Connection error handling fixups (#433)

Fixes a connection error exception handler case.

- [x] Add some backoff logic to the reconnection attempts.

Author: bpkroth

src/main/java/com/oltpbenchmark/api/Worker.java

@@ -30,6 +30,7 @@
 import java.sql.SQLException;
 import java.sql.SQLRecoverableException;
 import java.sql.Statement;
+import java.time.Duration;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -400,7 +401,17 @@ protected final void doWork(DatabaseType databaseType, TransactionType transacti
         if (this.conn == null) {
           try {
             if (!this.configuration.getNewConnectionPerTxn()) {
-              LOG.info("(Re)connecting to database.");
+              if (retryCount > 0) {
+                Duration delay = Duration.ofSeconds(Math.min(retryCount, 5));
+                LOG.info("Backing off {} seconds before reconnecting.", delay.toSeconds());
+                try {
+                  Thread.sleep(delay);
+                } catch (InterruptedException ex) {
+                  // pass
+                }
+              } else {
+                LOG.info("(Re)connecting to database.");
+              }
             }
             this.conn = this.benchmark.makeConnection();
             this.conn.setAutoCommit(false);
@@ -598,6 +609,8 @@ protected final void doWork(DatabaseType databaseType, TransactionType transacti
             } catch (SQLException e) {
               LOG.error("Connection couldn't be closed.", e);
             }
+          } else if (this.conn == null) {
+            LOG.warn("Connection error detected.");
           }
 
           switch (status) {

src/main/java/com/oltpbenchmark/util/SQLUtil.java

@@ -715,7 +715,7 @@ public static boolean isConnectionErrorException(SQLException ex) {
         || ex.getMessage().endsWith("connection was unexpectedly lost.")
         || ex.getMessage().endsWith("Command could not be timed out. Reason: Socket closed")
         || ex.getMessage().endsWith("No operations allowed after connection closed")
-        || ex.getMessage().endsWith("Communications link failure")) {
+        || ex.getMessage().contains("Communications link failure")) {
       return true;
     }