Strategies for Fixing Problems / Tweaking NHibernate Apps in Production - nhibernate

First off, I am not a DBA, but I do work in an environment where DBAs do tune/make changes in the production database from time to time in ways that do not cause the need for an application rebuild/redeployment. Usually these changes consist of reworking indexes, changing procs, and sometimes changing the table structure in minor ways (usually abstracted from the app via procs).
Obviously, a team should strive to catch performance problems with NHibernate before they get into production using things like NHProf, SQL Profiler, and load tests. That being said, are there certain strategies that can be used to allow some amount of tweaking once the code is built and out running in production? Using stored procedures 100% of the time seems like it would allow the most flexibility for the DBA's, but obviously that would really kill the efficiency of NHibernate. From what I've read, updatable views (in SQL Server) don't really work that well with NHibernate either (this may-or-may-not be true).
I've read quite a bit about NHibernate and experimented with it over the years, but I have never put it into practice in a production environment. I have yet to come across a set of "best practices" to allow for maximum tweaking once deployed.
As an NHibernate user, how are you and your team dealing with issues if they arise in production? My production environment is made up of ASP.NET apps and SQL server, but I don't think the answers need to be restricted to that platform.

I am in a similar position, and in order to keep our DBA happy, I did the following:
Wrote some of the queries in HQL, some others in SQL (especially those perf-sensitive)
Externalized those queries to files, one file per query.
When your app needs to execute of these queries, it just loads the appropriate file, optionally running it through a pre-processor, and runs it.
With this approach, the DBA could theoretically tweak the queries just by modifying those files. That's quite similar to having stored procedures.
In practice, it's up to you to decide if you'll really give the DBA access to those files (if you catch my drift...)
IMHO the DBA should just use the DBMS's profiling tools and report her findings back to the devs (as in "there's this query that is running 20 times/sec and does 10 joins. is that really necessary? can it be cached? do you really need all those joins? can we denormalize this?" etc.

I'm not in the deploy phase yet, but on my current project I've come up against this already and my solution presently has been to replace my queries with stored procs. As long as the shape of the data coming back from the DB remains the same it's not a big deal. Yeah you do lose some of that agility you enjoyed during development but I'm not sure it's as bad as it initially sounds. You'll have a code push when you first make the change of course, and then from that point it's just proc changes.

You can use a profiler like NHProf to see the sql queries executed, so you can show them to a DBA. This tool can also detect some problem like n+1 select.
Using a second level of cache can be useful : http://web.archive.org/web/20110514214657/http://blogs.hibernatingrhinos.com/nhibernate/archive/2008/11/09/first-and-second-level-caching-in-nhibernate.aspx

Related

When should I use stored procedures?

