[jira] [Resolved] (HDFS-15202) HDFS-client: boost ShortCircuit Cache

["Wei-Chiu Chuang (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-15202?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wei-Chiu Chuang resolved HDFS-15202.
------------------------------------
    Fix Version/s: 3.4.0
       Resolution: Fixed

> 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
>             Fix For: 3.4.0
>
>         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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