}
final.
* The block streams do not check that they are open. {{MultipartInputStream}},
their only caller, checks its volatile {{closed}} flag first.
* Sequential reads do not change.
h3. Tests
* For both classes, a positioned read completes while a sequential read on the
same block holds the lock. Without the change, it times out.
* After {{close()}}, a positioned read fails and does not reach the block
stream.
h3. Benchmark
One host, 3 datanodes, warm page cache. One shared stream on a 256 MiB key: 1
sequential reader and N positioned-read threads. Median of 3 runs.
||Read path||Positioned reads||Before (ops/s, p50, p99)||After (ops/s, p50,
p99)||
|Chunk (default)|1 thread x 64 KiB|2, 680 ms, 1.55 s|1,811, 0.41 ms, 1.36 ms|
|Chunk (default)|8 threads x 64 KiB|9, 721 ms, 4.89 s|7,398, 0.78 ms, 2.04 ms|
|Stream ({{ozone.client.stream.readblock.enable}})|1 thread x 64 KiB|3, 309 ms,
641 ms|586, 1.3 ms, 5.6 ms|
|Stream ({{ozone.client.stream.readblock.enable}})|8 threads x 64 KiB|10, 653
ms, 3.56 s|2,060, 3.3 ms, 9.4 ms|
* With positioned reads only (1 to 32 threads), throughput does not change
beyond run-to-run noise (about ±10%).
Follow-up to HDDS-16983 and HDDS-16395.
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