[benkant]

This is good work and if I ever did web development, it would be like this. Why people in the web world don't use stored procedures and constraints is a mystery to me. That this approach is seen as novel is in itself fascinating.

It's like all those web framework inventors didn't read past chapter 2 of their database manuals. So they wrote a whole pile of code that forces you to add semantics in another language elsewhere in your code in a language that makes impedance stark. PostgreSQL is advanced technology. Whatever you might consider doing in your CRUD software, PostgreSQL has a neat solution. You can extend SQL, add new types, use PL/SQL in a bunch of different languages, background workers, triggers, constraints, permissions. Obviously there are limits but you don't reinvent web servers because Apache doesn't transcode video on the fly. Well, you do if you're whoever makes Rubby on Rails.

The argument that you don't want to write any code that locks you to a database is some stunning lack of awareness, as you decide to lock yourself into the tsunami of unpredictability that is web frameworks to ward off the evil of being locked into a 20 year database product built on some pretty sound theoretical foundations.

Web developers really took the whole "let's make more work for ourselves" idea and ran with it all the way to the bank.

You'd have to pay me a million dollars a year to do web development.

[3pt14159]

You are speaking from ignorance with the voice of authority.

I worked on a rails app that handled a billion requests per day. The problem isn't performance of the web framework, those are easy to load balance and split into C or cache when you need it. The problem is scaling your database, keeping your data secure, and iterating to meet business goals with a growing codebase and infrastructure. A mess of stored procedures would restrain you from doing all three.

And I know, I worked on a codebase in 1999 that did this because of the "performance gains". It ended up bricking the project due to inability to iterate.

[sergiosgc]

> The problem is scaling your database, keeping your data secure, and iterating to meet business goals with a growing codebase and infrastructure. A mess of stored procedures would restrain you from doing all three.

Your argument has a non sequitur right here. A mess of [foo] is a mess; the layer it is in does not matter; the language it is in does not matter. A mess of application layer code is equally effective in preventing scale, security and effectiveness.

The original post is right. Web developers treat their databases poorly[1]. A database is an interface to your data that maintains integrity. Maintaining integrity almost always means stored procedures, as some validation is not expressible as relational integrity and basic type validation.

Now, if you are at the point where your database fully guarantees integrity of data going in and coming out, a REST interface is a small step away. This project is very welcome.

[1] The typical web developer treats a database as a data store. It is also a data store, but a well designed database is much more than than.

[bkeroack]

A mess is a mess, true, but some are easier to clean up than others.

GP is correct. Methods for scaling/optimizing the application layer are clear and well-known. Scaling the data layer is a huge challenge. This is why the market is filled with snake oil databases promising linear scalability and perfect consistency/reliability, etc.

[threeseed]

Scaling the data layer is a huge challenge. No doubt. But calling databases that are designed for solving these problems "snake oil" undermines the huge amount of work that serious engineers have invested in this. No one has ever promised linear scalability and perfect consistency/reliability. No one.

Cassandra, HBase, CouchDB etc even MongoDB have built in scalability as a first order priority from day one and have been largely successful at it e.g. iCloud, EA Online, PSN. Databases like this are a nightmare to work with for smaller datasets but work incredibly well with larger ones.

It's always a shame to see HN act like you scale vertically and magically every problem is solved.

[AlisdairO]

> It's always a shame to see HN act like you scale vertically and magically every problem is solved.

When this is seen (and IME it's a pretty minority opinion) I think it's there as a reaction to the massive overuse and hype regarding a lot of newer-gen DBs. There's absolutely no doubt that there are good uses for them, but those cases are pretty niche compared to the level of their uptake.

[volaski]

You should read "innovator's dilemma"

[fweespeech]

MongoDB heavily implied the linear scalability, consistency, reliability bit in its early material [particularly in their marketing].

Its only in the past couple years they really started mentioning the fact it was "tunable consistency" blatantly rather rather than burying it in a couple places in the manual.

[3pt14159]

I purposely chose a non sequitur in the interests of speeding up the prose. It is an acceptable method frequently utilized in language. It roughly translates to:

"Than (what will certainly be given the expressiveness and level of abstraction they provide) a mess of stored procedures."

[tomchristie]

"The problem is scaling your database, keeping your data secure, and iterating to meet business goals with a growing codebase and infrastructure. A mess of stored procedures would restrain you from doing all three."