When should I be using stored procedures instead of just writing the logic directly in my application? I'd like to reap the benefits of stored procedures, but I'd also like to not have my application logic spread out over the database and the application.
Are there any rules of thumb that you can think of in reference to this?
Wow... I'm going to swim directly against the current here and say, "almost always". There are a laundry list of reasons - some/many of which I'm sure others would argue. But I've developed apps both with and without the use of stored procs as a data access layer, and it has been my experience that well written stored procedures make it so much easier to write your application. Then there's the well-documented performance and security benefits.
This depends entirely on your environment. The answer to the question really isn't a coding problem, or even an analysis issue, but a business decision.
If your database supports just one application, and is reasonably tightly integrated with it, then it's better, for reasons of flexibility, to place your logic inside your application program. Under these circumstances handling the database simply as a plain data repository using common functionality looses you little and gains flexibility - with vendors, implementation, deployment and much else - and many of the purist arguments that the 'databases are for data' crowd make are demonstratively true.
On the other hand if your are handling a corporate database, which can generally be identified by having multiple access paths into it, then it is highly advisable to screw down the security as far as you can. At the very least all appropriate constraints should enabled, and if possible access to the data should be through views and procedures only. Whining programmers should be ignored in these cases as...
With a corporate database the asset is valuable and invalid data or actions can have business-threatening consequences. Your primary concern is safeguarding the business, not how convenient access is for your coders.
Such databases are by definition accessed by more than one application. You need to use the abstraction that stored procedures offer so the database can be changed when application A is upgraded and you don't have the resource to upgrade application B.
Similarly the encapsulation of business logic in SPs rather than in application code allows changes to such logic to be implemented across the business more easily and reliably than if such logic is embedded in application code. For example if a tax calculation changes it's less work, and more robust, if the calculation has to be changed in one SP than multiple applications. The rule of thumb here is that the business rule should be implemented at the closest point to the data where it is unique - so if you have a specialist application then the logic for that app can be implemented in that app, but logic more widely applicable to the business should be implemented in SPs.
Coders who dive into religious wars over the use or not of SPs generally have worked in only one environment or the other so they extrapolate their limited experience into a cast-iron position - which indeed will be perfectly defensible and correct in the context from which they come but misses the big picture. As always, you should make you decision on the needs of the business/customers/users and not on the which type of coding methodology you prefer.
I tend to avoid stored procedures. The debugging tools tend to be more primitive. Error reporting can be harder (vs your server's log file) and, to me at least, it just seems to add another language for no real gain.
There are cases where it can be useful, particularly when processing large amounts of data on the server and of course for database triggers that you can't do in code.
Other than that though, I tend to do everything in code and treat the database as a big dump of data rather than something I run code on.
Consider Who Needs Stored Procedures, Anyways?:
For modern databases and real world
usage scenarios, I believe a Stored
Procedure architecture has serious
downsides and little practical
benefit. Stored Procedures should be
considered database assembly language:
for use in only the most performance
critical situations.
and Why I do not use Stored Procedures:
The absolute worst thing you can do,
and it's horrifyingly common in the
Microsoft development world, is to
split related functionality between
sproc's and middle tier code.
Grrrrrrrr. You just make the code
brittle and you increase the
intellectual overhead of understanding
a system.
I said this in a comment, but I'm going to say it again here.
Security, Security, SECURITY.
When sql code is embedded in your application, you have to expose the underlying tables to direct access. This might sound okay at first. Until you get hit with some sql injection that scrambles all the varchar fields in your database.
Some people might say that they get around this by using magic quotes or some other way of properly escaping their embedded sql. The problem, though, is the one query a dev didn't escape correctly. Or, the dev that forgot to not allow code to be uploaded. Or, the web server that was cracked which allowed the attacker to upload code. Or,... you get the point. It's hard to cover all your bases.
My point is, all modern databases have security built in. You can simply deny direct table access (select, insert, update, and deletes) and force everything to go through your s'procs. By doing so generic attacks will no longer work. Instead the attacker would have to take the time to learn the intimate details of your system. This increases their "cost" in terms of time spent and stops drive by and worm attacks.
I know we can't secure ourselves against everything, but if you take the time to architect your apps so that the cost to crack it far outweighs the benefits then you are going to serious reduce your potential of data loss. That means taking advantage of all the security tools available to you.
