查询大Oracle数据库表的CLOB和LONG时,出现性能问题。如何提高Oracle-DB中的CLOB和LONG值的查询性能(cx_Oracle vs OJDBC)?
到目前为止,我写了下面的单元测试与cx_Oracle(蟒蛇)和JDBC(Java):
Python代码使用cx_Oracle:使用ojdbc7.jar
class CXOraclePerformanceTest(TestCase):
def test_cx_oracle_performance_with_clob(self):
self.execute_cx_oracle_performance("CREATE TABLE my_table (my_text CLOB)")
def test_cx_oracle_performance_with_long(self):
self.execute_cx_oracle_performance("CREATE TABLE my_table (my_text LONG)")
def execute_cx_oracle_performance(self, create_table_statement):
# prepare test data
current_milli_time = lambda: int(round(time.time() * 1000))
db = cx_Oracle.connect(CONNECT_STRING)
db.cursor().execute(create_table_statement)
db.cursor().execute("INSERT INTO my_table (my_text) VALUES ('abc')")
for i in range(13):
db.cursor().execute("INSERT INTO my_table (my_text) SELECT 'abc' FROM my_table")
row_count = db.cursor().execute("SELECT count(*) FROM my_table").fetchall()[0][0]
self.assertEqual(8192, row_count)
# execute query with big result set
timer = current_milli_time()
rows = db.cursor().execute("SELECT * FROM my_table")
for row in rows:
self.assertEqual("abc", str(row[0]))
timer = current_milli_time() - timer
print("{} -> duration: {} ms".format(create_table_statement, timer))
# clean-up
db.cursor().execute("DROP TABLE my_table")
db.close()
Java代码:
public class OJDBCPerformanceTest {
@Test public void testOJDBCPerformanceWithCLob() throws Exception {
testOJDBCPerformance("CREATE TABLE my_table (my_text CLOB)");
}
@Test public void testOJDBCPerformanceWithLong() throws Exception {
testOJDBCPerformance("CREATE TABLE my_table (my_text LONG)");
}
private void testOJDBCPerformance(String createTableStmt) throws Exception {
// prepare connection
OracleConnection connection = (OracleConnection) DriverManager.getConnection(connectionString);
connection.setAutoCommit(false);
connection.setDefaultRowPrefetch(512);
// prepare test data
Statement stmt = connection.createStatement();
stmt.execute(createTableStmt);
stmt.execute("INSERT INTO my_table (my_text) VALUES ('abc')");
for (int i = 0; i < 13; i++)
stmt.execute("INSERT INTO my_table (my_text) SELECT 'abc' FROM my_table");
ResultSet resultSet = stmt.executeQuery("SELECT count(*) FROM my_table");
resultSet.next();
Assert.assertEquals(8192, resultSet.getInt(1));
// execute query with big result set
long timer = new Date().getTime();
stmt = connection.createStatement();
resultSet = stmt.executeQuery("SELECT * FROM my_table");
while (resultSet.next())
Assert.assertEquals("abc", resultSet.getString(1));
timer = new Date().getTime() - timer;
System.out.println(String.format("%s -> duration: %d ms", createTableStmt, timer));
// clean-up
stmt = connection.createStatement();
stmt.execute("DROP TABLE my_table");
}
}
Python的测试输出:
CREATE TABLE my_table (my_text CLOB) -> duration: 31186 ms
CREATE TABLE my_table (my_text LONG) -> duration: 218 ms
Java测试输出:
CREATE TABLE my_table (my_text CLOB) -> duration: 359 ms
CREATE TABLE my_table (my_text LONG) -> duration: 14174 ms
- 为什么既是持续时间如此之高的区别?
- 如何改善一个或两个程序的性能?
- 是否有任何Oracle特定的选项或参数可用于提高查询性能?