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Lars Hofhansl commented on HBASE-10015: --------------------------------------- The 3x improvement I see for tall tables. For wider tables the improvement is less pronounced (for 5 columns I see a 20% or so improvement). Also a note as to why I think this should be correct: Even with the current synchronized, a next/peek/reseek that has already started, will finish with the old reader. That has not changed. Need to look closer at races between close() and next/peek/reseek, as close could be called from another thread (I think), when the lease expired. > Major performance improvement: Avoid synchronization in StoreScanner > -------------------------------------------------------------------- > > Key: HBASE-10015 > URL: https://issues.apache.org/jira/browse/HBASE-10015 > Project: HBase > Issue Type: Bug > Reporter: Lars Hofhansl > Attachments: 10015-0.94.txt > > > Did some more profiling (this time with a sampling profiler) and > StoreScanner.peek() showed up a lot in the samples. At first that was > surprising, but peek is synchronized, so it seems a lot of the sync'ing cost > is eaten there. > It seems the only reason we have to synchronize all these methods is because > a concurrent flush or compaction can change the scanner stack, other than > that only a single thread should access a StoreScanner at any given time. > So replaced updateReaders() with some code that just indicates to the scanner > that the readers should be updated and then make it the using thread's > responsibility to do the work. > The perf improvement from this is staggering. I am seeing somewhere around 3x > scan performance improvement across all scenarios. > Now, the hard part is to reason about whether this is 100% correct. I ran > TestAtomicOperation and TestAcidGuarantees a few times in a loop, all still > pass. > Will attach a sample patch. -- This message was sent by Atlassian JIRA (v6.1#6144)