java – Hibernate比sql查询慢1000倍

我有这个设置@Table(name =A)EntityA {Long ID;ListEntityB children;}@Table(name =B)EntityB {Long ID;EntityA parent;EntityC grandchild;}@Table(name =C)EntityC {Long ID;}SQL查询是这样的(我省...

我有这个设置

@Table(name ="A")
EntityA {
    Long ID;
    List<EntityB> children;
}

@Table(name ="B")
EntityB {
    Long ID;
    EntityA parent;
    EntityC grandchild;
}

@Table(name ="C")
EntityC {
    Long ID;
}

SQL查询是这样的(我省略了不相关的细节)：

select top 300 from A where ... and ID in (select parent from B where ... and grandchild in (select ID from C where ...)) order by ...

直接数据库中的sql查询或通过Hibernate(3.5)SQL运行比使用Criteria或HQL表达快1000倍.

生成的SQL与HQL和Criteria以及我在那里发布的SQL完全相同.

[编辑]：更正 – sql不完全相同.我没有在管理工作室方面尝试Hibernate样式参数设置,因为直到后来我才意识到这一点 – 请参阅我的回答.

如果我将子查询分成单独的查询,那么它再次快速.

我试过了

>删除子,父,等等的所有映射,并使用Long Id引用 – 同样的事情,所以它不是一个吸引人的,懒惰的,渴望相关的.
>使用连接而不是子查询,并获取与获取和加载的所有组合相同的慢速行为.
>在ID上设置投影而不是检索实体,因此没有对象转换 – 仍然很慢

我查看了Hibernate代码,它正在做一些惊人的事情.它有一个循环遍历所有300个结果,最终命中数据库.

private List doQuery(
        final SessionImplementor session,
        final QueryParameters queryParameters,
        final boolean returnProxies) throws SQLException, HibernateException {

    final RowSelection selection = queryParameters.getRowSelection();
    final int maxRows = hasMaxRows( selection ) ?
            selection.getMaxRows().intValue() :
            Integer.MAX_VALUE;

    final int entitySpan = getEntityPersisters().length;

    final ArrayList hydratedObjects = entitySpan == 0 ? null : new ArrayList( entitySpan * 10 );
    final PreparedStatement st = prepareQueryStatement( queryParameters, false, session );
    final ResultSet rs = getResultSet( st, queryParameters.hasAutoDiscoverScalarTypes(), queryParameters.isCallable(), selection, session );

// would be great to move all this below here into another method that could also be used
// from the new scrolling stuff.
//
// Would need to change the way the max-row stuff is handled (i.e. behind an interface) so
// that I could do the control breaking at the means to know when to stop

    final EntityKey optionalObjectKey = getOptionalObjectKey( queryParameters, session );
    final LockMode[] lockModesArray = getLockModes( queryParameters.getLockOptions() );
    final boolean createSubselects = isSubselectLoadingEnabled();
    final List subselectResultKeys = createSubselects ? new ArrayList() : null;
    final List results = new ArrayList();

    try {

        handleEmptyCollections( queryParameters.getCollectionKeys(), rs, session );

        EntityKey[] keys = new EntityKey[entitySpan]; //we can reuse it for each row

        if ( log.isTraceEnabled() ) log.trace( "processing result set" );

        int count;
        for ( count = 0; count < maxRows && rs.next(); count++ ) {

            if ( log.isTraceEnabled() ) log.debug("result set row: " + count);

            Object result = getRowFromResultSet( 
                    rs,
                    session,
                    queryParameters,
                    lockModesArray,
                    optionalObjectKey,
                    hydratedObjects,
                    keys,
                    returnProxies 
            );
            results.add( result );

            if ( createSubselects ) {
                subselectResultKeys.add(keys);
                keys = new EntityKey[entitySpan]; //can't reuse in this case
            }

        }

        if ( log.isTraceEnabled() ) {
            log.trace( "done processing result set (" + count + " rows)" );
        }

    }
    finally {
        session.getBatcher().closeQueryStatement( st, rs );
    }

    initializeEntitiesAndCollections( hydratedObjects, rs, session, queryParameters.isReadOnly( session ) );

    if ( createSubselects ) createSubselects( subselectResultKeys, queryParameters, session );

    return results; //getResultList(results);

}

在这段代码中

final ResultSet rs = getResultSet( st, queryParameters.hasAutoDiscoverScalarTypes(), queryParameters.isCallable(), selection, session );

它使用完整的SQL命中数据库,但在任何地方都没有收集结果.

然后它继续经历这个循环

for ( count = 0; count < maxRows && rs.next(); count++ ) {

对于预期的300个结果中的每一个,它最终会访问数据库以获得实际结果.

这看起来很疯狂,因为在1次查询后它应该已经有了所有结果. Hibernate日志不会显示在此期间发出的任何其他SQL.

有人有任何见解吗？我唯一的选择是通过Hibernate转到本机SQL查询.

解决方法:

我终于成功了解了这一点.问题是由Hibernate将参数与涉及子查询的实际SQL查询分开设置引起的.如此原生SQL,如果这样做,性能将会很慢.例如,这将是缓慢的：

String sql = some sql that has named parameter = :value
SQLQuery sqlQuery = session.createSQLQuery(sql);
sqlQuery.setParameter ("value", someValue);
List<Object[]> list = (List<Object[]>)sqlQuery.list();

这将是快速的

String sql = some native sql where parameter = 'actualValue'
SQLQuery sqlQuery = session.createSQLQuery(sql);
List<Object[]> list = (List<Object[]>)sqlQuery.list();

似乎由于某些原因让Hibernate处理参数,它最终会被卡在resultSet中.这可能是因为数据库的基础查询花费了更长的时间进行参数化.我最终编写了相当于Hibernate Criteria和Restrictions代码的代码,它直接如上所述设置参数.