So what is your purpose of distributing the request of region location lookup? It is just because you want to 'distribute the request of region location lookup'?
Then I'm -1 on merging. We should reach an agreement on what we want to solve before merging at least. I've helped this issue from the design doc step. For me, the purpose for this issue is clear. We want to prevent the hotspot of meta, so the solution is simple, enable meta replica, and then just modify the client to not always go to primary replica first(this is the old behavior even with meta replica feature on). And this will introduce another problem that, there is no meta region replication implementation for meta read replicas, which means the latency will be large as we can only sync the data between replicas through region flush, so we implement meta region replication. So I think it is very important to verify that we have truly distributed the request of region location lookup, and also make sure that we could support more requests of region location lookup. Otherwise this feature is useless. And I agree with Andrew that, since the feature is default off on branch-2 and has no regression, it is OK to merge for now. Theoretically our approach here should work, so even it does not work for now, I think we could fix the problems to make it work. But your reply above made me wonder whether we are talking about the same thing. That's why I'm -1 here. I'm not going to force you to do the test suggested by me, as I said it could be done after merging, just want to reach an agreement on the goal of this feature. Thanks. Stack <[email protected]> 于2020年11月16日周一 下午12:35写道： > On Sun, Nov 15, 2020 at 9:16 AM Andrew Purtell <[email protected]> > wrote: > > > I agree with Duo’s comment that a performance gain is unlikely but would > > be orthogonal anyway; > > > Perf observation is just an aside in the issue. Perf is orthogonal as you > say above (as long as no regression). > > > > > it’s an availability gain that is the goal. We can assume it based on > > theory of operation and unit test results but the gain should be tested > and > > measured on a cluster too. > > > > > The feature is about distributing load on hbase:meta to alleviate > hotspotting; it makes read replicas more live so replicas are more likely > to satisfy location lookups making read replicas more effective. That read > replicas improve HA is presumed -- it was the original justification for > this years old commit -- but HA is not the focus of this addition; hence no > reports on effectiveness in this area. > > I have no problem working on such tests/reports but suggest that they are > done post merge. > > > > > That said, the results of the testing thus far indicate no regression, > > which gives me confidence to support a merge. Specifically, a merge to > > “unblock” 2.4 (we aren’t really blocked, we are waiting), provided the > > default there is the feature is configured off. But please indicate in > > documentation and release notes that the feature is not widely tested > yet - > > as is customarily done for new functionality like this. > > > > > No problem w/ flagging the feature as new. > > Thanks, > S > > > > > > > > On Nov 15, 2020, at 5:20 AM, 张铎 <[email protected]> wrote: > > > > > > Replied on jira, I think we missed an important scenario when testing. > > > > > > Thanks. > > > > > > Stack <[email protected]> 于2020年11月15日周日 上午2:30写道： > > > > > >> HBASE-18070 makes it so hbase:meta read replicas can run closer to the > > >> primary, (< second lags rather than minutes). It adds Async WAL > > >> Replication[1] on the hbase:meta table; i.e. edits are sprayed across > > >> replicas as they arrive at the primary's WAL. Before this work, Async > > WAL > > >> Replication was only available on user-space tables and the only > option > > for > > >> hbase:meta read replicas was reloading the primaries hfiles on a > period > > >> (minutes). HBASE-18070 also adds an optional client-side 'LoadBalance' > > >> policy that favors read replicas ahead of primary reads falling back > to > > the > > >> primary on fault. Together, these additions allow distributing > > hbase:meta > > >> read load across primary and replicas alleviating 'hotspotting'. > > >> > > >> I would like to merge the feature to master branch Monday evening if > > there > > >> is no objection (Soon after I'll merge to branch-2 so this feature can > > >> hopefully be included in the upcoming 2.4.0RC). > > >> > > >> * For the design, see [2]. > > >> * For an amalgamated PR of the 5 or 6 reviewed PRs that comprise this > > >> feature, see [3]. > > >> * For a PE report that compared performance before and after, see > > >> HBASE-25127 (no regression). > > >> * A report on ITBLL runs is pending to be attached to HBASE-18070 but > > runs > > >> so far show no regression with the feature enabled (ITBLL runs were > done > > >> against a backport of this feature to branch-2 as the ITBLL state of > > master > > >> is currently an unknown). > > >> > > >> Testing continues mainly looking for further improvement and to better > > >> understand this feature in operation. Documentation is included but in > > need > > >> of polish (working on it). > > >> > > >> Dump any questions here and I'll be happy to respond. If you need more > > time > > >> to review, just shout. > > >> > > >> Thanks and thanks to all who contributed to this feature; the > reviewers > > and > > >> the testers in particular. > > >> > > >> S > > >> > > >> 1. http://hbase.apache.org/book.html#_asnyc_wal_replication > > >> 2. > > >> > > >> > > > https://docs.google.com/document/d/1jJWVc-idHhhgL4KDRpjMsQJKCl_NRaCLGiH3Wqwd3O8/edit# > > >> This patch is currently missing HBASE-25280, a bug found in testing. > > >> 3. https://github.com/apache/hbase/pull/2643 > > >> > > >
