[jdbc] Add support for SQL:2008 FETCH FIRST n ROWS ONLY for Scans (#1373)

jdbc/src/main/java/site/ycsb/db/JdbcDBClient.java

@@ -82,7 +82,11 @@ public class JdbcDBClient extends DB {
   /** The field name prefix in the table. */
   public static final String COLUMN_PREFIX = "FIELD";
 
-  private boolean sqlserver = false;
+  /** SQL:2008 standard: FETCH FIRST n ROWS after the ORDER BY. */
+  private boolean sqlansiScans = false;
+  /** SQL Server before 2012: TOP n after the SELECT. */
+  private boolean sqlserverScans = false;
+
   private List<Connection> conns;
   private boolean initialized = false;
   private Properties props;
@@ -184,8 +188,6 @@ public class JdbcDBClient extends DB {
     String passwd = props.getProperty(CONNECTION_PASSWD, DEFAULT_PROP);
     String driver = props.getProperty(DRIVER_CLASS);
 
-  
-
     this.jdbcFetchSize = getIntProperty(props, JDBC_FETCH_SIZE);
     this.batchSize = getIntProperty(props, DB_BATCH_SIZE);
 
@@ -193,9 +195,23 @@ public class JdbcDBClient extends DB {
     this.batchUpdates = getBoolProperty(props, JDBC_BATCH_UPDATES, false);
 
     try {
+//  The SQL Syntax for Scan depends on the DB engine
+//  - SQL:2008 standard: FETCH FIRST n ROWS after the ORDER BY
+//  - SQL Server before 2012: TOP n after the SELECT
+//  - others (MySQL,MariaDB, PostgreSQL before 8.4)
+//  TODO: check product name and version rather than driver name
       if (driver != null) {
         if (driver.contains("sqlserver")) {
-          sqlserver = true;
+          sqlserverScans = true;
+          sqlansiScans = false;
+        }
+        if (driver.contains("oracle")) {
+          sqlserverScans = false;
+          sqlansiScans = true;
+        }
+        if (driver.contains("postgres")) {
+          sqlserverScans = false;
+          sqlansiScans = true;
         }
         Class.forName(driver);
       }
@@ -308,7 +324,7 @@ public class JdbcDBClient extends DB {
 
   private PreparedStatement createAndCacheScanStatement(StatementType scanType, String key)
       throws SQLException {
-    String select = dbFlavor.createScanStatement(scanType, key, sqlserver);
+    String select = dbFlavor.createScanStatement(scanType, key, sqlserverScans, sqlansiScans);
     PreparedStatement scanStatement = getShardConnectionByKey(key).prepareStatement(select);
     if (this.jdbcFetchSize > 0) {
       scanStatement.setFetchSize(this.jdbcFetchSize);
@@ -357,9 +373,11 @@ public class JdbcDBClient extends DB {
       if (scanStatement == null) {
         scanStatement = createAndCacheScanStatement(type, startKey);
       }
-      if (sqlserver) {
+      // SQL Server TOP syntax is at first
+      if (sqlserverScans) {
         scanStatement.setInt(1, recordcount);
         scanStatement.setString(2, startKey);
+      // FETCH FIRST and LIMIT are at the end
       } else {
         scanStatement.setString(1, startKey);
         scanStatement.setInt(2, recordcount);

jdbc/src/main/java/site/ycsb/db/flavors/DBFlavor.java

@@ -65,5 +65,6 @@ public abstract class DBFlavor {
   /**
    * Create and return a SQL statement for scanning data.
    */
-  public abstract String createScanStatement(StatementType scanType, String key, boolean sqlserver);
+  public abstract String createScanStatement(StatementType scanType, String key,
+                                             boolean sqlserverScans, boolean sqlansiScans);
 }

jdbc/src/main/java/site/ycsb/db/flavors/DefaultDBFlavor.java

@@ -84,9 +84,9 @@ public class DefaultDBFlavor extends DBFlavor {
   }
 
   @Override
-  public String createScanStatement(StatementType scanType, String key, boolean sqlserver) {
+  public String createScanStatement(StatementType scanType, String key, boolean sqlserverScans, boolean sqlansiScans) {
     StringBuilder select;
-    if (sqlserver) {
+    if (sqlserverScans) {
       select = new StringBuilder("SELECT TOP (?) * FROM ");
     } else {
       select = new StringBuilder("SELECT * FROM ");
@@ -97,8 +97,12 @@ public class DefaultDBFlavor extends DBFlavor {
     select.append(" >= ?");
     select.append(" ORDER BY ");
     select.append(JdbcDBClient.PRIMARY_KEY);
-    if (!sqlserver) {
-      select.append(" LIMIT ?");
+    if (!sqlserverScans) {
+      if (sqlansiScans) {
+        select.append(" FETCH FIRST ? ROWS ONLY");
+      } else {
+        select.append(" LIMIT ?");
+      }
     }
     return select.toString();
   }