diff --git a/core/src/main/java/com/scalar/db/storage/cassandra/BatchHandler.java b/core/src/main/java/com/scalar/db/storage/cassandra/BatchHandler.java
index b604e5bf4..36662b7bb 100644
--- a/core/src/main/java/com/scalar/db/storage/cassandra/BatchHandler.java
+++ b/core/src/main/java/com/scalar/db/storage/cassandra/BatchHandler.java
@@ -73,7 +73,6 @@ public void handle(List<? extends Mutation> mutations)
             CoreError.CASSANDRA_OPERATION_FAILED_IN_BATCH.buildMessage(writeType), e);
       }
     } catch (RuntimeException e) {
-      logger.warn(e.getMessage(), e);
       throw new RetriableExecutionException(
           CoreError.CASSANDRA_ERROR_OCCURRED_IN_BATCH.buildMessage(e.getMessage()), e);
     }
diff --git a/core/src/main/java/com/scalar/db/storage/cassandra/MutateStatementHandler.java b/core/src/main/java/com/scalar/db/storage/cassandra/MutateStatementHandler.java
index a5d99a2c7..2594da421 100644
--- a/core/src/main/java/com/scalar/db/storage/cassandra/MutateStatementHandler.java
+++ b/core/src/main/java/com/scalar/db/storage/cassandra/MutateStatementHandler.java
@@ -15,14 +15,10 @@
 import com.scalar.db.exception.storage.RetriableExecutionException;
 import javax.annotation.Nonnull;
 import javax.annotation.concurrent.ThreadSafe;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /** An abstraction for handler classes for mutate statements */
 @ThreadSafe
 public abstract class MutateStatementHandler extends StatementHandler {
-  private static final Logger logger = LoggerFactory.getLogger(MutateStatementHandler.class);
-
   public MutateStatementHandler(Session session) {
     super(session);
   }
@@ -48,7 +44,6 @@ public ResultSet handle(Operation operation) throws ExecutionException {
       }
       return results;
     } catch (WriteTimeoutException e) {
-      logger.warn("Write timeout happened during mutate operation", e);
       if (e.getWriteType() == WriteType.CAS) {
         // retry needs to be done if applications need to do the operation exactly
         throw new RetriableExecutionException(
@@ -71,7 +66,6 @@ public ResultSet handle(Operation operation) throws ExecutionException {
             CoreError.CASSANDRA_WRITE_TIMEOUT_WITH_OTHER_WRITE_TYPE_IN_MUTATION.buildMessage(), e);
       }
     } catch (RuntimeException e) {
-      logger.warn(e.getMessage(), e);
       throw new RetriableExecutionException(
           CoreError.CASSANDRA_ERROR_OCCURRED_IN_MUTATION.buildMessage(e.getMessage()), e);
     }
diff --git a/core/src/main/java/com/scalar/db/storage/cassandra/SelectStatementHandler.java b/core/src/main/java/com/scalar/db/storage/cassandra/SelectStatementHandler.java
index 4d6b335b6..2cb476087 100644
--- a/core/src/main/java/com/scalar/db/storage/cassandra/SelectStatementHandler.java
+++ b/core/src/main/java/com/scalar/db/storage/cassandra/SelectStatementHandler.java
@@ -33,8 +33,6 @@
 import java.util.stream.IntStream;
 import javax.annotation.Nonnull;
 import javax.annotation.concurrent.ThreadSafe;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
  * A handler class for select statement
@@ -43,8 +41,6 @@
  */
 @ThreadSafe
 public class SelectStatementHandler extends StatementHandler {
-  private static final Logger logger = LoggerFactory.getLogger(SelectStatementHandler.class);
-
   /**
    * Constructs {@code SelectStatementHandler} with the specified {@code Session}
    *
@@ -60,7 +56,6 @@ public ResultSet handle(Operation operation) throws ExecutionException {
     try {
       return handleInternal(operation);
     } catch (RuntimeException e) {
-      logger.error(e.getMessage(), e);
       throw new ExecutionException(
           CoreError.CASSANDRA_ERROR_OCCURRED_IN_SELECTION.buildMessage(e.getMessage()), e);
     }
@@ -294,8 +289,7 @@ private Ordering getOrdering(Scan.Ordering ordering) {
       case DESC:
         return QueryBuilder.desc(quoteIfNecessary(ordering.getColumnName()));
       default:
-        logger.warn("Unsupported ordering specified. Using Order.ASC");
-        return QueryBuilder.asc(quoteIfNecessary(ordering.getColumnName()));
+        throw new AssertionError("Unsupported ordering is specified: " + ordering.getOrder());
     }
   }
 