Perfectly expressed.

[e12e]

I'm always a little confused that people seem desperate to use the wrong tool, and then blame the tool. If you need to store normalized data and maintain integrety -- you'll end up with the equivalent of an SQL datastore (or, more likely a system that is faster, but subtly broken).

Sure, it's difficult to scale ACID. But if what you need is a way to serialize objects, you'll probably be better off with something like Gemstone/GLASS, a document store or some other kind of object database?

If your problem domain actually fits working with structured data, then using an SQL system makes a lot of sense. The obvious example for "web scale" here is Stackoverflow. Sure their architecture has grown a little since it was 2xIIS+2xSQL Server -- but they got pretty far on just that.

[brightball]

The bigger issue is this idea that everything needs to live in one place. For the bulk of an application handling a billion requests / day I'd wager that most of that traffic is isolated to certain types of data.

I'd wager that because in almost every case I've ever seen it's true. You just don't tend to see every table in a normalized dataset bearing the traffic load.

If that is the case, rolling that particular piece of data out to a more easily scalable store will largely fix the problem, if caching, async writes and buffered writes didn't already.

Everything else can very easily sit in PostgreSQL, avoid race conditions, maintain data integrity, have permissions controlled and be accessed from multiple languages directly without requiring an API layer. Then you can use a foreign data wrapper to let PG query that other data source (mongo, couchbase, redis, whatever) and join the results with the other data in the database just like it's all one bit happy dataset.

As another poster said, a mess is a mess and honestly I don't know why he takes a shot at Rails since Rails has some of the best first class support for leveraging PostgreSQL features these days.

Wrote an entire post about it: http://www.brightball.com/ruby-postgresql/rails-gems-to-unlo...

[batou]

We are exactly there. We're having to remove vast swathes of stored procedures and rewrite everything.

[snarfy]

> The problem is scaling your database

There is only one database for everything in the business? Of course it doesn't scale. The problem you describe stems from solving every business request by adding yet another table to 'the' database.

It's a monolithic solution. It doesn't matter if you use database features or not. There is no difference between a mess of stored procedures and a mess of business logic classes. It's still a mess.

[_yy]

Web servers usually scale better than (traditional) databases, so it makes sense to not offload computation to the database, even if it means that there's an overhead.

[brightball]

That's very situational. Read scaling a database is easy. Write scaling a database is harder and doing computational logic while write scaling a database is harder still. Computational is still a very broad word though and the intensity of those computations is a huge defining factor.

The problem boils down to the "the database" idea described earlier. There are very, very few normalized datasets that I've ever seen that have write scaling concerns on more than 1 or two tables.

Move those to a separate datastore that is built for it and you've largely solved your problem. Postgres can even connect to outside datastores to run queries against them for sake of reporting.

[scottschulthess]

Web server codebases are typically also way easier to modify, unit test, with better tools and languages.

[qaqy]

there is even pl\brainfuck so as far as choice of langs PG has you covered

[rapind]

Once you get rid of your N+1s the bottleneck in my experience (working with Rails now since v1.2) has always be Rails / Ruby itself. It is so incredibly slow, even using just Metal (even Sinatra for that matter). The slowdown at the view level is significant.

I always have a caching strategy (usually varnish in front of nginx) with Rails unless it's literally only supporting a handful of users, and anytime I need to support non-cacheable hits like writes to more than 50 or so concurrents I consider swapping in Node or Go or something reasonably performant to handle just those writes.

Lately I've been looking into Elixir as a Rails alternative for APIs for performance and scalability. I am very intrigued by a PostgreSQL based REST API.

[3pt14159]

The point is that when Rails gets too slow it is very easy to switch to something like cacheing or C (Or Go, or whatever). Even if you just split it off at nginx or use a worker pool in a faster language. Or if you need lots of concurrency use Go. Or even replace the Ruby code with one fairly nasty SQL statement or a single stored procedure.

The other 95% of your code can be slow Rails. You know those pages where a user adds another email address, or where they report a comment as being hateful, or where they select what language they want the app to be in, or where you have your teams page, or your business partners page, or your API docs and key registration / invalidation.

The database doesn't scale without pain though. You have joins, you're going to need to get rid of them. You have one table on a machine, you're going to need to split it. You have speedy reliable writes, you are going to have to either make due with inconsistency and possibly have a whole strategy to clean up the data after the fact or lose the speediness.