Finally, as to the idea of not using s'procs because you might have to port to a different rdbms: First, most apps don't change database servers. Second, in the event that it's a real possibility, you have to code using ANSI sql anyway; which you can do in your procs. Third, you would have to reevaluate all of your sql code no matter what and it's a whole lot easier when that code is in one place. Fourth, all modern databases now support s'procs. Fifth, when using s'proc's you can custom tune your sql for the database it's running under to take advantage of that particular database's sql extensions.
Basically when you have to perform operations involving data that do not need to get out of the database. For example, you want to update one table with data from another, it makes little sense to get the data out and then back in if you can do it all in one single shot to the db.
Another situation where it may be acceptable to use stored procedures is when you are 100% sure you will never deploy your application to another database vendor. If you are an Oracle shop and you have lots of applications talking to the same database it may make sense to have stored procedures to make sure all of them talk to the db in a consistent manner.
Complicated database queries for me tend to end up as stored procs. Another thought to consider is that your database might be completely separate and distinct from the application. Lets say you run an Oracle DB and you essentially are building an API for other application developers at your organization to call into. You can hide the complicated stuff from them and provide a stored proc in its place.
A very simple example:
registerUser(username, password)
might end up running a few different queries (check if it exists, create entries in a preference table, etc) and you might want to encapsulate them.
Of course, different people will have different perspectives (a DBA versus a Programmer).
I used stored procs in 1 of 3 scenarios:
Speed
When speed is of the utmost importance, stored procedures provide an excellent method
Complexity
When I'm updating several tables and the code logic might change down the road, I can update the stored proc and avoid a recompile. Stored procedures are an excellent black box method for updating lots of data in a single stroke.
Transactions
When I'm working an insert, delete or update that spans multiple tables. I wrap the whole thing in a transaction. If there is an error, it's very easy to roll back the transaction and throw an error to avoid data corruption.
The bottom 2 are very do-able in code. However, stored procedures provide an black-box method of working when complex and transaction level operations are important. Otherwise, stick with code level database operations.
Security used to be one of the reasons. However, with LINQ and other ORMs out there, code level DAL operations are much more secure than they've been in the past. Stored procs ARE secure but so are ORMs like LINQ.
We use stored procedures for all of our reporting needs. They can usually retrieve the data faster and in a way that the report can just spit out directly instead of having to do any kind of calculations or similar.
We also will use stored procedures for complex or complicated queries we need to do that would be difficult to read if they were otherwise inside of our codebase.
It can also be very useful as a matter of encapsulation and in the philosophy of DRY. For instance I use stored functions for calculations inside a table that I need for several queries inside the code. This way I use the better performance as well as the ensuring that the calculation is always done the same way.
I would not use it for higher functionality or logic the should be in the business logic layer of an architecture, but focused on the model layer, where the functionality is clearly focused on the database design and possible flexibility of changing the database design without breaking the API to the other layers.
I tend to always use stored procedures. Personally, I find it makes everything easier to maintain. Then there is the security and performance considerations.
Just make sure you write clean, well laid out and well documented stored procedures.
When all the code is in a stored proc, it is far easier to refactor the database when needed. Changes to logic are far easier to push as well. It is also far far easier to performance tune and sooner or later performance tuning becomes necessary for most database applications.
From my experience, stored procedures can be very useful for building reporting databases/pipelines, however, I'd argue that you should avoid using stored procedures within applications as they can impede a team's velocity and any security risks of building queries within an application can be mitigated by the use of modern tooling/frameworks.
Why might we avoid it?
To avoid tight-coupling between applications and databases. If we use stored procedures, we won't be able to easily change our underlying database in the future because we'd have to either:
Migrate stored procedures from one database (e.g. DB2) to another (e.g. SQL Server) which could be painstakingly time-consuming or...
Migrate all the queries to the applications themselves (or potentially in a shared library)
Because code-first is a thing. There a several ORMs which can enable us to target any database and even manage the table schemas without ever needing to touch the database. ORMs such as Entity Framework or Dapper allow developers to focus on building features instead of writing stored procedures and wiring them up in the application.
It's yet another thing that developers need to learn in order to be productive. Instead, they can write the queries as part of the applications which makes the queries far simpler to understand, maintain, and modify by the developers who are building new features and/or fixing bugs.
Ultimately, it depends on what developers are most comfortable with.
If a developer has a heavy SQL background, they might go with Stored Procs.
If a developer has lots of app development experience, they might prefer queries in code. Personally, I think having queries in code can enable developers to move much faster and security concerns can be mitigated by ensuring teams are following best practices (e.g. parameterized queries, ORM). Stored procs aren't a "silver bullet" for system security.
Does the use of procedures still make sense in 202X?
Maybe in low level and rare scenarios or if we write code for a legacy companies with unfounded restrictions, stored procedure should be an option.
