Hibernate Query Optimization and lazy loading
The problem:
For each object that Hibernate loads, it needs to do one or more extra SQL queries to load associated objects. (Potentially as many as Kn + 1, where n is the number of objects returned).
Example:
-
Simplified hibernate mapping file
<class name=”Department”>
…
<many-to-one name=”employee”…/>
…
</class>
-
Simple HQL Query
from Department dept where dept.location like :LOCATION
- The generated SQL statements:
-
At least the initial select.
select dept_id, deplt_name, dept_location…from department…
-
Then a sequence of selects from the associated table. (n sql select statements)
Select …from employee…
Select …from employee…
Select …from employee…
…
If Sale table returns 100 rows, you will see 100 select statements extra more than the main select statement.
The solution (1):
The association objects must be loaded in the initial query and just when you need them. This can be done by adding ‘left join fetch’ for example and switching the lazy loading on.
from Department dept left join fetch dept.employee
where dept.location like :LOCATION
This will generate just one sql select statement.
The solution (2): When there are a lot of association tables
You don’t want to end up with query like this:
from Department dept
left join fetch dept.employee
left join fetch dept.manager
left join fetch dept.building
left join fetch dept.level
left join fetch dept.city
…etc
The approach involves determining exactly which columns you really need, and instantiating data-transfer objects containing exactly those columns.
Select new Department (dept.id, dept.employee.name, dept.manager.name, …) from Department dept
…
This technique is fast and efficient, and avoids the overheads of handling associated objects and of loading large numbers of persistent objects into the Hibernate session cache. The only downside is the need to create a dedicated data-transfer class for each query, and an overloaded constructor.
Reference: http://www.javalobby.org/articles/hibernate-query-101/In: Hibernate, IT · Tagged with: Hibernate, Open Source
IIS7 as Web Server – Application Request Routing
We used this approach to forward all requests from/to MOSS 2007. It is easy using IIS7 but complicated with IIS6
- Install IIS 7
- Install Application Request Routing http://learn.iis.net/page.aspx/482/install-application-request-routing/
- Open IIS Manager
Press Add and then Finish
Press Yes
Try to request for a page on MOSS server from the web server.
http://WEB_SERVER/Pages/Memos.aspx
This will be forward the request to MOSS server
http://WEB_SERVER/Pages/Memos.aspx to http://MOSS:PORT/Pages/Memos.aspx
The client will not notice this!
For IIS6 (To send request from one IIS6 to another one an delegate user login information)
We have managed successfully to configure IIS 6 as reverse proxy and delegate authentication to the second IIS 6 using ISAPI_Rewrite version 2. Previously, we were using the latest version of ISAPI_Rewrite 3.0 , the documentation of this version mentions that is working with basic authentication , but it didn’t work with us. Basic authentication is supported with version 2, Now we have managed successfully to delegate authentication to from one IIS to other one with extra configuration on both IIS servers & ISAPI_Rewrite. All users must be a domain users and visible by both IIS servers to get the user be authenticated.
In: IT, Microsoft, SharePoint · Tagged with: IIS7, MOSS, SharePoint, WebServer