I'm intrigued about shuffling the serialization of JSON to Postgres, but that is different than what the OP was talking about.

[brightball]

By the same logic though, at the point that heavy write load becomes a reality it's just as feasible to move the heavy write table to an isolated datastore and leave 95% of your data (structurally) in the PG. Even use a PG foreign data wrapper to connect to that new datastore to allow PG to continue any necessary queries against it.

I'm not ever going to argue for heavy stored procedure usage but there are definitely times when it makes sense and more times still when using the features in your database instead of setting up multiple different standalone systems for pubsub, search, json data, etc when your database can do it all makes sense.

It's very similar to the "you can always switch the slow parts" point with Rails to move a part to Go. You can do it all in PostgreSQL and then when you actually reach a point where you've grown it into a bottleneck, move it out.

Postgres isn't SQL Server and it isn't Oracle and it isn't MySQL. It's Postgres. It's a tool that you choose because of it fits your needs, not because somebody told you it was a good database. You choose it as part of your stack. If you are using PostgreSQL because you wanted a dumb datastore then you chose the wrong database and should probably reavaluate your options. That's like getting a Lamborghini to make grocery runs.

http://www.brightball.com/postgresql/why-should-you-learn-po...

[vkjv]

I am a postgresql novice, but I've used the JSON serialization and it is indeed fast. But, here's my question:

When you do a 1-to-many join and return the same fields very many times, do the binary drivers optimize that or is it return many times? With JSON serialization (or serializing to arrays), you only get the one row.

[wslh]

If Facebook uses MySQL and PHP there is some truth in the comment.

[jeletonskelly]

To say that Facebook uses PHP and MySQL is to leave out the truth, honestly. They are a part of the stack, yes, but they aren't what makes the application scale to billions of requests. It would be like saying the local coffee shops website using Wordpress with a MySQL backend is using the same tech as Facebook. It's laughable.

[wslh]

They choose MySQL vs a lot of other alternatives for some reason and this reasoning can be applied to your use case.

> They are a part of the stack, yes, but they aren't what makes the application scale to billions of requests.

These are not just part of the stack, these are critical components within the stack.

[threeseed]

To say that PHP/MySQL is just a "part of Facebook's stack" is laughable.

They are the core components of Facebook. Normal people understand that the characteristics of Facebook's architecture is unique to just Facebook. They can get away with sharding/colocating data that nobody else can. The rest of us have a tonne of integrated data that requires complex joins (whether at the application or database layer).

[spacemanmatt]

They are edge components of Facebook. Just from a brief interaction with FB recruiters, I learned they use a lot of Vertica in their back-office. Please don't propose that they are using MySQL for their main business when it's only powering app nodes which are just POPs fed by their real (internal) services. Approximately speaking.

[benkant]

I never mentioned performance or scaling as reasons for using a database's features- though they might be worth considering. The fact I never said those words and it fired you up says more about your experience than mine I imagine.

[batou]

That is quite frankly horse poop.

We use stored procedures. Not by choice; this is a legacy we're stuck with. It is nothing but an unadulterated disaster of a technology regardless of what you use it for. I'm talking 45,000 stored procedures here. 2000 tables. TiB of data. 50,000 requests/second across SOAP/web/desktop etc. It's hell.

Problems with stored procedures:

1) Performance. More code running in the hard to scale-out black box. You're just hanging yourself with hardware and/or license costs in the long run.

2) Maintenance. All database objects are stateful i.e. they have to be loaded to work. The sheer complexity of managing that on top of the table state results in massive cost. Add to that tooling, version control costs as well. Have you tried merging a stored procedure in a language which has no compiler and very loose verification?

3) Orthoganality. Nothing inside the relational model matches the logical concepts in your application. Think of transactions, domain modelling etc.

4) Duplication. You still have to write something in the application to talk to every single one of those stored procedures and map it to and from parameters and back to collections.

5) Transaction scoping. Do you know how expensive it is to introduce distributed transactions? Well it's a ton more cash when EVERYTHING is inside that black box.

6) Lock in. Your stored procedures aren't portable. Good luck trying to shift vendor in the future when you hit a brick wall.

Now I know it's popular to bash on Rails and I wouldn't use it personally but there are people using the same model on top of other platforms, like us.

Sorry but databases are just a hole to put your shit in when you want it out of memory. If you start investing too much in all of the specific functionality you're hanging yourself.

