我已经发布了一个相关问题，但我在这里提出更多细节问题：
我使用hibernate和以下代码从我的应用程序执行SQL查询：
Query query = session.getNamedQuery("sql.namedquery.captureinfo");
Long t0 = System.currentTimeMillis();
List<Object[]> sqlList = query.list();
Long t1 = System.currentTimeMillis();
System.err.println("SQL query took" + (t1 - t0));
处理此查询的时间大约是6秒。我使用H2作为底层数据库。 命名查询定义如下：
<sql-query name="sql.namedquery.captureinfo">
<return-scalar column="eoid" type="int"/>
<return-scalar column="oid" type="int"/>
<return-scalar column="capture.obs_sys_id" type="int"/>
<return-scalar column="capture.obs_mys_id" type="int"/>
<return-scalar column="mid" type="int"/>
<return-scalar column="hdwr.type_hdwr" type="string"/>
<return-scalar column="element_capture.description" type="string"/>
<return-scalar column="element_capture.dataf" type="string"/>
<return-scalar column="geometrie.point" type="materialized_blob"/>
<return-scalar column="geometrie.polygon" type="materialized_blob"/>
<return-scalar column="element_capture.date_min" type="date"/>
<return-scalar column="gid" type="int"/>
<return-scalar column="hdwr.nom" type="string"/>
select eo.id as eoid,o.id as oid,o.obs_sys_id,o.obs_mys_id,m.id as mid,m.type_hdwr,eo.description,eo.dataf,g.point,g.polygon,eo.date_min,g.id as gid,m.nom from element_capture eo left outer join geometrie g on eo.eo_geometrie_id = g.id left outer join hdwr m on eo.eo_hdwr_id = m.id left outer join capture o on eo.eo_capture_id = o.id
</sql-query>
使用H2的嵌入式SQL客户端执行完全相同的查询，它在不到一秒的时间内执行。 我还测试了直接使用JDBC来检查开销是否是由JDBC驱动程序引起的。这是代码：
package test;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class JDBCTest
{
public static void main(String[] args) throws ClassNotFoundException, SQLException
{
Class.forName("org.h2.Driver");
Connection connection = DriverManager.getConnection("jdbc:h2:data/mydatabase", "XXX", "YYY");
Long start = System.currentTimeMillis();
String request =
"select eo.id as eoid,o.id as oid,o.obs_sys_id,o.obs_mys_id,m.id as mid,m.type_hdwr,eo.description,eo.dataf,g.point,g.polygon,eo.date_min,g.id as gid,m.nom from element_capture eo left outer join geometrie g on eo.eo_geometrie_id = g.id left outer join hdwr m on eo.eo_hdwr_id = m.id left outer join capture o on eo.eo_capture_id = o.id";
PreparedStatement statement = connection.prepareStatement(request);
ResultSet res = statement.executeQuery();
while(res.next())
{
System.out.println(res.getInt(1) + "|" + res.getInt(2) + "|" + res.getInt(3) + "|" + res.getInt(4) + "|"
+ res.getInt(5) + "|" + res.getString(6) + "|" + res.getString(7) + "|" + res.getString(8) + "|"
+ res.getDate(11) + "|" + res.getInt(12) + "|" + res.getString(13));
Blob a = res.getBlob(9);
Blob b = res.getBlob(10);
a.getBytes(0, (int)a.length()); // make sure to stream out the blob
//b.getBytes(0, (int)b.length()); // commented out as b is null in every record
}
Long end = System.currentTimeMillis();
System.out.println((end - start) + "ms");
res.close();
statement.close();
connection.close();
}
}
执行此代码也需要大约一秒钟（包括在控制台中打印出结果，从数据库中检索到6398条记录）。
因此，同一查询的hibernate和JDBC版本之间存在相当大的开销，我不明白。我预计会有轻微的开销，但不是那么多。 我启用了详细的hibernate日志记录，这是日志的开头：
11:42:49,083 TRACE QueryPlanCache:200 - Located native-sql query plan in cache (select eo.id as eoid,o.id as oid,o.obs_sys_id,o.obs_mys_id,m.id as mid,m.type_hdwr,eo.description,eo.dataf,g.point,g.polygon,eo.date_min,g.id as gid,m.nom from element_capture eo left outer join geometrie g on eo.eo_geometrie_id = g.id left outer join hdwr m on eo.eo_hdwr_id = m.id left outer join capture o on eo.eo_capture_id = o.id)
11:42:49,112 TRACE ConnectionProxyHandler:110 - Handling invocation of connection method [prepareStatement]
11:42:49,113 DEBUG LogicalConnectionImpl:295 - Obtaining JDBC connection
11:42:49,115 TRACE DriverManagerConnectionProviderImpl:171 - Total checked-out connections: 1
11:42:49,116 DEBUG DriverManagerConnectionProviderImpl:192 - Opening new JDBC connection
11:42:49,121 DEBUG DriverManagerConnectionProviderImpl:202 - Created connection to: jdbc:h2:data/mydatabase, Isolation Level: 2
11:42:49,122 DEBUG LogicalConnectionImpl:301 - Obtained JDBC connection
