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Sean Comerford commented on CASSANDRA-9753: ------------------------------------------- We also hit this adding a new DC - our LOCAL_ONE reads against datacenter X were sometimes getting sent to datacenter Y as soon as it joined the cluster and had even partial data for the partition requested. Adjusting the dc_local_read_repair_chance to be 0.0 fixed the issue for us. > LOCAL_QUORUM reads can block cross-DC if there is a digest mismatch > ------------------------------------------------------------------- > > Key: CASSANDRA-9753 > URL: https://issues.apache.org/jira/browse/CASSANDRA-9753 > Project: Cassandra > Issue Type: Bug > Components: Legacy/Coordination > Reporter: Richard Low > Priority: Normal > > When there is a digest mismatch during the initial read, a data read request > is sent to all replicas involved in the initial read. This can be more than > the initial blockFor if read repair was done and if speculative retry kicked > in. E.g. for RF 3 in two DCs, the number of reads could be 4: 2 for > LOCAL_QUORUM, 1 for read repair and 1 for speculative read if one replica was > slow. If there is then a digest mismatch, Cassandra will issue the data read > to all 4 and set blockFor=4. Now the read query is blocked on cross-DC > latency. The digest mismatch read blockFor should be capped at RF for the > local DC when using CL.LOCAL_*. > You can reproduce this behaviour by creating a keyspace with > NetworkTopologyStrategy, RF 3 per DC, dc_local_read_repair=1.0 and ALWAYS for > speculative read. If you force a digest mismatch (e.g. by deleting a replicas > SSTables and restarting) you can see in tracing that it is blocking for 4 > responses. -- 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