[kitd]

Sorry but databases are just a hole to put your shit in when you want it out of memory.

You've got to be joking, right?

Data is an enterprise's single biggest asset. A robust, consistent and performant store is vital. SPs can be written as garbage like any other logic, but in the right hands they are a perfectly valid tool for providing useful access to complex data.

[batou]

No that's about it. Granted they give you efficient paths to get it back again and store it on the right shelves but that's about it.

The key benefit is probably familiarity.

I'm not saying they're an invalid tool, merely just a single tool in a batbelt of a million solutions.

[LunaSea]

It is but NO database has the chops to help you handle the business logic.

[batou]

Despite many attempts by people to prove otherwise. Literally every "enterprise" product I've seen tried to do this and fucked it up royally.

[arethuza]

Interestingly some very enterprise products don't even try and use database features like foreign key relationships - it can be a bit of a shock to open a database with many thousands of tables and realise that there is no obvious way to work out how they relate without looking at application level structures.

[batou]

Yes that's true as well. JIRA does that in some configurations. Does my head in.

[kitd]

I'd definitely give you that. SPs are the last place you want business logic.

[benkant]

I'm sorry to hear your anecdote. I would have to come see your particular situation to see exactly what you mean by 1, 2, 5, because those don't seem unsolvable, but in general:

> 3) Orthoganality

You've introduced that by treating a relational store as a "hole to put your shit in". It's not fair to blame the database for that.

> 4) Duplication

Not with the project that is the topic of this thread you don't.

> 6) Lock in

As I mentioned in my original comment, you can be locked to your database or you can be locked to your ORM/DAO/ActiveRecord/DB client library or whatever it is you're using.

Not using database features isn't the key to heaven anymore than using them is the key to hell. I just meant to point out that in my experience they are underused massively.

[batou]

Certainly not an anedote. I was an Oracle and SQL Server DBA for a number of years amongst other hats on stupid big datasets and loads. Add to that 25 years' experience getting companies out of deep trouble that everyone else has given up on. I know my shit.

Orthogonality: I haven't introduced anything here. Very rarely does any conceptual model of reality fit into the relational model. It's more imperative than that. Everything is usually crudely shoehorned into it because it's a compromise that people are barely willing to make or because they don't understand how to model a system properly.

Duplication: there is duplication in there. The versioning is very inadequate and API stability is the key to success on this. Plus also, this is a minor part of the application to consider. It's no different to issuing SQL. The protocol is different, that is all.

Lock in: There is no ORM lock-in past the platform. If you isolate everything properly i.e. use command-query-separation then this is a non issue. It's trivial to replace the ORM. You can even do it piecemeal. We've done it. I yanked out bastardisd ADO and EF out and stuck Nhibernate in. If you couple all your logic into the database, no banana. That luxury goes out of the window.

They may be underused, but when your vendor pulls a 26% price hike on half a million quid's worth of kit, can you afford to bend over and take it?

It's a tradeoff, but not one I'm willing to make on medium to large scale systems where there is a capital risk.

[mixmastamyk]

Interesting, though as this is a way to interface with Postgres I'm not sure your warnings about licensing costs are useful. Still, there are the other reasons you mentioned.

[batou]

Some organisations won't allow use of a product unless there's a support option. I can understand this after a complete system failure a few years back on an open source unsupported product. I was hired to fix it! :) Mostly though in comes EnterpriseDB and support costs then. Problem is always staff availability here in the UK though so we always end up with SQL Server and Orscle bodies.

[threeseed]

How can you compare being locked into a DB versus locked into an ORM ?

One of the main features of an ORM has been abstraction from the intrinsic properties of that database. ORM was a concept that was popularised by the original Obj-C/EOF/WebObjects back in the day which supported retrieving data from any database you pointed it at. And it fully supported you enhancing it's access layer with database specific features.

[brightball]

This is a much longer topic but it boils down to 2 things:

1. Switching your database is not easy with or without stored procedures because it will involve down time for the application while the data is migrated, then verifying that it works as expected in the new database with that ORM. You hope for the best, but it's always more complicated to switch a database.

2. The ORM tends to lock you into the application stack. Switching a part of your application from something like Rails to Go when you need to performance tune is significantly easier and more common than switching the entire database backing the whole system.

