For some time I have been working with ZK and now I have an application hosted in the cloud but this does not meet my performance expectations. My application uses ZK for the view, Hibernate for the interaction with the MySQL database and Spring for the management of beans related to database interaction.
Example scenario:
At initialization a list is retrieved from the database using hibernate (we are talking about max 200 objects, max 6 standard attributes). This takes some time, but is acceptable.
I add or delete objects from the list I use #NotifyChange("list") to tell the view that the list has changed.
The list is updated but this takes long, in my opinion (~2 seconds)
Step 3 takes about as long as step 1 which I don't understand, the Spring managed objects for database interaction have yet been initialized. Another thing to note is that I don't reload the entire list from the database when adding or deleting an object from the list; A local copy is kept of the objects in the spring managed bean #Autowired to my ViewModels. (Yes, potentially out of sync with the database, but in my case not much of an issue) But this eliminates hibernate/spring/database as the bottleneck, right?.
Also I ran this on the localhost, and of course that is faster but still not instant as I would expect/want.
Now I thought that it might have to do something with the creation and deletion of objects in java related to lists. I did research on how the ZK binder works and how objects are updated but I can't find anything about how the binder handles updates on lists.
Does anyone know how the ZK binder updates a list in the view when in the viewmodel the method is annotated with #NotifyChange("listA") ? Does it actually throw away the old list and sets the whole new list, or does it somehow have a merge on differences?
Also comments on what else could be the bottleneck are very welcome!
Thanks in advance,
Robert
I assume you use Listbox to represent your list.
First you need to know, that zk uses the same data
structure for MVVM that it uses for MVC. This means
that it uses ListModel and the performance tips
are usefull for MVVM as well.
Of course zk can't implement the standart model
in a way, that it fits everybodys needs.
So what you have to do is implement your own
model. Usually the best is to extend from ListModelList.
This way you can smart update the list.
i work alot with ZK but i have never use #NotifyChange, when i want to reload the data of a grid or listbox I always render or load it all again. For me it works fine and fast in less than 1 second. Here is an example of my binding:
>
And yes, when the data changes i recall my method, load it again and works really fine.
#Listen("onCreate = #listboxSolicitudes")
public void loadList() {
List<ConsultasSolicitudes> listaConsulta = null;
listaConsulta = ConsultasSeguimientoDeSolicitudesDAO.obtenerSolicitudesAsignadas((Long) cbResponsable.getSelectedItem().getValue());
ListModelList<ConsultasSolicitudes> solModel = new ListModelList<ConsultasSolicitudes>(listaConsulta);
listboxSolicitudesAsignadas.setModel(solModel);
}
Maybe this can help you, but something must be wrong if it´s taking that long.
Related
I wanna ask about if we write query in controller instead model. does it have any effect? such as load data become slower or others?
the data that i want to use is over 1000.
if not, what makes the load of data slow in web.
like the ajax request is needed 4-5 sec, and some is until 1 minutes
There is virtually no difference between running a query in a controller or a model except for the small (negligible) amount of overhead a model adds (if it were me I wouldn't worry about it). If you want to adhere to the MVC design pattern, database queries are typically done in the model, not the controller. But this is more of a stylistic thing in CodeIgniter as it is not strictly enforced as it is in other frameworks that use ORM.
With that being said, if you are experiencing long execution times I would recommend not getting all the data at once, and instead using load more, pagination, datatables, or a similar system to reduce the amount of records selected at once to something more manageable depending on your acceptable execution/response times.
You can test what works in your situation best by setting benchmark points: https://www.codeigniter.com/user_guide/libraries/benchmark.html
I have been working with CodeIgniter for some few years and what I have realized is to properly do your queries in models.
The idea of MVC is about code separation where the M(Model) handles or does the heavy liftings of the application which mostly relates to databases, the V(View) does the presentation that is where users of the system get to interact with the application and the C(Controller) acts as a messenger or intermediary between the Model and the View.
This releases the controller from lots of processes so that it doesn't have to query from the database, try to upload lots of data before then showing it on a view.
I always use the (I call it the little magic) {elapsed_time} and {memory_usage}to check how my application work per whatever logic I implement, you can give it a try.
I think this helps.
So I'm currently diving the CQRS architecture along with the EventStore "pattern".
It opens applications to a new dimension of scalability and flexibility as well as testing.
However I'm still stuck on how to properly handle data migration.
Here is a concrete use case:
Let's say I want to manage a blog with articles and comments.
On the write side, I'm using MySQL, and on the read side ElasticSearch, now every time a I process a Command, I persist the data on the write side, dispatch an Event to persist the data on the read side.
Now lets say I've some sort of ViewModel called ArticleSummary which contains an id, and a title.
