[20250125]如何编译与运行FetchSize.java.txt

[20250125]如何编译与运行FetchSize.java.txt --//https://connor-mcdonald.com/2025/01/17/jdbc-the-fetchsize-and-staying-up-to-date/ --//看了里面的链接，测试看看。 $ cat FetchSize.java import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class FetchSize {   public static void main(String[] args) throws SQLException {      try (Connection con = DriverManager.getConnection("jdbc:oracle:thin:scott/book@//127.0.0.1/book01p")) {     //   try (Connection con = DriverManager.getConnection("jdbc:oracle:thin:MYUSER/MYPASS@//MYHOST/MYDB?defaultRowPrefetch=1000")) {       try (Statement stmt = con.createStatement()) {         System.out.println("Creating test table");         try {           stmt.execute("drop table tmp_fetch_demo purge");         }         catch (SQLException ignored) {         }         stmt.execute("create table tmp_fetch_demo as select a.* from all_objects a, ( select 1 from dual connect by level <= 10) "); //        stmt.execute(""" //            create table tmp_fetch_demo as //            select a.* //              from all_objects a, (select 1 from dual connect by level <= 50)""");         System.out.println("Done."); // If you want to trace this // //        stmt.execute("alter session set tracefile_identifier = FETCH"); //        stmt.execute("alter session set sql_trace = true");         int newFetchSize;         if (args.length > 0 && (newFetchSize = Integer.parseInt(args[0])) > 0) {           System.out.println("Setting JDBC Statement default fetch size to " + newFetchSize);           stmt.setFetchSize(newFetchSize);         }         else if (stmt.getFetchSize() == 10) {           System.out.println("Keeping default JDBC Statement default fetch size (" + stmt.getFetchSize() + ")");         }         else {           System.out.println("JDBC Statement default fetch size set to " + stmt.getFetchSize() + " using connection string parameter");         }         try (ResultSet rs = stmt.executeQuery("select object_id, object_name from tmp_fetch_demo")) {           System.out.println("Querying all rows");           long startTime = System.nanoTime();           long cnt = 0;           while (rs.next()) {             int v1 = rs.getInt(1);             String v2 = rs.getString(2);             cnt++;           }           System.out.println("ResultSet fetch size " + rs.getFetchSize());           long duration = (System.nanoTime() - startTime) / 1000000L;           long tp = (long) ((double) cnt / duration * 1000d);           System.out.printf("Rows fetched %d%nDuration %d ms%nThroughput %d rows/sec%n", cnt, duration, tp);         }       }     }   } } --//已经根据要求修改连接数据库的字符串。仅仅减少select 1 from dual connect by level <= 10，不然建立的表有点大。 --//这样建立的表为120M。 $ javac FetchSize.java --//编译通过。 $ java FetchSize 0 Error: Could not find or load main class FetchSize $ java FetchSize 100 Error: Could not find or load main class FetchSize --//不熟悉java，视乎提示找不到对应的class FetchSize。 $ java -cp . FetchSize 100 Exception in thread "main" java.sql.SQLException: No suitable driver found for jdbc:oracle:thin:scott/book@//127.0.0.1/book01p         at java.sql.DriverManager.getConnection(DriverManager.java:689)         at java.sql.DriverManager.getConnection(DriverManager.java:270)         at FetchSize.main(FetchSize.java:9) --//jdbc没有找到。 $ java -cp /u01/app/oracle/product/21.0.0/dbhome_1/jdbc/lib/ojdbc8.jar:. FetchSize 100 Creating test table Done. Setting JDBC Statement default fetch size to 100 Querying all rows ResultSet fetch size 100 Rows fetched 699150 Duration 1066 ms Throughput 655863 rows/sec $ java -cp /u01/app/oracle/product/21.0.0/dbhome_1/jdbc/lib/ojdbc8.jar:. FetchSize 0 Creating test table Done. Keeping default JDBC Statement default fetch size (10) Querying all rows ResultSet fetch size 10 Rows fetched 699150 Duration 3471 ms Throughput 201426 rows/sec $ java -cp /u01/app/oracle/product/21.0.0/dbhome_1/jdbc/lib/ojdbc8.jar:. FetchSize Creating test table Done. Keeping default JDBC Statement default fetch size (10) Querying all rows ResultSet fetch size 10 Rows fetched 699150 Duration 3563 ms Throughput 196225 rows/sec --//设置0的缺省等于10。两者时间相差3倍。 --//不加参数如何执行,不是很清楚,那位知道。 --//应该设置某个环境变量就可以执行，不熟悉java。