Beyond those two are the harsh realities of working with large datasets. As soon as a dataset it non-trivially small relying on the application to do core work on it becomes self destructive by adding network latency and in many cases object creation (check some Rails benchmarks on object creation costs). It becomes a big deal.

This is not to say that doing the bulk of work in the ORM is bad or that everything should be done in the database, it's a matter of balance. The only dangerous opinions on the matter are the "purist to the detriment of all else."

Verifying uniqueness, exclusion and maintaining data integrity should be the job of the database in most cases. That is what it's good at. Performing actual business logic on that data should not unless there is a significant performance based reason for it in most cases.

In Postgres the "stored procedure" thing is a little bit different because they're significantly more valuable thanks to the volume of functionality built into PG. Everything is basically a function in PG.

In PG, you can use functions to create indexes and when the function is used in a where clause that index will be used. You can use functions to create constraints, unique indexes and even notify outside process that are listening of changes in the database with pubsub.

PG is a heck of a lot more than just a "datastore" and that's why these discussions are important. If you want a generic dumb datastore...there are databases built for that. PG is built for a whole lot more than that.

Here's a very incomplete summary: http://www.brightball.com/postgresql/why-should-you-learn-po...

[LGBT_2000]

1) Makes no sense whatsoever; stored procedures are typically going to be much faster than the equivalent mix of application-level code written in a scripting language that needs to communicate with a database and is likely vastly slower than PL/pgSQL or PL/SQL. The hardware licensing costs having nothing to do with stored procedures and apply just as much to anything else (there's free as an beer options and costly proprietary ones in either case).

2) This is not a reasonable objection, I could replace "loaded" with "compiled" and your non-argument would make just as much sense. The alternative does not make the "complexity" go away, it just distributes across multiple languages in your application and database.

3) No.

4) Another non-argument against stored procedures. For example, suppose I have a table "time_series(series_id INT, tstamp TIMESTAMP, val NUMERIC)". A common need would be to accumulate all points (tstamp, val) associated with a series_id. Following your logic, you either end up with tons of con the application side sending similar variations of a query that looks like "SELECT tstamp, val FROM time_series WHERE series_id = $x ORDER BY tstamp" or you create one application-level module that acts as an abstraction around a query like that. In the first case, you're doing massive duplication. In the second case, you've essentially made a stored procedure that is distributed across your database and application and all the issues you raised of having to write something to talk to it apply just the same.

5) Again, no. DBs are precisely to place to deal with issues like this as they have means for dealing with things like foreign tables. The application-level alternative just means re-inventing it all yourself and you're probably going to make a lot more mistakes and write a lot more code that way.

6) Non-argument (applies just as well to Rails, Python, Linux, etc.)

[spdionis]

You had me until your last sentence. Database are very important to (and very good at) store your data. And data is important (duh). All the issues you described above are related to working with the data, which should not happen in the database.

[batou]

That's a poor argument because we're not discussing the arbitraty boundary of storing versus working with data as the lines between those are very blurred. This is even more the case when you use stored procedures which work with data close to the storage.

While we're on this subject, RDBMS are no better at storing data than any other technology out there[1]. In fact when you start thinking abstractly like this, other tech such as Riak makes sense for a lot of workloads.

The only real benefits of RDBMS' are fixed schema, fungibility of staff, the ability to issue completely random queries and get a result in a reasonable amount of time and the proliferation of ORMs.

[1] Caveated on insane design decisions like MyISAM storage engine and MongoDB as a whole.

[AlisdairO]

Riak makes sense for some workloads. For the vast majority of workloads out there, you will save time and money with an ACID system. Good ACID systems are mostly RDBMSs, so I would say, for now at least, that typical RDBMSs do have a leg up on other technologies out there.

[batou]

Definitely. Which is why we still use one. It's cheap, already there and does the job.

[jakub_h]

It seems to me that least in a part of you argument, you seem to be confusing the deficiencies of particular implementations or server-run code with the idea itself. Stored procedures are bad because your RDBMS has a crappy compiler? Hmm...

(One might argue, of course, that SQL in itself turned out to be a lousy interface protocol for relational data processing, and that it caused a lot of pain to begin with. But that's a different topic.)

[batou]

I'm actually arguing that my RDBMS is no place for a compiler. I want to compile everything externally, test it and then deploy it. Not deploy it, compile it, cross fingers.

