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RE: [EXTERNAL] Writes and Reads with high latency

Can you provide the schema and the queries? What is the RF of the keyspace for the data? Are you using any Retry policy on your Cluster object?



Sean Durity


From: Marco Gasparini <marco.gasparini@xxxxxxxxxxxxxxx>
Sent: Friday, December 21, 2018 10:45 AM
To: user@xxxxxxxxxxxxxxxxxxxx
Subject: [EXTERNAL] Writes and Reads with high latency


hello all,


I have 1 DC of 3 nodes in which is running Cassandra 3.11.3 with consistency level ONE and Java 1.8.0_191.


Every day, there are many nodejs programs that send data to the cassandra's cluster via NodeJs cassandra-driver.

Every day I got like 600k requests. Each request makes the server to:

1_ READ some data in Cassandra (by an id, usually I get 3 records),

2_ DELETE one of those records

3_ WRITE the data into Cassandra.


So every day I make many deletes.


Every day I find errors like:

"All host(s) tried for query failed. First host tried, Host considered as DOWN. See innerErrors...."

"Server timeout during write query at consistency LOCAL_ONE (0 peer(s) acknowledged the write over 1 required)...."

"Server timeout during write query at consistency SERIAL (0 peer(s) acknowledged the write over 1 required)...."

"Server timeout during read query at consistency LOCAL_ONE (0 peer(s) acknowledged the read over 1 required)...."


nodetool tablehistograms tells me this:


Percentile  SSTables     Write Latency      Read Latency    Partition Size        Cell Count

                              (micros)          (micros)           (bytes)

50%             8.00            379.02           1955.67            379022                 8

75%            10.00            785.94         155469.30            654949                17

95%            12.00          17436.92         268650.95           1629722                35

98%            12.00          25109.16         322381.14           2346799                42

99%            12.00          30130.99         386857.37           3379391                50

Min             0.00              6.87             88.15               104                 0

Max            12.00          43388.63         386857.37          20924300               179


in the 99% I noted that write and read latency is pretty high, but I don't know how to improve that.

I can provide more statistics if needed.


Is there any improvement I can make to the Cassandra's configuration in order to not to lose any data?






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