If entire logic is in the database, should I need a dba to change it?
No. In modern platforms, the requirement of a DBA to change the business logic is not an option.
Hot modification of stored procedures without dev or staging phases, area a crazy idea.
How easy is to maintain a procedure with dozens of lines, cursors and other low level database features vs a OOP objects in any modern language in which a junior developer is able to maintain?
This answers itself
Hide tables from my development team for security reasons sounds very crazy for me, in these times in which agility and well documentation are everything.
Modern development team with a modern database, should not worry about security. What's more, they need access to sandbox version of database to reduce the time of its deliverables.
With modern ORMs, ESBs, ETLs and the constant increase of cpu power, stored procedures are not an option anymore. Should I invest time and money in these tools, to create at final: one big stored procedure?
Of course, not.
On top of the speed and security considerations, I tend to stick as much in Stored Procedures as possible for ease of maintenance and alterations. If you put the logic in your application, and find later that sql logic has an error or needs to work differently in some manner, you have to recompile and redeploy the whole app in many cases (especially if it's a client side app such as WPF, Win-Forms, etc). If you keep the logic in the stored proc, all you have to do is update the proc and you never have to touch the application.
I agree that they should be used often and well.
The use case I think is extremely compelling and extremely useful is if you are taking in a lot of raw information that should be separated out into several tables, where the some of the data may have records that already exist and need to be connected by foreign key id, then you can just IF EXISTS checks and insert if it doesn't or return key if it does, which makes everything more uniform, succinct, and maintainable in the long run.
The only case where I would suggest against using them is if you are doing a lot of logic or number crunching between queries which is best done in the app server OR if you are working for a company where keeping all of the logic in the code is important for maintainability/understanding what is happening. If you have a git repository full of everything anyone would need and is easily understandable, that can be very valuable.
The stored procedures are a method of collecting operations that should be done together on database side, while still keeping them on database side.
This includes:
Populating several tables from one rowsource
Checking several tables against different business rules
Performing operations that cannot be efficiently performed using set-based approach
etc.
The main problem with stored procedures is that they are hard to maintain.
You, therefore, should make stored procedures as easy to maintain as all your other code.
I have an article on this in my blog:
Schema junk
I've had some very bad experiences with this.
I'm not opposed to stored procedures in their place, but gratuitous use of stored procedures can be very expensive.
First, stored procedures run on the database server. That means that if you have a multi-server environment with 50 webservers and one database server, instead of spreading workloads over 50 cheap machines, you load up one expensive one (since the database server is commonly built as a heavyweight server). And you're risking creating a single-point-of-failure.
Secondly, it's not very easy to write an application solely in stored procedures, although I ran into one that made a superhuman effort to try to. So you end up with something that's expensive to maintain: It's implemented in 2 different programming languages, and the source code is often not all in one place either, since stored procedures are definitively stored in the DBMS and not in a source archive. Assuming that someone ever managed/bothered o pull them out of the database server and source-archive them at all.
So aside from a fairly messy app architecture, you also limit the set of qualified chimpanzees who can maintain it, as multiple skills are required.
On the other hand, stored procedures are extremely useful, IF:
You need to maintain some sort of data integrity across multiple systems. That is, the stored logic doesn't belong to any single app, but you need consistent behavior from all participating apps. A certain amount of this is almost inevitable in modern-day apps in the form of foreign keys and triggers, but occasionally, major editing and validation may be warranted as well.
You need performance that can only be achieved by running logic on the database server itself and not as a client. But, as I said, when you do that, you're eating into the total system resources of the DBMS server. So it behooves you to ensure that if there are significant bits of the offending operation that CAN be offloaded onto clients, you can separate them out and leave the most critical stuff for the DBMS server.
A particular scenario you're likely to benefit involves the situation around the "(n+1)" scalability problem. Any kind of multidimensional/hierarchical situation is likely to involve this scenario.
Another scenario would involve use cases where it does some protocol when handling the tables (hint: defined steps which transactions are likely to be involved), this could benefit from locality of reference: Being in the server, queries might benefit. OTOH, you could supply a batch of statements directly into the server. Specially when you're on a XA environment and you have to access federated databases.
If you are talking business logic rather than just "Should I use sprocs in general" I would say you should put business logic in sprocs when you are carrying out large set based operations or any other time executing the logic would require a large number of calls to the db from the app.
It also depends on your audience. Is ease of installation and portability across DBMSs important to you?
If your program should be easy to install and easy to run on different database systems then you should stay away from stored procedures and also look out for non-portable SQL in your code.