I've a new feature request, to include the article tags to my ArticleSummary, I would add some dictionary to my model to include the tags.
Given the tags did already exist in my write layer, I would need to update or use a new "table" to properly use the new included data.
I'm aware of the EventLog Replay strategy which consists in replaying all the events to "update" all the ViewModel, but, seriously, is it viable when we do have a billion of rows?
Is there any proven strategies? Any feedbacks?
I'm aware of the EventLog Replay strategy which consists in replaying
all the events to "update" all the ViewModel, but, seriously, is it
viable when we do have a billion of rows?
I would say "yes" :)
You are going to write a handler for the new summary feature that would update your query side anyway. So you already have the code. Writing special once-off migration code may not buy you all that much. I would go with migration code when you have to do an initial update of, say, a new system that requires some data transformation once off, but in this case your infrastructure would exist.
You would need to send only the relevant events to the new handler so you also wouldn't replay everything.
In any event, if you have a billion rows of data your servers would probably be able to handle the load :)
Im currently using the NEventStore by JOliver.
When we started, we were replaying our entire store back through our denormalizers/event handlers when the application started up.
We were initially keeping all our data in memory but knew this approach wouldn't be viable in the long term.
The approach we use currently is that we can replay an individual denormalizer, which makes things a lot faster since you aren't unnecessarily replaying events through denomalizers that haven't changed.
The trick we found though was that we needed another representation of our commits so we could query all the events that we handled by event type - a query that cannot be performed against the normal store.
I have a n-tier application based on pretty classic different layers: User Interface, Services (WCF), Business Logic and Data Access.
Database (Sql Server) is obviously quered throught Entity Framework, the problem is basically that every call starts from user interface and go throught all the layers, but doing that I need to create a new ObjectContext each time for every operation and that makes performance very bad because every time I need to reload metadata and recompile the query.
The most suggested pattern it would be the one below and it is what I'm actually doing: creating and passing the new context throught business layer methods each time the service receives a call
public BusinessObject GetQuery(){
using (MyObjectContext context = new MyObjectContext()){
//..do something } }
For easy query I don't see any particular dealy and it works fine but for complex and heavy query it makes a 2 seconds query to keep going for like 15 seconds each call.
I could set the ObjectContext static and it would solve the performance issue but it appears to be not suggested by anyone, also because I won't be able to access the context at the same time from different thread and multiple calls raise an exception. I could make it thread-safe but mantain the same ObjectContext for long time makes it bigger and bigger (and slower) because the reference it imports each query it execute a query.
The architecture I have I think it is the most common so what is the best and known way to implement and use ObjectContext?
Thank you,
Marco
In a Web context, it's best to use a stateless approach and create an ObjectContext for each request.
The cost of ObjectContext construction are minimal. The metadata is loaded from a global cache so only the first call will have to load it.
Static is definitely not a good idea. The ObjectContext is not thread save and this will lead to problems when using it in a WCF service with multiple calls. Making it thread save will result in less performance and it can cause subtle errors when reusing it in multiple requests.
Check this info: How to decide on a lifetime for your ObjectContext
Working with a static object context is not a good idea. A static context will be shared by all users of the web application meaning that when one user makes modifications to a context such as calling saveChanges , all other users using the context will be affected (this would be a problem when supposing they have added or updated data to the context but have not called save changes). The best practice while working with object context is to keep it alive for the period of the request and use if to perform any atomic business operations. You would want to check out the UnitOfWork pattern and repository pattern
uow
uow and repository in EF
If you feel you are having performance issues with your queries and there is a possibility that you would reuse your query , I would recommend you use precompiled linq queries. You can check out the links below for more info
precompiled linq julie lermann
precompiled linq
What you show is the typical pattern to use a context - by request, similar to using a database connection.
What makes you think the bad performance is related to recreating the context? This is very, very likely not the case. How did you measure this impact?
If you have such performance critical code that this overhead truly matters you should not use Entity Framework since there always will be some overhead, even if the overhead should be very little in the general case. I would start focusing on your data model though and the underlying data store which will have a much larger impact on your query performance. Have you optimized your queries? Did you put indexes everywhere you need them? Can you de-normalize the data to remove joins?
I have an application with about 20 models and controllers and am not using any particular framework. What is the best practice for using multiple remote objects in Flex performance-wise?
1) Method 1 - One per Component - Each component instantiates a RemoteObject for itself
2) Method 2 - Multiple in Application Root - Each controller is handled by a RemoteObject in the root
3) Method 3 - One in Application Root - Combine all controllers into one class and handle them with one RemoteObject
I'm guessing 3 will have the best performance but will be too messy to maintain and 1 would be the cleanest but would take a performance hit. What do you think?