11:42:49,142 DEBUG SQL:104 - select eo.id as eoid,o.id as oid,o.obs_sys_id,o.obs_mys_id,m.id as mid,m.type_hdwr,eo.description,eo.dataf,g.point,g.polygon,eo.date_min,g.id as gid,m.nom from element_capture eo left outer join geometrie g on eo.eo_geometrie_id = g.id left outer join hdwr m on eo.eo_hdwr_id = m.id left outer join capture o on eo.eo_capture_id = o.id
11:42:49,144 TRACE JdbcResourceRegistryImpl:65 - Registering statement [org.hibernate.engine.jdbc.internal.proxy.PreparedStatementProxyHandler@bf831db[valid=true]]
11:42:49,146 TRACE JdbcResourceRegistryImpl:75 - Registering last query statement [org.hibernate.engine.jdbc.internal.proxy.PreparedStatementProxyHandler@bf831db[valid=true]]
11:42:49,146 TRACE AbstractStatementProxyHandler:88 - Handling invocation of statement method [getWrappedObject]
11:42:49,147 TRACE JdbcResourceRegistryImpl:75 - Registering last query statement [prep3: select eo.id as eoid,o.id as oid,o.obs_sys_id,o.obs_mys_id,m.id as mid,m.type_hdwr,eo.description,eo.dataf,g.point,g.polygon,eo.date_min,g.id as gid,m.nom from element_capture eo left outer join geometrie g on eo.eo_geometrie_id = g.id left outer join hdwr m on eo.eo_hdwr_id = m.id left outer join capture o on eo.eo_capture_id = o.id]
11:42:49,148 TRACE Loader:1798 - Bound [1] parameters total
11:42:49,148 TRACE AbstractStatementProxyHandler:88 - Handling invocation of statement method [executeQuery]
11:42:53,537 TRACE JdbcResourceRegistryImpl:118 - Registering result set [org.hibernate.engine.jdbc.internal.proxy.ResultSetProxyHandler@42ea7f9f[valid=true]]
11:42:53,538 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getStatement]
11:42:53,540 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getStatement]
11:42:53,540 TRACE Loader:870 - Processing result set
11:42:53,541 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [next]
11:42:53,542 DEBUG Loader:873 - Result set row: 0
11:42:53,544 DEBUG Loader:1377 - Result row:
11:42:53,545 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,549 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,550 TRACE BasicExtractor:72 - Found [-6398] as column [eoid]
11:42:53,551 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,552 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,553 TRACE BasicExtractor:72 - Found [-6398] as column [oid]
11:42:53,554 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,555 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,556 TRACE BasicExtractor:72 - Found [-14] as column [capture.obs_sys_id]
11:42:53,557 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,558 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,558 TRACE BasicExtractor:72 - Found [13] as column [capture.obs_mys_id]
11:42:53,559 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,560 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,560 TRACE BasicExtractor:72 - Found [1] as column [mid]
11:42:53,561 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,562 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,562 TRACE BasicExtractor:72 - Found [APN] as column [hdwr.type_hdwr]
11:42:53,563 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,564 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,564 TRACE BasicExtractor:72 - Found [obsstatus=NON_VU;meta.filename=tap_1387464655536.zip] as column [element_capture.description]
11:42:53,565 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,565 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,566 TRACE BasicExtractor:72 - Found [tap_1387464655536.jpg] as column [element_capture.dataf]
11:42:53,567 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getBlob]
11:42:53,590 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,591 TRACE BasicExtractor:72 - Found [[B@2dce2a8d] as column [geometrie.point]
11:42:53,592 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getBlob]
11:42:53,593 TRACE BasicExtractor:67 - Found [null] as column [geometrie.polygon]
11:42:53,596 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getDate]