Where should database queries live?

Should queries live inside the classes that need the data? Should queries live in stored procedures in the database so that they are reusable?
In the first situation, changing your queries won't affect other people (either other code or people generating reports, etc). In the second, the queries are reusable by many and only exist in one place, but if someone breaks them, they're broken for everyone.
I used to be big on the stored proc solution but have changed my tune in the last year as databases have gotten faster and ORMs have entered the main stream. There is certainly a place for stored procs. But when it comes to simple CRUD sql: one liner insert/update/select/delete, using an ORM to handle this is the most elegant solution in my opinion, but I'm sure many will argue the other way. An ORM will take the SQL and DB connection building plumbing out of your code and make the persistence logic much more fluidly integrated with your app.
I suggest placing them as stored procedures in the database. Not only will you have the re-use advantage but also you'll make sure the same query (being a select, update, insert, etc...) it is the same because you are using the same stored procedure. If you need to change it, you'll only change it in one place. Also, you'll be taking advantage of the database server's processing power instead of the server/computer where your application resides. That is my suggestion.
Good luck!
It depends / it's situational. There are very strong arguments for and against either option. Personally, I really don't like seeing business logic get split between the database (in stored procedures) and in code, so I usually want all the queries in code to the maximum extent possible.
In the Microsoft world, there are things like Reporting Services that can retrieve data from classes/objects instead of (and in addition to) a database / stored procedures. Also, there are things like Linq that give you more strongly typed queries in code. There are also strong, mature ORMs like NHibernate that allow for writing pretty much all types of queries from code.
That said, there are still times when you are doing "rowset" types of things with your queries that work much better in a stored procedure than they work from code.
In the majority of situations, either/both options work just fine.
From my perspective, I think that stored procs are the the way to go. First, they are easier to maintain as a quick change to one means just running the script not recompiling the application. Second they are far better for security. You can set permissions at the sp level and not directly on the tables and views. This helps prevent fraud because the users cannot do anything directly to the datbase that isn't specified in a stored proc. They are easier to performance tune. When you use stored procs, you can use the database dependency metadata to help determine the affect of database changes on the code base. In many systems, not all data access or or even CRUD operations will take place through the application, having the code there seems to me to be counterproductive. If all the data access is in one place (an idea I support), it should be in the database where it is accessible to all applications or processes that might need to use it.
I've found that application programmers often don't consider the best way for a database to process information as they are focused on the application not the backend. By putting the code for the database in the database where it belongs, it is more likely to be seen and reviewed by database specialists who do consider the database and it's perfomance. We support hundreds of databases and applications here. I can look in any database and find the code that I need to find when something is slow. I don't have to upload the application code for each of hundreds of different applications just to see the part I need to do my job.

How do I 'refactor' SQL Queries?

I have several MS Access queries (in views and stored procedures) that I am converting to SQL Server 2000 (T-SQL). Due to Access's limitations regarding sub-queries, and or the limitations of the original developer, many views have been created that function only as sub-queries for other views.
I don't have a clear business requirements spec, except to 'do what the Access application does', and half a page of notes on reports/CSV extracts, but the Access application doesn't even do what I suspect is required properly.
I, therefore, have to take a bottom up approach, and 'copy' the Access DB to T-SQL, where I would normally have a better understanding of requirements and take a top down approach, creating new queries to satisfy well defined requirements.
Is there a method I can follow in doing this? Do I spread it all out and spend a few days 'grokking' it, or do I continue just copying the Access views and adopt an evolutionary approach to optimising the querying?
Work out what access does with the queries, and then use this knowledge to check that you've transferred it properly. Only once you've done this can you think about refactoring. I'd start with slow queries and then go from there: work out what indexes you need and then progressively rewrite. This way you can deliver as soon as you've proved that you moved everything successfully (even if it is potentially a bit slower). That's much better than not being able to deliver at all because problem X came along.
I'd probably start with the Access database, exercise the queries in situ and see what the resultset is. Often you can understand what the query accomplishes and then work back to your own design to accomplish it. (To be thorough, you'll need to understand the intent pretty completely anyway.) And that sounds like the best statement of requirements you're going to get - "Just like it's implemented now."
Other than that, You're approach is the best I can think of. Once they are in SQL Server, just start testing and grokking.
When you are dealing with a problem like this it's often helpful to keep things working as they are while you make incremental changes. This is better from a risk management perspective.
I'd concentrate on getting it working, then checking the database performance and optimizing performance problems. Then, as you add features and fix bugs, clean up the code that's hard to maintain. As you said, a sub-query is really very similar to a view. So if it's not broken you may not need to change it.
This depends on your timeline. If you have to get the project running absolutely as soon as possible (I know this is true for EVERY project, but if it's REALLY true for you), then yes, duplicate the functionality and infrastructure from Access then do your refactoring either later or as you go.
If you have SOME time you can dedicate to it, then refactoring it now will give you two things:
You'll be happier with the code, and it will (likely) perform better, since actual analysis was done rather than the transcoding equivalent of a copy-paste
You'll likely gain a greater understanding of what the true business rules are, since you'll almost certainly come across things that aren't in the spec (especially considering how you describe them)
I would recommend copying the views to SQL Server immediately, and then use its sophisticated tools to help you grok them.
For example, SQL Server can tell you what views, stored procedures, etc, rely on a particular view, so you can see from there whether the view is a one-of or if it's actually used in more than one place. It will help you determine which views are more important than which.