[abrookewood]

Some counter-points I've heard made: 1) Performance. Stored procedures are fast, meaning it will be longer before you need to scale out. 2) Security. If you only use stored procs, you're a lot less exposed to SQL injections etc.

I don't really have a firm opinion either way, but it's not as clear cut as you are making out.

[batou]

Counter-counter-points:

1) Stored procedures aren't that much faster than issuing plain SQL over the connection. The main performance bottlenecks in a RDBMS are cache and IOPS. Regardless of where you execute those, they are all inside that black box after the query is parsed. You also get the added pain of cached query plans which fuck up performance when the query optimiser makes assumptions about table statistics and stores them with a stored procedure. (SQL Server and Oracle at least are guilty of this).

2) The only place I've had SQL injection attacks in the last few years is where people have used dynamic SQL inside stored procedures (sp_executesql) and not escaped them properly. Outside of that, both ORM and proper parameter binding make this entirely irrelevant.

It's completely clear cut IMHO.

[untog]

Performance. Stored procedures are fast, meaning it will be longer before you need to scale out.

That was once the case, but every major DB now caches execution plans for commonly run queries.

[FLUX-YOU]

>If you only use stored procs, you're a lot less exposed to SQL injections etc.

How does that help you vs. prepared statements in any typical language?

I've seen SQL statements in SPs that are concatenated (|| in oracle) to varchar fields from a table and I thought that would be just as vulnerable?

[adamors]

For one, stored procedures are hard to test, debug, maintain and check into source control.

But don't let that get in your way of ignorantly generalising about web developers.

[glogla]

Stored procedures may be all of those things, but they don't have to - it's just that most of the time, developers don't really care, so they have fancy versioning, deployment and continuous integration for all their code, except for stored procedures.

Here is interesting talk about database migrations and stored procedures and unit tests: http://www.pgcon.org/2013/schedule/events/615.en.html

Also, DB procedures are not easy to "debug" in the traditional way, but SQL client is basically the first REPL every programmer becomes familiar with. You can easily step stored procedure by running it's commands one by one, unless it's fancy Oracle forall loop with cursor or something (and the cursor select can still be selected as normal).

Also, databases tend to have more strong data types than programming languages in general so putting constraints in DB means, that bad data are not savable in the system.

[jeletonskelly]

> so they have fancy versioning, deployment and continuous integration for all their code, except for stored procedures.

Exactly, because those things are extremely important to how code gets shipped and delivers value to the business. Stored procedures become a huge risk to future development which ultimately means it's a risk to the businesses ability to deliver value. What happens when you need to change DB vendors because the business has been so successful that you've outgrown a relational database? You have to rewrite the ENTIRE MC portion of your MVC application. Why would someone ever do this?

[batou]

Hmm no.

Avoid state at all costs. Stored procedures are stateful. Schema and migrations is pain enough already.

Write me a check constraint that validates an email address being put in a varchar column and reports back a sensible message which can be bound to an entry field with metadata about the error.

Write me a constraint and key arrangement which is unique across two and three columns in separate groups.

No. You're wrong.

[nunwuo]

> Avoid state at all costs. Stored procedures are stateful. Schema and migrations is pain enough already.

What do you mean by that? How is having a bunch of queries in a stored procedure more "stateful" than having the same queries in the application?

> Write me a check constraint that validates an email address being put in a varchar column and reports back a sensible message which can be bound to an entry field with metadata about the error.

Postgres gives you metadata about the error, though the error message will still be a generic "CHECK constraint violated" or some such.

> Write me a constraint and key arrangement which is unique across two and three columns in separate groups.

I'm not sure what you want to see based on that description, but surely you're not advocating enforcing unique constraints in the application?

[batou]

Stateful:

If I have to load the stored procedure into the persistence engine then that step is required. This is no more stateful than queries in the application but it means that the relevant state in both the application and the database engine needs to be reloaded and constantly sychronised. Ergo, two times the work.

CHECK constraint violated is no good for humans. Prevention is better than cure here.

Why shouldn't I enforce unique constraints in the application?

1. Open a transaction

2. Get a user by name from the ORM.

3. Exists? Tell user that the username is already registered.

4. Doesn't exist? Save new User instance.

5. Commit transaction.

Steps 2 and 3 can be as arbitrarily complicated as you need them to be, are fully testable and cheap with anything that uses MVCC.

