Sequence of logs: Before logs: 2020-07-29 11:33:00:736*[ERROR]*transformconvertreg (1/2)*RequestHandler*onFailure*Unexpected error while querying nosqldb-0.nosqldb.default.svc.cluster.local/host2 com.datastax.driver.core.exceptions.ConnectionException: [nosqldb-0.nosqldb.default.svc.cluster.local/host2:9042] Pool is CLOSING at com.datastax.driver.core.HostConnectionPool.borrowConnection(HostConnectionPool.java:241) at com.datastax.driver.core.RequestHandler$SpeculativeExecution.query(RequestHandler.java:397) at com.datastax.driver.core.RequestHandler$SpeculativeExecution.findNextHostAndQuery(RequestHandler.java:360) --------------------------------------------------------------------------------------------- Posted log in datastax community.. 2020-07-29 11:33:00:747*[ERROR]*transformconvertreg (2/2)*RequestHandler*onFailure*Unexpected error while querying nosqldb-2.nosqldb.default.svc.cluster.local/host1 com.datastax.driver.core.exceptions.ConnectionException: [nosqldb-2.nosqldb.default.svc.cluster.local/host1:9042] Pool is CLOSING at com.datastax.driver.core.HostConnectionPool.borrowConnection(HostConnectionPool.java:241) at com.datastax.driver.core.RequestHandler$SpeculativeExecution.query(RequestHandler.java:397) at com.datastax.driver.core.RequestHandler$SpeculativeExecution.findNextHostAndQuery(RequestHandler.java:360) ---------------------------------------------------------------------------------------------- after logs: 2020-07-29 11:33:00:771*[ERROR]*transformconvertreg (2/2)*RegistrationRecordConvertor*processElement java.lang.RuntimeException: Error preparing queries for accessor DetailsAccessor at com.datastax.driver.mapping.AccessorMapper.prepare(AccessorMapper.java:63) at com.datastax.driver.mapping.MappingManager.getAccessor(MappingManager.java:359) at com.datastax.driver.mapping.MappingManager.createAccessor(MappingManager.java:321) at com.test.cassandra.dao.DetailsDao.fetchDetailsImpl(DetailsDao.java:87) at com.test.cloud.util.DAOUtils.fetchDetails(DAOUtils.java:130) at com.test.cloud.processing.operators.RegistrationRecordConvertor.processElement(RegistrationRecordConvertor.java:94) at com.test.cloud.processing.operators.RegistrationRecordConvertor.processElement(RegistrationRecordConvertor.java:45) at org.apache.flink.streaming.api.operators.KeyedProcessOperator.processElement(KeyedProcessOperator.java:85) at org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:202) at org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:105) at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:300) at org.apache.flink.runtime.taskmanager.Task.run(Task.java:711) at java.lang.Thread.run(Thread.java:748) Caused by: java.util.concurrent.ExecutionException: com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query failed (tried: nosqldb-2.nosqldb.default.svc.cluster.local/host1:9042 (com.datastax.driver.core.exceptions.ConnectionException: [nosqldb-2.nosqldb.default.svc.cluster.local/host1:9042] Pool is CLOSING)) at com.google.common.util.concurrent.AbstractFuture.getDoneValue(AbstractFuture.java:502) at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:461) at com.google.common.util.concurrent.AbstractFuture$TrustedFuture.get(AbstractFuture.java:83) at com.datastax.driver.mapping.AccessorMapper.prepare(AccessorMapper.java:58) ... 12 common frames omitted Caused by: com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query failed (tried: nosqldb-2.nosqldb.default.svc.cluster.local/host1:9042 (com.datastax.driver.core.exceptions.ConnectionException: [nosqldb-2.nosqldb.default.svc.cluster.local/host1:9042] Pool is CLOSING)) 2020-07-29 11:33:00:783*[ERROR]*transformconvertreg (2/2)*RegistrationRecordConvertor*processElement java.lang.RuntimeException: Error preparing queries for accessor DetailsAccessor at com.datastax.driver.mapping.AccessorMapper.prepare(AccessorMapper.java:63) at com.datastax.driver.mapping.MappingManager.getAccessor(MappingManager.java:359) at com.datastax.driver.mapping.MappingManager.createAccessor(MappingManager.java:321) at com.test.cassandra.dao.DetailsDao.fetchDetailsImpl(DetailsDao.java:87) at com.test.cloud.util.DAOUtils.fetchDetails(DAOUtils.java:130)