maoling edited a comment on issue #1098: ZOOKEEPER-3560: Add response cache to serve get children (2) requests. URL: https://github.com/apache/zookeeper/pull/1098#issuecomment-544462596 - Look at the original design from ZOOKEEPER-3180, it wants to put the serialization of response into the cache to save the cost of serialization of read operation. - My confusion is: this optimization is only appiled to the big znode(> 1MB), it should be enable by default? - I also see the description mentions this optimization will ease GC's overhead - serialization is a cpu-cost operation? Putting more thing into the cache(memory) will hava more likely to trigger the full GC(STW)? - I also doubt about: adding this cache will bring about some issues about read inconsistency? but if client is FIFO, it may not a problem. - I also do a benchmark for this feature:my env:8Core,16G,256SSD; standalone mode;1000 znodes operationcount=1000(all is read).thread count=1 ``` Test for small znode: data length:100 -Dzookeeper.maxGetChildrenResponseCacheSize=-1 -Dzookeeper.maxResponseCacheSize=-1 Sample 5 times:Throughput(ops/sec): (778.21 + 954.19 + 1019.36 + 974.65 + 1209.18)/5=987.11 -Dzookeeper.maxGetChildrenResponseCacheSize=1000 -Dzookeeper.maxResponseCacheSize=1000 cache_hits_rate:5012.0/（5012 + 989.0)= 83% Sample 5 times:Throughput(ops/sec): (794.91 + 833.33 + 953.28 + 812.34 + 591.36)/5=797.04 ------------------------------------------------------------------------ Test for big znode: data length:10000 -Dzookeeper.maxGetChildrenResponseCacheSize=-1 -Dzookeeper.maxResponseCacheSize=-1 (704.72 + 475.05 + 900.90 + 736.91 + 836.82)/5=730.88 -Dzookeeper.maxGetChildrenResponseCacheSize=1000 -Dzookeeper.maxResponseCacheSize=1000 cache_hits_rate:4012.0/(4012.0+988.0)=80% (508.13 + 891.26 + 811.03 + 901.71 + 985.22)/5=819.47 ------------------------------------------------------------------------ Test for big znode: data length:100000 -Dzookeeper.maxGetChildrenResponseCacheSize=-1 -Dzookeeper.maxResponseCacheSize=-1 (299.94 + 339.21 + 318.67 + 261.98 + 364.29)/5=316.81 -Dzookeeper.maxGetChildrenResponseCacheSize=1000 -Dzookeeper.maxResponseCacheSize=1000 cache_hits_rate: 4021/（4021+979)=80% (349.77 + 332.66 + 386.39 + 392.92 + 343.76)/5=361.1 ``` My observation is: enable this feature will have a performance degradation for small znode. For big znode have slight performance improvement(almost 15%), not notable as expected.
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