[brightball]

"Why shouldn't I enforce unique constraints in the application?"

You should to both. For all the reasons you mention, it's often cleaner to just do it in the application especially when you can use a framework with a simple "validate_uniqueness" flag.

But, what you're describing is also the very definition of a race condition. It's the same reason you don't increment counters by retrieving them, adding 1 to it and then saving the number back to the database and instead pass in an increment command.

Check it in the application but let the database make sure it doesn't get violated in a race condition. There's a significant amount of either/or in this entire conversation (not just you, the whole thread) when the database absolutely can and should be leveraged for certain things.

It's extremism and purism where the problems get introduced (in both directions).

[giaour]

> Why shouldn't I enforce unique constraints in the application?

This tightly couples your database to your application. You can no longer guarantee that your database is reliable when used otherwise.

[rapala]

Or you could do:

1. Insert new User instance 2. Unique constraint violation? Tell user that the username is already registered.

[lpsmith]

There is a good chance that your proposed algorithm to enforce a uniqueness constraint in the application won't work. As in, you've left out enough details that would be critical for getting it right, and in my experience, a lot of programmers would only get this right by accident if they get it right at all.

First problem is that the SQL standard provides no way to make this work portably on any standards-compliant database. So right there you are going to have to code to the database to one degree or another.

So, let's say you want to make this work in Postgres. Now, you'll need to be using Postgres 9.0 at least; otherwise your uniqueness constraint won't be a uniqueness constraint.

Try this, in any version of Postgres. Open up two psql sessions. In one, run a `create table unique (x text);`. Then run `begin isolation level repeatable read; select * from unique where x = 'foo';` in one of the sessions. Repeat those two commands in the other sessions.

Neither session sees 'foo'. So now both can go ahead and run `insert into unique values ('foo'); commit;`. Both transactions will succeed, and you can confirm that there are now two instances of 'foo' in the table.

In fact, `begin isolation level serializable` in PostgreSQL 9.0 or later is the minimum isolation level to make this work. And, you will need retry logic around the transaction in case of a serialization failure. (Perhaps your DB access layer or language would hide this latter detail from you, or perhaps not.)

In PostgreSQL 8.4 and before, serializable and repeatable read were equivalent, and both were still SQL standards compliant. In PostgreSQL 9.0, the repeatable read isolation level stayed the same, while the serializable isolation level was strengthened.

Unless you can accept a certain level of degraded accuracy by using a probabilistic construct such as a Bloom filter, by far the biggest cost of maintaining uniqueness is the index. And you'll need that index whether you use the database or the application to enforce uniqueness.

And, judiciously pushing computation onto a database can actually be cheaper for the database as well as its clients. This scenario is likely to be one of those situations.

[dragonwriter]

> CHECK constraint violated is no good for humans.

Well, sure, an application should respond to DB errors by presenting appropriate messages on the UI, just like any other errors it encounters. You should only see "CHECK constraint violated" if you are bypassing the app and using the DB. Otherwise, you should see something nice provided by the app.

> Why shouldn't I enforce unique constraints in the application?

Because you should do it in the database whether or not you do it in the application, and then once you have, well, DRY.

[herge]

Not enforcing as the final line, but reporting the error back to the user in a way that can be handled/translated/etc.

[dragonwriter]

> Avoid state at all costs. Stored procedures are stateful.

Stored procedures are no more state than application code is.

> Write me a constraint and key arrangement which is unique across two and three columns in separate groups.

What does "unique across two and three columns in separate groups" mean? I get that its something more complex than a simple multicolumn uniqueness constraint, but not what it is supposed to do.

I suspect that whatever it is can be done with PostgreSQL -- possibly using the (relatively) new exclusion constraints -- but I can't quite be sure without more clarity on what you mean.

[bni]

"hard to test, debug, maintain and check into source control."

Why? I have never had problem with any of these. SPs is just imperative code like any other imperative code.

[adamors]

Well, you cannot isolate the code, you cannot unit test it, you cannot use a debugger, cannot set breakpoint, have stack traces etc. You are tied to the database at all times.

In my experience, every stored procedure that is larger than 2-3 lines is a headache.

[bni]

All of those are no problem with the right tools. Any database IDE can debug SPs. You can unit test SPs like any other code just use a testrunner.

[glogla]

Yeah. I suspect that lot of hate of logic in DB is because of bad Oracle setups many years ago, kind of like lot of people think SQL is useless because MySQL is.

