Yup. Verified again that this table is being written, read, and replicated to just one data center.
________________________________ From: Naik, Ninad Sent: Monday, October 15, 2018 1:18:43 PM To: user@cassandra.apache.org Subject: Re: Cassandra: Inconsistent data on reads (LOCAL_QUORUM) Let me double check that. ________________________________ From: Jeff Jirsa <jji...@gmail.com> Sent: Monday, October 15, 2018 11:49:10 AM To: user@cassandra.apache.org Subject: Re: Cassandra: Inconsistent data on reads (LOCAL_QUORUM) [ This email has been sent from a source external to Epsilon. Please use caution when clicking links or opening attachments. ] Are you SURE there are no writes to that table coming from another DC? -- Jeff Jirsa On Oct 15, 2018, at 5:34 PM, Naik, Ninad <ninad.n...@epsilon.com<mailto:ninad.n...@epsilon.com>> wrote: Thanks Jeff. We're not doing deletes, but I will take a look at this jira. ________________________________ From: Jeff Jirsa <jji...@gmail.com<mailto:jji...@gmail.com>> Sent: Sunday, October 14, 2018 12:55:17 PM To: user@cassandra.apache.org<mailto:user@cassandra.apache.org> Subject: Re: Cassandra: Inconsistent data on reads (LOCAL_QUORUM) [ This email has been sent from a source external to Epsilon. Please use caution when clicking links or opening attachments. ] If this is 2.1 AND you do deletes AND you have a non-zero number of failed writes (timeouts), it’s possibly short reads 3.0 fixes this ( https://issues.apache.org/jira/browse/CASSANDRA-12872 ), it won’t be backported to 2.1 because it’s a significant change to how reads are executed -- Jeff Jirsa On Oct 13, 2018, at 7:24 PM, Naik, Ninad <ninad.n...@epsilon.com<mailto:ninad.n...@epsilon.com>> wrote: Thanks Maitrayee. I should have mentioned this as one of the things we verified. The clocks on cassandra nodes are in sync. ________________________________ From: maitrayee shah <koolja...@yahoo.com.INVALID<mailto:koolja...@yahoo.com.INVALID>> Sent: Friday, October 12, 2018 6:40:25 PM To: user@cassandra.apache.org<mailto:user@cassandra.apache.org> Subject: Re: Cassandra: Inconsistent data on reads (LOCAL_QUORUM) [ This email has been sent from a source external to Epsilon. Please use caution when clicking links or opening attachments. ] We have seen inconsistent read if the clock on the nodes are not in sync. Thank you Sent from my iPhone On Oct 12, 2018, at 1:50 PM, Naik, Ninad <ninad.n...@epsilon.com<mailto:ninad.n...@epsilon.com>> wrote: Hello, We're seeing inconsistent data while doing reads on cassandra. Here are the details: It's is a wide column table. The columns can be added my multiple machines, and read by multiple machines. The time between writes and reads are in minutes, but sometimes can be in seconds. Writes happen every 2 minutes. Now, while reading we're seeing the following cases of inconsistent reads: * One column was added. If a read was done after the column was added (20 secs to 2 minutes after the write), Cassandra returns no data. As if the key doesn't exist. If the application retries, it gets the data. * A few columns exist for a row key. And a new column 'n' was added. Again, a read happens a few minutes after the write. This time, only the latest column 'n' is returned. In this case the app doesn't know that the data is incomplete so it doesn't retry. If we manually retry, we see all the columns. * A few columns exist for a row key. And a new column 'n' is added. When a read happens after the write, all columns but 'n' are returned. Here's what we've verified: * Both writes and reads are using 'LOCAL_QUORUM' consistency level. * The replication is within local data center. No remote data center is involved in the read or write. * During the inconsistent reads, none of the nodes are undergoing GC pauses * There are no errors in cassandra logs * Reads always happen after the writes. A few other details: Cassandra version: 2.1.9 DataStax java driver version: 2.1.10.2 Replication Factor: 3 We don't see this problem in lower environments. We have seen this happen once or twice last year, but since last few days it's happening quite frequently. On an average 2 inconsistent reads every minute. Here's how the table definition looks like: CREATE TABLE "MY_TABLE" ( key text, sub_key text, value text, PRIMARY KEY ((key), sub_key) ) WITH bloom_filter_fp_chance=0.010000 AND caching='{"keys":"ALL", "rows_per_partition":"NONE"}' AND comment='' AND dclocal_read_repair_chance=0.100000 AND gc_grace_seconds=864000 AND read_repair_chance=0.000000 AND default_time_to_live=0 AND speculative_retry='ALWAYS' AND memtable_flush_period_in_ms=0 AND compaction={'class': 'SizeTieredCompactionStrategy'} AND compression={'sstable_compression': 'LZ4Compressor'}; Please point us in the right direction. Thanks ! The information contained in this e-mail message and any attachments may be privileged and confidential. If the reader of this message is not the intended recipient or an agent responsible for delivering it to the intended recipient, you are hereby notified that any review, dissemination, distribution or copying of this communication is strictly prohibited. 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