I'm currently developing multiple Web Services that need to access a common database.
I would like to use Entity Framework in order to interact with the DB.
What would be the best course of action in order to avoid possible concurrent operations from occurring ?
For example, I have a Web Service that manages User details in the DB. How can I avoid scenarios such as one Client deletes a User while another tries to update it ?
Furthermore, there's also the possibility of multiple Web Services having to share access to the same tables in the DB, which also brings concurrence problems.
Thanks
Note: I haven't decided yet if the Web Services themselves will be Singletons, but it might be a possibility. I have yet to determine if this will be beneficial...
This does not depend on WebServices or WCF.
When you create a classic Client/Server desktop application you also have concurrency issues to deal with.
What would be the best course of action in order to avoid possible concurrent operations from occurring ?
In general you don't. This would require some complicated and performance-killing locking code.
For example, I have a Web Service that
manages User details in the DB. How
can I avoid scenarios such as one
Client deletes a User while another
tries to update it ?
Just let it happen. One of the two will get an error. Your task is to handle that error, and present it to the user. You will have to handle errors anyway (lost connection).
Related
I have an application with a backend as database.
The application is sort of PUB-SUB model where users post changes to the application and other peers subscribe to those changes. These changes may happen very frequently or periodically and all the changes have to be written to database.
Now, I am being asked to find the possibility of replacing this RDBMS with LDAP. Probably they want unified DB for all applications but anyways I have to find the advantage/disadvantages of both approaches.
I cannot directly compare RDBMS a with LDAP as I have almost no idea of LDAP though I tried to get some.
I understand that LDAP is designed for directory access and is optimized for Read access, so it is write once and read many. I have read that frequent writes will reduce the performance of LDAP server as each write will result a trigger to indexing process.
Just to give a scenario in regards with indexing in LDAP, my table will have few columns say 2 viz. Name and Desc. Now in LDAP I suppose this would become two attributes as Name and Desc. In my scenario it's Desc which will be frequently updated. I assume Name will be indexed so even if Desc is changing frequently it won't trigger indexing process.
I point is worth mentioning that the database will be hosted on some cloud platform.
I tried to find out the differences but nothing conclusive I could find out.
LDAP is a protocol, REST is a service based on the HTTP (protocol). So when the LDAP server shall not be exposed to the internet, how do you want to get the data from it? As LDAP is the protocol you would need direct access to the LDAP-server. Its like a database server that you would not expose directly to the internet. You would build an interface to encapsulate it. and that might as well be a REST interface.
I'd try to get the point actos that one is the transfer protocol and a storage backend and the ither is the public interface to its data. It's a bit like why is mysql better than a webinterface. You'd never make the mysql-server publicly available but encapsulate its protocol into an application.
REST is an interface. It doesn't matter how you orgsnize your data behind that interface. When you decide that you want to organize it differently you can do so without the consumer of your API noticing any change. And you can provide different versions of your API depending on improvements of your service.
LDAP on the other hand is an implementation. You can't change the way your data is handled without the consumer noticing it. So there's no way to rearrange your backend without affecting the consumer.
With REST you can therefore change the backend from MySQL to PostgreSQL even to LDAP without notice which you won't be able with LDAP.
Hope that helps
Now that we finally know what you're actually asking, which has nothing to do with your title, the body of your question, or REST, the simple answer is that there is no particular reason to believe that an LDAP server will perform significantly better than an RDBMS in this application, with two riders:
it may not even be feasible, due to the schema issue, and
if it is feasible it may not be semantically suitable, due to the lack of ACID properties, lack of JOINs, and the other issues mentioned in comments.
I will state that this is one of the worst formulated questions I have seen here for some considerable time, and the difficulty of extracting the actual question was extreme.
I have two applications(web and a desktop app) that uses entity framework which use a common sql server database. They have unit of work pattern implemented and it keeps the context in the session or in the relevant thread. My question is how to update context of another application when one application updates something on the database ?
As an example let say the windows service has added some row to a table. How can the web application context get that one at the same time it is inserted.
Context in scenario of a web application should only last per the request. From what I see, you have to implement something as an event from database level as that seems to be the common place. This can be done using Triggers
In your scenario, you should perform following steps (just doing a drawing board scenario)
Add triggers at database level for each table, which will basically throw an event to the application layer.
Somehow extract those triggers into stored procedures, so that you can use with EF
Thereafter, implement a layer that sits on both the application whose primary responsibility is to notify the user of a change in the database by other application and then update the request by clicking a button(which in turn update the context). Basically the database level trigger, triggers something on the respective UI.
The meat of the work lies in the third point. You can achieve it in many ways. Alternatives are writing a service that polls another service (which accepts alerts from db trigger) for checking the modifications. so the logical separation could be like db --> service that accepts the change notification --> service that polls the notification service --> application
Above works logically and theoretically but hope it helps you out and I would be keen to know how you go about doing this.
I want to create my site and in the page have it so that the forum pages will use the forum mysql user having privileges on mydb.forum_table, mydb_forum_table2.
and the profile page to use the profile user having access to mydb.users and mydb.profiefields
and so on with the photogallery, blog, chat and...
is this the right way to do it! I'm thinking of principle of least privileges but I wonder why I haven't seen other big known CMS do it!