diff --git a/core/src/main/java/com/scalar/db/storage/cassandra/StatementHandler.java b/core/src/main/java/com/scalar/db/storage/cassandra/StatementHandler.java
index e2b5fe286..980ca796f 100644
--- a/core/src/main/java/com/scalar/db/storage/cassandra/StatementHandler.java
+++ b/core/src/main/java/com/scalar/db/storage/cassandra/StatementHandler.java
@@ -14,13 +14,10 @@
 import com.scalar.db.exception.storage.ExecutionException;
 import javax.annotation.Nonnull;
 import javax.annotation.concurrent.ThreadSafe;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /** A handler class for statements */
 @ThreadSafe
 public abstract class StatementHandler {
-  private static final Logger logger = LoggerFactory.getLogger(StatementHandler.class);
   protected final Session session;
   protected final StatementCache cache;
 
@@ -119,8 +116,7 @@ public static ConsistencyLevel convert(Operation operation, Consistency consiste
           return ConsistencyLevel.QUORUM;
         }
       default:
-        logger.warn("Unsupported consistency is specified. SEQUENTIAL is being used instead");
-        return ConsistencyLevel.QUORUM;
+        throw new AssertionError("Unsupported consistency is specified: " + consistency);
     }
   }
 
diff --git a/core/src/main/java/com/scalar/db/storage/cosmos/BatchHandler.java b/core/src/main/java/com/scalar/db/storage/cosmos/BatchHandler.java
index 498129765..b72733b95 100644
--- a/core/src/main/java/com/scalar/db/storage/cosmos/BatchHandler.java
+++ b/core/src/main/java/com/scalar/db/storage/cosmos/BatchHandler.java
@@ -12,8 +12,6 @@
 import java.util.ArrayList;
 import java.util.List;
 import javax.annotation.concurrent.ThreadSafe;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
  * A handler for a batch
@@ -22,7 +20,6 @@
  */
 @ThreadSafe
 public class BatchHandler {
-  private static final Logger logger = LoggerFactory.getLogger(BatchHandler.class);
   private static final String MUTATION_STORED_PROCEDURE = "mutate.js";
   private final CosmosClient client;
   private final TableMetadataManager metadataManager;
@@ -88,7 +85,6 @@ private void executeStoredProcedure(
   }
 
   private void throwException(CosmosException exception) throws ExecutionException {
-    logger.error(exception.getMessage(), exception);
     int statusCode = exception.getSubStatusCode();
 
     if (statusCode == CosmosErrorCode.PRECONDITION_FAILED.get()) {
diff --git a/core/src/main/java/com/scalar/db/storage/cosmos/MutateStatementHandler.java b/core/src/main/java/com/scalar/db/storage/cosmos/MutateStatementHandler.java
index d0956687a..0cf7c9170 100644
--- a/core/src/main/java/com/scalar/db/storage/cosmos/MutateStatementHandler.java
+++ b/core/src/main/java/com/scalar/db/storage/cosmos/MutateStatementHandler.java
@@ -12,13 +12,10 @@
 import java.util.ArrayList;
 import java.util.List;
 import javax.annotation.concurrent.ThreadSafe;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /** An abstraction for handler classes for mutate statements */
 @ThreadSafe
 public abstract class MutateStatementHandler extends StatementHandler {
-  private static final Logger logger = LoggerFactory.getLogger(MutateStatementHandler.class);
   private static final String MUTATION_STORED_PROCEDURE = "mutate.js";
 
   public MutateStatementHandler(CosmosClient client, TableMetadataManager metadataManager) {
@@ -60,7 +57,6 @@ protected void executeStoredProcedure(Mutation mutation, TableMetadata tableMeta
   }
 
   private void throwException(CosmosException exception) throws ExecutionException {
-    logger.error(exception.getMessage());
     int statusCode = exception.getSubStatusCode();
 
     if (statusCode == CosmosErrorCode.PRECONDITION_FAILED.get()) {