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https://issues.apache.org/jira/browse/HDFS-15202?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17057937#comment-17057937
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Lisheng Sun commented on HDFS-15202:
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Thanx [~pustota] for your report.
I understand your PR is allocating more ShortCircuitCaches, to utilize each
ShortCircuitCache's own lock without blocking each othe to solve performance
problems.
Therefore, we need to consider distributing the blocks as evenly as possible in
more caches. The current code is simply taking the remainder through the
blockId and clientShortCircuitNum. This should also have hot cache issues.
Please correct me i was wrong. Thank you.
> HDFS-client: boost ShortCircuit Cache
> -------------------------------------
>
> Key: HDFS-15202
> URL: https://issues.apache.org/jira/browse/HDFS-15202
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: dfsclient
> Environment: 4 nodes E5-2698 v4 @ 2.20GHz, 700 Gb Mem.
> 8 RegionServers (2 by host)
> 8 tables by 64 regions by 1.88 Gb data in each = 900 Gb total
> Random read in 800 threads via YCSB and a little bit updates (10% of reads)
> Reporter: Danil Lipovoy
> Assignee: Danil Lipovoy
> Priority: Minor
> Attachments: HDFS_CPU_full_cycle.png, cpu_SSC.png, cpu_SSC2.png,
> hdfs_cpu.png, hdfs_reads.png, hdfs_scc_3_test.png,
> hdfs_scc_test_full-cycle.png, locks.png, requests_SSC.png
>
>
> ТотI want to propose how to improve reading performance HDFS-client. The
> idea: create few instances ShortCircuit caches instead of one.
> The key points:
> 1. Create array of caches (set by
> clientShortCircuitNum=*dfs.client.short.circuit.num*, see in the pull
> requests below):
> {code:java}
> private ClientContext(String name, DfsClientConf conf, Configuration config) {
> ...
> shortCircuitCache = new ShortCircuitCache[this.clientShortCircuitNum];
> for (int i = 0; i < this.clientShortCircuitNum; i++) {
> this.shortCircuitCache[i] = ShortCircuitCache.fromConf(scConf);
> }
> {code}
> 2 Then divide blocks by caches:
> {code:java}
> public ShortCircuitCache getShortCircuitCache(long idx) {
> return shortCircuitCache[(int) (idx % clientShortCircuitNum)];
> }
> {code}
> 3. And how to call it:
> {code:java}
> ShortCircuitCache cache =
> clientContext.getShortCircuitCache(block.getBlockId());
> {code}
> The last number of offset evenly distributed from 0 to 9 - that's why all
> caches will full approximately the same.
> It is good for performance. Below the attachment, it is load test reading
> HDFS via HBase where clientShortCircuitNum = 1 vs 3. We can see that
> performance grows ~30%, CPU usage about +15%.
> Hope it is interesting for someone.
> Ready to explain some unobvious things.
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