问题
I have the following hibernate query:
Query query = session.createQuery(\"from MyHibernateClass\");
List<MyHibernateClass> result = query.list();// executes in 7000ms
When logging the sql being executed in MySQL I see
select
myhibernat0_.myFirstColumn as myfirstcolumn92_,
myhibernat0_.mySecondColumn as mysecondcolumn92_,
myhibernat0_.mythirdcolumn as mythirdcolumn92_,
myhibernat0_.myFourthColumn as myfourthcolumn92_
from MyHibernateClass myhibernat0_
where (1=1);
When measurering the java code in the jvm on a small dataset of 3500 rows in MyHibernateClass database table this takes about 7000ms.
If I on the otherhand uses direct jdbc as follows:
Statement statement = session.connection().createStatement();
ResultSet rs = statement.executeQuery(\"select * from MyHibernateClass\");// 7ms
List<MyHibernateClass> result = convert(rs);// executes in 20ms
I see the same sql going into the database but now the time spend in the java code in the jvm is 7ms.
The MyHibernateClass is a simple java bean class with getters and setters, I use no special resulttransformers as can be seen in the example. I only need a read-only instance of the class, and it doesn\'t need to be attached to the hibernate session.
I would rather like to use the hibernate version but cannot accept the execution times.
Added information: After adding hibernate logging I see
[2011-07-07 14:26:26,643]DEBUG [main] [logid: ] -
org.hibernate.jdbc.AbstractBatcher.logOpenResults(AbstractBatcher.java:426) -
about to open ResultSet (open ResultSets: 0, globally: 0)
followed by 3500 of the following log statements
[2011-07-07 14:26:26,649]DEBUG [main] [logid: ] -
org.hibernate.loader.Loader.getRow(Loader.java:1197) -
result row: EntityKey[com.mycom.MyHibernateClass#1]
followed by 3500 log statements like
[2011-07-07 14:27:06,789]DEBUG [main] [logid: ] -
org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:130) -
resolving associations for [com.mycom.MyHibernateClass#1]
[2011-07-07 14:27:06,792]DEBUG [main] [logid: ] -
org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:226) -
done materializing entity [com.mycom.MyHibernateClass#1]
What does this mean?
What is Hibernate doing in the first implementation, how can I find out?
回答1:
Adding a constructor with all attributes of the class did the trick, now the execution times are 70ms for the hibernate query. Previously the class only had a default constructor without arguments and a constructor with the entity id argument.
回答2:
Based on the new information I felt I should provide another answer. The difference looks like that you have a one-to-many association specified for a List or Set property in your bean.
You are probably specifying that lazy=false which will turn off lazy loading. With lazy loading turned off it will fetch every associated record for every MyHibernateClass entity and this is why it is taking so long to execute.
Try setting lazy=true and this will perform much faster and then only retrieve the associated entities when explicitly requesting them from the entity.
回答3:
If you utilize Log4j in your application you can set a variety of different logging options specific to Hibernate to get a better picture of what is going on behind the scenes in Hibernate.
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/session-configuration.html#configuration-logging
My guess is that this is the typical initial load time that occurs when first calling an HQL query in an application. Subsequent HQL queries should be noticeably and considerably faster after this first one.
回答4:
I know this thread is old, but to update I ran into the same problem but with SQL Server and it turns out to be that SQL being printed by Hibernate and SQL Sent using the driver is different. Using MSSQL Driver by default sends the queries as stored procedures as RPC calls it's because the driver tries to optimize the query plan for MSSQL Standards , so it sends the queries something like
Hibernate Query:
select c.col1,c.col2 from customer c where c.name like @param1 and c.country like @param2
Actual Driver Sent Query:
@param1=somevalue, @param2=somevalue
declar sp ....
select c.col1,c.col2 from customer c where c.name like @param1 and c.country like @param2
go
Note: This Query I got through SQL Profiler Tool directly listening on DB
It turns out to be that sp_exec optimizations on the MSSQL tend to produce good Query plans that's get cached, but this would result in 'parameter sniffing' to know more about this problem read here...
So to overcome this I had following options:
Change my HQL to native Queries and add OPTION RECOMPILE FOR SOME PARAM
Use Direct query values instead of prepared statements so there will be no translation for param values and queries will not be modified as Stored Procedures by the Driver
Change the driver settings to not send the stored procedures (this is still bad because now the query plans in MSSQL server will be specific to this query, this is same as Option:2 but outside the code)
I didn't want to use OPTION 1 & 2 since that eliminates the whole purpose of using ORM Frameworks and I end up using OPTION 3 for now
So I changed the JDBC URL to send option prepareStatement=false
After setting this I had one more problem the query being sent like
Select * from customer c where c.name like **N**'somename' and c.country=**N**'somevalue'
Here there is a prefix before the values which states that to convert the encoding scheme , so I disable the JDBC url to sendUnicode = false
This all I did in JTDS driver options.. As far as I am concerned now the application is up and running fast. I have also introduced second level caches to cache it for some time..
Hope this helps for someone, if you have any good suggestion please let me know.
回答5:
I know this is an old question but here is what fixed it for me...
In your hibernate.cfg.xml make sure you have the correct !DOCTYPE... it should be as follows:
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
回答6:
I had an incident where my application was always using every row in the result set of a query. I found a 40-fold increase in speed by setting my fetch size using the setFetchSize method below. (The performance improvement includes the addition of the count query.)
Long count = getStoreCount(customerId);
Query query = session.getNamedQuery("hqlGetStoresByCustomerId")
.setString("i_customerid",customerId)
.setFetchSize(count.intValue());
Be careful while doing this; my data set had about 100 rows, and it was scoped to a the life of a web request. If you have larger data sets, you will be eating Java Heap for the duration of the existence of that data, prior to returning it to the Java Heap.
回答7:
It took me 10 seconds to execute a simple select all query before I found out that DOCTYPE tag is written wrongly in hibernate.cfg.xml and *mapping object*.hbm.class
Make sure that hibernate.cfg.xml start with
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
And mapping xml.class with
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
Now it took me 1-2 seconds to execute any queries.
来源：https://stackoverflow.com/questions/6609645/simple-hibernate-query-returning-very-slowly