Can you have too many stored procedures?

Is there such a thing as too many stored procedures?
I know there is not a limit to the number you can have but is this any performance or architectural reason not to create hundreds, thousands??
To me the biggest limitation to that hundreds or thousands store procedure is maintainability. Even though that is not a direct performance hit, it should be a consideration. That is an architectural stand point, you have to plan not just for the initial development of the application, but future changes and maintenance.
That being said you should design/create as many as your application requires. Although with Hibernate, NHibernate, .NET LINQ I would try to keep as much store procedures logic in the code, and only put it in the database when speed is a factor.
Yes you can.
If you have more than zero, you have too many
Do you mean besides the fact that you have to maintain all of them when you make a change to the database? That's the big reason for me. It's better to have fewer ones that can handle many scenarios than hundreds that can only handle one.
I would just mention that with all such things maintenance becomes an issue. Who knows what they all are and what purpose they serve? What happens years down the way when they are just artifacts of a legacy system that no one can recall what they are for but are scared to mess with?
I think the main thing is the question of not is it possible, but should it be done. Thats just one thought anyway.
I have just under 200 in a commercial SQL Server 2005 product of mine, which is likely to increase by about another 10-20 in the next few days for some new reports.
Where possible I write 'subroutine' sprocs, so that anytime I find myself putting 3 or 4 identical statements together in more than a couple of sprocs, it's time to turn those few statements into a subroutine, if you see what I mean.
I don't tend to use the sprocs to perform all the business logic as such, I just prefer to have sprocs doing anything that could be seen as 'transactional' - so where as my client code (in Delphi but whatever) might do the odd insert or update itself, as soon as something requires a couple of things to be updated or inserted 'at once', it's time for a sproc.
I have a simple, crude naming convention to assist in the readability (and in maintenance!)
The product's code name is 'Rachel', so we have
RP_whatever - these are general sprocs that update/insert data,
- or return small result sets
RXP_whatever - these are subroutine sprocs that server as 'functions'
- or workers to the RP_ type procs
REP_whatever - these are sprocs that simply act as glorified views almost
- they don't alter data, they return potentially complex result sets
- for reporting purposes, etc
XX_whatever - these are internal test/development/maintenance sprocs
- that the client application (or the local dba) would not normally use
the naming is arbitrary, it's just to help distinguish from the sp_ prefix that SQL Server uses.
I guess if I found I had 400-500 sprocs in the database I might become concerned, but a few hundred isn't a problem at all as long as you have a system for identifying what kind of activity each sproc is responsible for. I'd rather chase down schema changes in a few hundred sprocs (where the SQL Server tools can help you find dependencies etc) than try to chase down schema changes in my high-level programming language.
I suppose the deeper question here is- where else should all of that code go? Views can be used to provide convenient access to data through standard SQL. More powerful application languages and libraries can be used to generate SQL. Stored procedures tend to obscure the nature of the data and introduce an unnecessary layer of abstraction, complexity, and maintenance to a system.
Given the power of object relational mapping tools to generate basic SQL, any system that is overly dependent on stored procedures is going to be less efficient to develop. With ORM, there is simply a lot less code to write.
Hell yes, you can have too many. I worked on a system a couple of year ago that had something like 10,000 procs. It was insane. The people who wrote the system didn't really know how to program but they did know how to right badly structured procs, so they put almost all of the application logic in the procs. Some of the procs ran for thousands of line. Managing the mess was a nightmare.
Too many (and I can't draw you a specific line in the sand) is probably an indicator of poor design. Besides, as others have pointed out, there are better ways to achieve a granular database interface without resorting to massive numbers of procs.
My question is why aren't you using some sort of middleware platform if you're talking about hundreds or thousands of stored procedures?
Call me old fashioned but I thought the database should just hold the data and the program(s) should be the one making the business logic decisions.
in Oracle database you can use Packages to group related procedures together.
a few of those and your namespace would free up.
Too much of any particular thing probably means you're doing it wrong. Too many config files, too many buttns on the screen ...
Can't speak for other RDBMSs but an Oracle application that uses PL/SQL should be logically bundling procedures and functions into packages to prevent cascading invalidations and manage code better.
To me, using lots of stored procedures seems to lead you toward something equivalent to the PHP API. Thousands of global functions which may have nothing to do with eachother all grouped together. The only way to relate between them is to have some naming convention where you prefix each function with a module name, similar to the mysql_ functions in PHP. I think this is very hard to maintain, and very hard to to keep everything consistent. I think stored procedures work well for things that really need to take place on the server. A stored procedure for a simple select query, or even a select query with a join is probably going to far. Only use stored procedures where you actually require advanced logic to be handled on the database server.
As others have said, it really comes down to the management aspect. After a while, it turns into finding the proverbial needle in the haystack. That's even more so when there's poor naming standards in place...
No, not that I know of. However, you should have a good naming convention for them. For example, starting them with usp_ is something that a lot of poeple like to do (fastr than starting with sp_).
Maybe your reporting sprocs should be usp_reporting_, and your bussiness objects should be usp_bussiness_, etc. As long s you can manage them, there shouldn't be a problem with having a lot of them.
If they get too big you might want to split the database up into multiple databases. This might make more logical sense and can help with database size and such.
Yep, you can have toooooo many stored procedures.
Naming conventions can really help with this. For instance, if you have a naming convention where you always have the table name and InsUpd or Get, it's pretty easy to find the right stored procedure when you need it. If you don't have some kind of standard naming convention it would be really easy to come up with two (or more) procedures that do almost exactly the same thing.
It would be easy to find a couple of the following without having a standardized naming convention... usp_GetCustomersOrder, CustomerOrderGet_sp, GetOrdersByCustomer_sp, spOrderDetailFetch, GetCustOrderInfo, etc.
Another thing that starts happening when you have a lot of stored procedures is that you'll have some stored procedures that are never used and some that are just rarely used... If you don't have some way of tracking stored procedure usage you'll either end up with a lot of unused procedures... or worse, getting rid of one you think is never used and finding out afterwards that it's only used once a year or once a quarter. :(
Jeff
Not while you have sane naming conventions, up-to-date documentation and enough unit tests to keep them organized.
My first big project was developed with an Object Relational Mapper that abstracted the database so we did everything object oriented and it was easier to mantain and fix bugs and it was especially easy to make changes since all the data access and business logic was C# code, however, when it came to do complex stuff the system felt slow so we had to work around those things or re-architect the project, especially when the ORM had to do complex joins in the database.
Im now working on a different company that has a motto of "our applications are just frontends of the database" and it has its advantages and disadvantages. We have really fast applications since all of the data operations are done on stored procedures, this is using mainly SQL Server 2005, but, when it comes to make a change, or a fix to the software its harder because you have to change both, the C# code and the SQL stored procedures so its like working twice, contrary to when I used an ORM, you dont have refactoring or strongly typed objects in sql, Management Studio and other tools help a lot but normally you spend more time going this way.
So I would say that deppending on the needs of the project, if you are not going to keep really complex business data than maybe you could even avoid using stored procedures at all and use an ORM that makes developer life's easier. If you are concerned about performance and need to save all of the resources than you should use stored procedures, of course, the quantity deppends uppon the architecture that you design, so for exmaple if you always have stored procedures for CRUD operations you would need one for inserts, one for update, one for deletion, one for selecting and one for listing since these are the most common operations, if you have 100 business objects, multiply these 4 by that and you get 400 stored procedures just to manage the most basic operations on your objects so, yes, they could be too many.
If you have a lot of stored procedures, you'll find you are tying yourself to one database - some of them may not easily be transferred.
Tying yourself to one database isn't good design.
Moreover, if you have business logic on the database and in a business layer then maintenance becomes a problem.
i think as long as you name them uspXXX and not spXXX the lookup by name will be direct, so no downside - though you might wonder about generalizing the procs if you have thousands...
You have to put all that code somewhere.
If you are going to have stored procedures at all (I personally do favour them, but many do not), then you might as well use them as much as you need to. At least all the database logic is in one place. The downside is that there isn't typically much structure to a bucket full of stored procs.
Your call! :)

Which is better: Ad hoc queries or stored procedures? [closed]