Best practice would be "none of the above." Your Views should dispatch events that a controller or Command component would use to call your service(s) and then update your model on return of the data. Your Views would be bound to the data, and then the Views would automatically be updated with the new data.
My preference is to have one service Class per different piece or type of data I am retrieving--this makes it easier to build mock services that can be swapped for real services as needed depending on what you're doing (for instance if you have a complicated server setup, a developer who is working on skinning would use the mocks). But really, how you do that is a matter of personal preference.
So, where do your services live, so that a controller or command can reach them? If you use a Dependency Injection framework such as Robotlegs or Swiz, it will have a separate object that handles instantiating, storing, and and returning instances of model and service objects (in the case of Robotlegs, it also will create your Command objects for you and can create view management objects called Mediators). If you don't use one of these frameworks, you'll need to "roll your own," which can be a bit difficult if you're not architecturally minded.
One thing people who don't know how to roll their own (such as the people who wrote the older versions of Cairngorm) tend to fall back on is Singletons. These are not considered good practice in this day and age, especially if you are at all interested in unit testing your work. http://misko.hevery.com/code-reviewers-guide/flaw-brittle-global-state-singletons/
A lot depends on how much data you have, how many times it gets refreshed from the server, and of you have to support update as well as query.
Number 3 (and 2) are basically a singletons - which tends to work best for large applications and large datasets. Yes, it would be complex to maintain yourself, but that's why people tend to use frameworks (puremvc, cairgorm, etc). much of the complexity is handled for you. Caching data within the frameworks also enhances performance and response time.
The problem with 1 is if you have to coordinate data updates per component, you basically need to write a stateless UI, always retrieving the data from the server on each component visibility.
edit: I'm using cairgorm - have ~ 30 domain models (200 or so remote calls) and also use view models. some of my models (remote object) have 10's of thousands of object instances (records), I keep a cache with/write back. All of the complexity is encapsulated in the controller/commands. Performance is acceptable.
In terms of pure performance, all three of those should perform roughly the same. You'll of course use slightly more memory by having more instances of RemoteObject and there are a couple of extra bytes that get sent along with the first request that you've made with a given RemoteObject instance to your server (part of the AMF protocol). However, the effect of these things is negligible. As such, Amy is right that you should make a choice based on ease of maintainability and not performance.
If I expose IQueryable from my service layer, wouldn't the database calls be less if I need to grab information from multiple services?
For example, I'd like to display 2 separate lists on a page, Posts and Users. I have 2 separate services that provides a list of these. If both provides IQueryable, will they be joint in 1 database call? Each repository creates a context for itself.
It's best to think of an IQueryable<T> as a single query waiting to be run. So if you return 2 IQueryable<T> instances and run them in the controller, it wouldn't be any different than running them separably in their own service methods. Each time you execute the IQuerable<T> to get results, it will run the query by itself independent of other IQuerable<T> objects.
The only time (as far as I know) it will make an impact if there is enough time between the two service calls that the database connection might close, but you would need a considerable amount of time in between the service calls for that to be the case.
Returning IQuerable<T> to the controller still has some usefulness, such as easier handling of paging and sorting (so sorting is done on the controller and is not done on the service layer which doesn't necessarily care about how data is sorted or paged). This isn't a performance concern though, and people will disagree about if it's best to do this in the controller or not (I've seen reputable developers do this and give well thought out reasons why).
No. The best an IQueryable can do is reduce the number of calls within a singular database context. An IQueryable will not cross contexts.
Personally, I don't use IQueryables past the repositories for a number of reasons:
1) I don't use the same domain objects as database objects, and seeing "no translation to SQL" pisses me off ;)
2) I don't like the necessary structure for IQueryables in views: foreach (var item in collection){var tempItem = item; code on tempItem}
3) I've come up with a method of passing generic filters to the data layer (LinqKit and PredicateBuilder are gods)
If these reasons don't apply to you, of course you should feel free to use IQueryables to whichever layer you desire.
Not with two different contexts.
Definitely NO. It's a leaky abstraction.
It allows abominations like this:
q.Where(x=>{Console.WriteLine("fail");return true;});
Thing is - when exposing IQueryable, You are saying that Your data layer fully supports linq to objects.
If you make two method calls you will make two queries.
You can combine the methods into a single method which gets all the data at once.
If you are implementing the repository pattern you will have an easier time if you instantiate one database context per request.
Your service layer is exactly that, a layer which serves up what you need. Often times my service layers are named things like SearchService which has methods for returning every packaged collection I will ever need (the actual view models themselves). And if I ever need a new search, my service layer gets a new method. The backing for your service layer can then contain any data backing or persistence model you would like, be it a repository or Entity Framework provider, etc.
To answer your question though, the line needs to be drawn at the service layer, all queries need to be contained within it and only data returned.