I agree with Duo’s comment that a performance gain is unlikely but would be orthogonal anyway; 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.
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. > On Nov 15, 2020, at 5:20 AM, 张铎 <palomino...@gmail.com> wrote: > > Replied on jira, I think we missed an important scenario when testing. > > Thanks. > > Stack <st...@duboce.net> 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 >>