One of the critical resources for a database is connections. Generally databases are configured with a maximum number of connections, an each time a process needs to make a query, it needs a connection to do so. Database connections are expensive objects to create -- they take time and memory, and most importantly, connections are established for a specific user. The generally accepted 'best practice' for web applications is for the application, when it needs a database connection, to check a pool for an available connection. If there's a free connection in the pool, the web app will pull that connection, use it as necessary, and then return it to the pool for reuse. If there are no free connections, the app will create a new one, use it, and then place it in the pool for reuse.
If you're dealing with an application that uses multiple database users (for privilege management) and you need to use connection pooling, your application will need to establish many pools (one for each user), which will usually result in your application acquiring at least one connection for each database user it is using. This is inefficient, error prone, and needlessly complex.
If you're truly intent on limiting your application's access to data, then you should probably investigate how much support your database has for views. If views are well-supported, then you can create a view (or views) that are customized to the needs any given portion of your application.
My recommendation would be to stick to a single database user, and then use the time you just freed up to do more debugging of your application. You'll get better results, and will aggravate fewer DBAs.
If I understand correctly, the question is about implementing module access control based on the permissions on the tables that are used by the module.
I think it would be complicated to maintain (the link between modules, and tables), and slow to have to check the permissions on each table accessed by the module.
We are developing a project that involves about 10 different WCF services with several endpoints each. One of the services keeps a few big tables of data cached in memory.
We have found we need access to that data from another service. Rather than keeping 2 copies of the cache, I'd like to be able to share those tables across all services.
I have done some research and found some articles about using an IExtension attached to the servicehosts to store the shared data.
Provided that all the services are running under the same web site, will that work? And is it the right approach? Or should I be looking elsewhere?
If the data that you're caching is required by more than one service, it sounds like - from a Service Oriented Architecture perspective, anyway - that it doesn't belong in either of services you have calling it.
If the data being cached isn't really related to either service, but is something that both services need, then perhaps it belongs in it's own seperate service. Have you considered encapsulating your cache in a third service, and performing a service-to-service call to retrieve the data you need? Benefits include...
It solves your original dilemma, avoiding the need to read the whole cache from the database several times;
It encapsulates the cache in one place for easy maintainance/change later.
It allows you to abstract the implementation of the cache away from the other services by putting another service interface in the way.
All in all, I'd suggest that's the best approach. The only downside is the extra overhead of making the service-to-service call, but that surely outperforms having to read the whole cache from the database.
Alternatively, if the data in your cache is very closely related to BOTH of the services that are calling the cache, i.e. both services add/change the data in the cache, etc. then perhaps the two existing services should be combined into a single service.
If what I'm saying is making some sense, then then principle of SOA I'm drawing on is Service Autonomy.
Provided all your services are part of the same application there doesn't seem to be any reason why you can't share the cache directly via a shared object reference. The simplest way of doing this is via a static field.
If you choose this approach, one thing to be very careful about is thread safety. If your cache is concurrently accessed via two WCF sessions, you must ensure that the two sessions are not going to interfere with each other by both changing the cache at the same time. If the cache is read-only, your need to do this is lessened, but you still might need to synchronrise initialisation of the cache.
I am currently working on a project with specific requirements. A brief overview of these are as follows:
Data is retrieved from external webservices
Data is stored in SQL 2005
Data is manipulated via a web GUI
The windows service that communicates with the web services has no coupling with our internal web UI, except via the database.
Communication with the web services needs to be both time-based, and triggered via user intervention on the web UI.
The current (pre-pre-production) model for web service communication triggering is via a database table that stores trigger requests generated from the manual intervention. I do not really want to have multiple trigger mechanisms, but would like to be able to populate the database table with triggers based upon the time of the call. As I see it there are two ways to accomplish this.
1) Adapt the trigger table to store two extra parameters. One being "Is this time-based or manually added?" and a nullable field to store the timing details (exact format to be determined). If it is a manaully created trigger, mark it as processed when the trigger has been fired, but not if it is a timed trigger.
or
2) Create a second windows service that creates the triggers on-the-fly at timed intervals.
The second option seems like a fudge to me, but the management of option 1 could easily turn into a programming nightmare (how do you know if the last poll of the table returned the event that needs to fire, and how do you then stop it re-triggering on the next poll)
I'd appreciate it if anyone could spare a few minutes to help me decide which route (one of these two, or possibly a third, unlisted one) to take.
Why not use a SQL Job instead of the Windows Service? You can encapsulate all of you db "trigger" code in Stored Procedures. Then your UI and SQL Job can call the same Stored Procedures and create the triggers the same way whether it's manually or at a time interval.
The way I see it is this.
You have a Windows Service, which is playing the role of a scheduler and in it there are some classes which simply call the webservices and put the data in your databases.
So, you can use these classes directly from the WebUI as well and import the data based on the WebUI trigger.
I don't like the idea of storing a user generated action as a flag (trigger) in the database where some service will poll it (at an interval which is not under the user's control) to execute that action.
You could even convert the whole code into an exe which you can then schedule using the Windows Scheduler. And call the same exe whenever the user triggers the action from the Web UI.
#Vaibhav
Unfortunately, the physical architecture of the solution will not allow any direct communication between the components, other than Web UI to Database, and database to service (which can then call out to the web services). I do, however, agree that re-use of the communication classes would be the ideal here - I just can't do it within the confines of our business*
*Isn't it always the way that a technically "better" solution is stymied by external factors?