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From srinivasarao daruna <>
Subject Impact of Write without consistency level and mutation failures on reads and cluster
Date Fri, 16 Jun 2017 02:10:52 GMT

Recently one of our spark job had missed cassandra consistency property and
number of concurrent writes property.

Due to that, some of mutations are failed when we checked tpstats. Also, we
observed readtimeouts are occurring with not only the table that the job
inserts, but also from other tables, for which have always had consistency
level proper. We started repair, but due to the volume of data, repair
might take a day or two to complete. Mean while, wanted to get some inputs.

As the error planted lot of questions.
1) Is there a relation between mutation fails to read time outs and overall
cluster performance, if yes, how.?

2) When i checked the log, i found a warning in debug.log as below.
SELECT * FROM our_table WHERE partition_key = required_value LIMIT 5000:
total time 20353 msec - timeout 20000 msec

Actual query:
SELECT * FROM our_table WHERE partition_key = required_value

Even though we are hitting partition key, i do not understand the reason
for such huge read time and timeouts.

3) We are using prepared statements to query the tables from API. How can
we set the fetch size, so that it wont use LIMIT 5000.?
Any thoughts.?

Thank You,

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