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ramkrishna.s.vasudevan commented on HBASE-13082: ------------------------------------------------ [~lhofhansl] I agree to your point that reference counting is risky is some cases where there is no unified way of incrementing/decrementing. Is there a better way we can do it? Or shall we unify the way the store files scanners are accessed and closed? > Coarsen StoreScanner locks to RegionScanner > ------------------------------------------- > > Key: HBASE-13082 > URL: https://issues.apache.org/jira/browse/HBASE-13082 > Project: HBase > Issue Type: Bug > Components: Performance, Scanners > Reporter: Lars Hofhansl > Assignee: ramkrishna.s.vasudevan > Priority: Major > Fix For: 1.3.0, 2.0.0 > > Attachments: 13082-test.txt, 13082-v2.txt, 13082-v3.txt, > 13082-v4.txt, 13082.txt, 13082.txt, CountDownLatch-0.98.txt, HBASE-13082.pdf, > HBASE-13082_1.pdf, HBASE-13082_12.patch, HBASE-13082_13.patch, > HBASE-13082_14.patch, HBASE-13082_15.patch, HBASE-13082_16.patch, > HBASE-13082_17.patch, HBASE-13082_18.patch, HBASE-13082_19.patch, > HBASE-13082_1_WIP.patch, HBASE-13082_2.pdf, HBASE-13082_2_WIP.patch, > HBASE-13082_3.patch, HBASE-13082_4.patch, HBASE-13082_9.patch, > HBASE-13082_9.patch, HBASE-13082_withoutpatch.jpg, HBASE-13082_withpatch.jpg, > LockVsSynchronized.java, gc.png, gc.png, gc.png, hits.png, next.png, next.png > > > Continuing where HBASE-10015 left of. > We can avoid locking (and memory fencing) inside StoreScanner by deferring to > the lock already held by the RegionScanner. > In tests this shows quite a scan improvement and reduced CPU (the fences make > the cores wait for memory fetches). > There are some drawbacks too: > * All calls to RegionScanner need to be remain synchronized > * Implementors of coprocessors need to be diligent in following the locking > contract. For example Phoenix does not lock RegionScanner.nextRaw() and > required in the documentation (not picking on Phoenix, this one is my fault > as I told them it's OK) > * possible starving of flushes and compaction with heavy read load. > RegionScanner operations would keep getting the locks and the > flushes/compactions would not be able finalize the set of files. > I'll have a patch soon. -- This message was sent by Atlassian JIRA (v7.6.3#76005)