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Andres de la Peña commented on CASSANDRA-15752: ----------------------------------------------- +1 > Range read concurrency factor didn't consider range merger > ---------------------------------------------------------- > > Key: CASSANDRA-15752 > URL: https://issues.apache.org/jira/browse/CASSANDRA-15752 > Project: Cassandra > Issue Type: Bug > Components: Legacy/Coordination > Reporter: ZhaoYang > Assignee: ZhaoYang > Priority: Normal > Fix For: 3.0.x, 3.11.x, 4.0-beta > > > During range read, coordinator computes concurrency factor which is the > number of vnode ranges to contact in parallel for the next batch. > But in {{RangeCommandIterator}}, vnode ranges are merged by {{RangeMerger}} > if vnode ranges share enough replicas to satisfy consistency level. eg. vnode > range [a,b) has replica n1,n2,n3 and vnode range [b,c) has replica n2,n3,n4, > so they can be merged as range [a,c) with replica n2, n3 for Quorum. > Currently it counts number of merged ranges towards concurrency factor. > Coordinator may fetch more ranges than needed. > ---- > Another issue is that when executing range read on table with very small > amount of data, concurrency factor can be bumped to {{size of total vnode > ranges}}, eg. 10k, depending on the num of vnodes and cluster size. As a > result, coordinator will send large number of concurrent range requests, > potentially slowing down the cluster.. We should cap the max concurrency > factor.. -- This message was sent by Atlassian Jira (v8.3.4#803005) --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org