11:42:53,598 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,599 TRACE BasicExtractor:72 - Found [2013-12-19] as column [element_capture.date_min]
11:42:53,600 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,602 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,603 TRACE BasicExtractor:72 - Found [-6412] as column [gid]
11:42:53,604 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,605 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,606 TRACE BasicExtractor:72 - Found [TQ9GY] as column [hdwr.nom]
11:42:53,608 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [next]
11:42:53,609 DEBUG Loader:873 - Result set row: 1
11:42:53,610 DEBUG Loader:1377 - Result row:
11:42:53,611 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,612 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,613 TRACE BasicExtractor:72 - Found [-6397] as column [eoid]
11:42:53,614 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,619 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,620 TRACE BasicExtractor:72 - Found [-6397] as column [oid]
11:42:53,621 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,623 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,624 TRACE BasicExtractor:72 - Found [-14] as column [capture.obs_sys_id]
11:42:53,625 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,626 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,627 TRACE BasicExtractor:72 - Found [13] as column [capture.obs_mys_id]
11:42:53,628 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,629 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,630 TRACE BasicExtractor:72 - Found [1] as column [mid]
11:42:53,631 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,632 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,633 TRACE BasicExtractor:72 - Found [APN] as column [hdwr.type_hdwr]
11:42:53,634 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,634 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,635 TRACE BasicExtractor:72 - Found [obsstatus=A_REVOIR;meta.filename=tap_1387464653290.zip] as column [element_capture.description]
11:42:53,636 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,636 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,637 TRACE BasicExtractor:72 - Found [tap_1387464653290.jpg] as column [element_capture.dataf]
11:42:53,637 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getBlob]
11:42:53,639 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,639 TRACE BasicExtractor:72 - Found [[B@3f46a7e8] as column [geometrie.point]
11:42:53,640 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getBlob]
11:42:53,641 TRACE BasicExtractor:67 - Found [null] as column [geometrie.polygon]
11:42:53,642 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getDate]
11:42:53,644 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,645 TRACE BasicExtractor:72 - Found [2013-12-19] as column [element_capture.date_min]
11:42:53,646 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getInt]
11:42:53,647 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,647 TRACE BasicExtractor:72 - Found [-6411] as column [gid]
11:42:53,648 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [getString]
11:42:53,649 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [wasNull]
11:42:53,650 TRACE BasicExtractor:72 - Found [TQ9GY] as column [hdwr.nom]
11:42:53,650 TRACE AbstractResultSetProxyHandler:72 - Handling invocation of ResultSet method [next]
so on until DEBUG Loader:873 - Result set row: 6397
正如您所看到的，SQL查询返回标量值，而不是实体，因此实体管理不会产生任何开销。 那么，在解析结果时，hibernate执行的所有操作都解释了这种极端的开销吗？我认为在命名查询中为所有参数指定返回类型将简化hibernate作业，而不是让它猜测结果类型。我还能做些什么来加快休眠速度？
答案 0 :(得分：0)
似乎专门定义标量的结果类型是不够的，hibernate生成的解析结果集的开销仍然很大。我专门为我的查询设置了一个PassThroughResultTransformer，与JDBC查询相比，它有效地加快了解析。我的问题中第一个代码摘录的变化如下：
Query query = session.getNamedQuery("sql.namedquery.captureinfo");
query.setResultTransformer(PassThroughResultTransformer.INSTANCE);
Long t0 = System.currentTimeMillis();
List<Object[]> sqlList = query.list();
Long t1 = System.currentTimeMillis();
System.err.println("SQL query took" + (t1 - t0));