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Assuming you can't use LINQ for whatever reason, is it a better practice to place your queries in stored procedures, or is it just as good a practice to execute ad hoc queries against the database (say, SQL Server for argument's sake)?
In my experience writing mostly WinForms Client/Server apps these are the simple conclusions I've come to:
Use Stored Procedures:
For any complex data work. If you're going to be doing something truly requiring a cursor or temp tables it's usually fastest to do it within SQL Server.
When you need to lock down access to the data. If you don't give table access to users (or role or whatever) you can be sure that the only way to interact with the data is through the SP's you create.
Use ad-hoc queries:
For CRUD when you don't need to restrict data access (or are doing so in another manner).
For simple searches. Creating SP's for a bunch of search criteria is a pain and difficult to maintain. If you can generate a reasonably fast search query use that.
In most of my applications I've used both SP's and ad-hoc sql, though I find I'm using SP's less and less as they end up being code just like C#, only harder to version control, test, and maintain. I would recommend using ad-hoc sql unless you can find a specific reason not to.
I can't speak to anything other than SQL Server, but the performance argument is not significantly valid there unless you're on 6.5 or earlier. SQL Server has been caching ad-hoc execution plans for roughly a decade now.
I think this is a basic conflict between people who must maintain the database and people who develop the user interfaces.
As a data person, I would not consider working with a database that is accessed through adhoc queries because they are difficult to effectively tune or manage. How can I know what affect a change to the schema will have? Additionally, I do not think users should ever be granted direct access to the database tables for security reasons (and I do not just mean SQL injection attacks, but also because it is a basic internal control to not allow direct rights and require all users to use only the procs designed for the app. This is to prevent possible fraud. Any financial system which allows direct insert, update or delete rights to tables is has a huge risk for fraud. This is a bad thing.).
Databases are not object-oriented and code which seems good from an object-oriented perspective is can be extremely bad from a database perspective.
Our developers tell us they are glad that all our databse access is through procs becasue it makes it much faster to fix a data-centered bug and then simply run the proc on the production environment rather than create a new branch of the code and recompile and reload to production. We require all our procs to be in subversion, so source control is not an issue at all. If it isn't in Subversion, it will periodically get dropped by the dbas, so there is no resistance to using Source Control.
Stored procedures represent a software contract that encapsulates the actions taken against the database. The code in the procedures, and even the schema of the database itself can be changed without affecting compiled, deployed code, just so the inputs and outputs of the procedure remain the same.
By embedding queries in your application, you are tightly coupling yourself to your data model.
For the same reason, it is also not good practice to simply create stored procedures that are just CRUD queries against every table in your database, since this is still tight coupling. The procedures should instead be bulky, coarse grained operations.
From a security perspective, it is good practice to disallow db_datareader and db_datawriter from your application and only allow access to stored procedures.
Stored procedures are definitely the way to go...they are compiled, have execution plan before hand and you could do rights management on them.
I do not understand this whole source control issue on stored procedure. You definitely can source control them, if only you are a little disciplined.
Always start with a .sql file that is the source of your stored procedure. Put it in version control once you have written your code. The next time you want to edit your stored procedure get it from your source control than your database. If you follow this, you will have as good source control as your code.
I would like to quote Tom Kyte from Oracle here...Here's his rule on where to write code...though a bit unrelated but good to know I guess.
Start with stored procedures in PL/SQL...
If you think something can't be done using stored procedure in PL/SQL, use Java stored procedure.
If you think something can't be done using Java Stored procedure, consider Pro*c.
If you think you can't achieve something using Pro*C, you might want to rethink what you need to get done.
My answer from a different post:
Stored Procedures are MORE maintainable because:
You don't have to recompile your C# app whenever you want to change some SQL
You end up reusing SQL code.
Code repetition is the worst thing you can do when you're trying to build a maintainable application!
What happens when you find a logic error that needs to be corrected in multiple places? You're more apt to forget to change that last spot where you copy & pasted your code.
In my opinion, the performance & security gains are an added plus. You can still write insecure/inefficient SQL stored procedures.
Easier to port to another DB - no procs to port
It's not very hard to script out all your stored procedures for creation in another DB. In fact - it's easier than exporting your tables because there are no primary/foreign keys to worry about.
In our application, there is a layer of code that provides the content of the query (and is sometimes a call to a stored procedure). This allows us to:
easily have all the queries under version control
to make what ever changes are required to each query for different database servers
eliminates repetition of the same query code through out our code
Access control is implemented in the middle layer, rather than in the database, so we don't need stored procedures there. This is in some ways a middle road between ad hoc queries and stored procs.
There are persuasive arguments for both - stored procedures are all located in a central repository, but are (potentially) hard to migrate and ad hoc queries are easier to debug as they are with your code, but they can also be harder to find in the code.
The argument that stored procedures are more efficient doesn't hold water anymore.
link text
Doing a google for Stored Procedure vs Dynamic Query will show decent arguments either way and probably best for you to make your own decision...
Store procedures should be used as much as possible, if your writing SQL into code your already setting yourself up for headaches in the futures. It takes about the same time to write a SPROC as it does to write it in code.
Consider a query that runs great under a medium load but once it goes into fulltime production your badly optimized query hammers the system and brings it to a crawl. In most SQL servers you are not the only application/service that is using it. Your application has now brought a bunch of angry people at your door.
If you have your queries in SPROCs you also allow your friendly DBA to manage and optimize with out recompiling or breaking your app. Remember DBA's are experts in this field, they know what to do and not do. It makes sense to utilise their greater knowledge!
EDIT: someone said that recompile is a lazy excuse! yeah lets see how lazy you feel when you have to recompile and deploy your app to 1000's of desktops, all because the DBA has told you that your ad-hoc Query is eating up too much Server time!
someone said that recompile is a lazy excuse! yeah lets see how lazy you feel when you have to recompile and deploy your app to 1000's of desktops, all because the DBA has told you that your ad-hoc Query is eating up too much Server time!
is it good system architecture if you let connect 1000 desktops directly to database?
Some things to think about here: Who Needs Stored Procedures, Anyways?
Clearly it's a matter of your own needs and preferences, but one very important thing to think about when using ad hoc queries in a public-facing environment is security. Always parameterize them and watch out for the typical vulnerabilities like SQL-injection attacks.
Stored Procedures are great because they can be changed without a recompile. I would try to use them as often as possible.
I only use ad-hoc for queries that are dynamically generated based on user input.
Procs for the reasons mentioned by others and also it is easier to tune a proc with profiler or parts of a proc. This way you don't have to tell someone to run his app to find out what is being sent to SQL server
If you do use ad-hoc queries make sure that they are parameterized
Parametized SQL or SPROC...doesn't matter from a performance stand point...you can query optimize either one.
For me the last remaining benefit of a SPROC is that I can eliminate a lot SQL rights management by only granting my login rights to execute sprocs...if you use Parametized SQL the login withing your connection string has a lot more rights (writing ANY kind of select statement on one of the tables they have access too for example).
I still prefer Parametized SQL though...
I haven't found any compelling argument for using ad-hoc queries. Especially those mixed up with your C#/Java/PHP code.
The sproc performance argument is moot - the 3 top RDBMs use query plan caching and have been for awhile. Its been documented... Or is 1995 still?
However, embedding SQL in your app is a terrible design too - code maintenance seems to be a missing concept for many.
If an application can start from scratch with an ORM (greenfield applications are far and few between!) its a great choice as your class model drives your DB model - and saves LOTS of time.
If an ORM framework is not available we have taken a hybrid of approach of creating an SQL resource XML file to look up SQL strings as we need them (they are then cached by the resource framework). If the SQL needs any minor manipulation its done in code - if major SQL string manipulation is needed we rethink the approach.
This hybrid approach lends to easy management by the developers (maybe we are the minority as my team is bright enough to read a query plan) and deployment is a simple checkout from SVN. Also, it makes switching RDBMs easier - just swap out the SQL resource file (not as easy as an ORM tool of course, but connecting to legacy systems or non-supported database this works)
Depends what your goal is. If you want to retrieve a list of items and it happens once during your application's entire run for example, it's probably not worth the effort of using a stored procedure. On the other hand, a query that runs repeatedly and takes a (relatively) long time to execute is an excellent candidate for database storage, since the performance will be better.
If your application lives almost entirely within the database, stored procedures are a no-brainer. If you're writing a desktop application to which the database is only tangentially important, ad-hoc queries may be a better option, as it keeps all of your code in one place.
#Terrapin: I think your assertion that the fact that you don't have to recompile your app to make modifications makes stored procedures a better option is a non-starter. There may be reasons to choose stored procedures over ad-hoc queries, but in the absence of anything else compelling, the compile issue seems like laziness rather than a real reason.
My experience is that 90% of queries and/or stored procedures should not be written at all (at least by hand).
Data access should be generated somehow automaticly. You can decide if you'd like to staticly generate procedures in compile time or dynamically at run time but when you want add column to the table (property to the object) you should modify only one file.
I prefer keeping all data access logic in the program code, in which the data access layer executes straight SQL queries. On the other hand, data management logic I put in the database in the form of triggers, stored procedures, custom functions and whatnot. An example of something I deem worthy of database-ifying is data generation - assume our customer has a FirstName and a LastName. Now, the user interface needs a DisplayName, which is derived from some nontrivial logic. For this generation, I create a stored procedure which is then executed by a trigger whenever the row (or other source data) is updated.
There appears to be this somewhat common misunderstanding that the data access layer IS the database and everything about data and data access goes in there "just because". This is simply wrong but I see a lot of designs which derive from this idea. Perhaps this is a local phenomonon, though.
I may just be turned off the idea of SPs after seeing so many badly designed ones. For example, one project I participated in used a set of CRUD stored procedures for every table and every possible query they encountered. In doing so they simply added another completely pointless layer. It is painful to even think about such things.
These days I hardly ever use stored procedures. I only use them for complicated sql queries that can't easily be done in code.
One of the main reasons is because stored procedures do not work as well with OR mappers.
These days I think you need a very good reason to write a business application / information system that does not use some sort of OR mapper.
Stored procedure work as block of code so in place of adhoc query it work fast.
Another thing is stored procedure give recompile option which the best part of
SQL you just use this for stored procedures nothing like this in adhoc query.
Some result in query and stored procedure are different that's my personal exp.
Use cast and covert function for check this.
Must use stored procedure for big projects to improve the performance.
I had 420 procedures in my project and it's work fine for me. I work for last 3 years on this project.
So use only procedures for any transaction.
is it good system architecture if you
let connect 1000 desktops directly to
database?
No it's obviously not, it's maybe a poor example but I think the point I was trying to make is clear, your DBA looks after your database infrastructure this is were their expertise is, stuffing SQL in code locks the door to them and their expertise.