[arethuza]

I'm not a huge fan of stored procedures - but I'm pretty sure you can debug stored procedures in SQL Server pretty easily from Visual Studio - I think you can "step into" the call to SPs while debugging client code.

[jasonlotito]

I tell that to our DBAs who test, debug, maintain, and check into source control our SPs.

[ilitirit]

I find it strange when people adhere to these extremely dogmatic ideas about stored procedures. They appear to be either on one end of the scale or the other, ie. they either put all their logic in to Stored Procedures, or refuse to use them at all.

Of course, the reality is that people who use them reasonably do exist and are probably in the majority. You just rarely hear them talk about it because I suspect that they hold the same views about Stored Procedures, Constraints and any other DBMS feature as they do with any other software development tool ie. Use the right one for the job.

[glogla]

Yeah. Lot of the time, for a CRUD app, the who layer between rendering and data storage doesn't really do much besides validations, and those can be in database, so whole middle layer can be unnecessary.

Sometimes, the logic has to be in database, because it is single point of truth and because many application servers are hard to synchronize with regards to "you get max 3 attempts at login" or "you have to have enough balance to do bank transfer".

Sometimes, lot of your logic is in database, because database can do a lot of things in really fast and practical way, like aggregation and reporting and various data exploration tasks.

Sometimes, the database is just dumb store of object oriented data.

It depends on the application.

[kijin]

> Why people in the web world don't use stored procedures and constraints is a mystery to me.

You can blame MySQL 4.1 for that :(

Most people who call themselves "web developers" haven't even heard of PostgreSQL, or even if they've heard of it, have no use for it because their usual clients are stuck with MySQL-only web hosts who have only just managed to upgrade to PHP 5.3.

[ozzie80]

Most people, really?

[chx]

Yes. HN is a bubble. There are ~700 PHP questions on SO a day and ~150 node.js. This is just one pair of numbers, you can mine your own whatever you like but you'll realize there are massive amounts of "web developers" with a ... low amount knowledge.

[adamors]

Thinking most web developers are still shipping PHP 5.3 apps on shared hosts is also a very outdated view.

[greghinch]

Globally, it's not.

[kijin]

The latest version of WordPress is still compatible with PHP 5.2.4 and above, so anyone who builds a WordPress site is effectively shipping a PHP 5.2 app.

[spdionis]

They do recommend php 5.4 though, and afaik they do try to push the community to upgrading.

[_lce0]

While I do agree with you, I want to make a distinction between shipping and building an application.

IMHO the term "developer" should not be applied to those that can just ship but rather those who can also build.

It doesn't matter if they are web, desktop, nor low-systems developer actually

Most auto-called web developers are just "web masters"

[kijin]

Now you're just redefining "developer".

No True Scotsman puts sugar on his porridge, and No True Developer just installs WordPress.

On the other hand, even Rails and Django encourage you to use the ORM whenever possible, so even a "developer" who builds apps on a modern framework is unlikely to be familiar with advanced SQL features.

[mark_sz]

I'm guessing you are not developer, because that kind of comment wouldn't come from someone who's thinking logically.

We don't need another flame war here.

And yes, most of the web is build on Wordpress/PHP - but you don't need to be a developer to install Wordpress.

[kijin]

What does logic have to do with it?

I'm just stating what I believe to be a fact: that the majority of web developers in this world never think of PostgreSQL as an option. I don't care whether that's a logical thing for them to think. It's just a fact, whether I like it or not.

If you think I'm wrong about the facts, please feel free to open a phone book in any part of the world other than the Bay Area, call up a decent sample of people who self-identify as web developers, and find out what percentage of them have ever heard of, let alone used, PostgreSQL.

[GrinningFool]

So you start off ok here:

    I'm just stating what I believe to be a fact... 

But then you move on to say:

    It's just a fact, whether I like it or not.

So which is it? Do you believe it to be a fact, or is it a fact? And if it is, where's your evidence?

(I happen to agree with your opinion, but the semantics here bug me.)

[kijin]

Sorry for the loose use of language. Everything that follows the colon after "I believe to be a fact", until the end of that paragraph, is the content of what I believe, including the statememt "It's just a fact." I believe that it's a fact.

Anecdotal evidence: I've interacted with dozens of other people who call themselves web developers over the years, and most of them (outside of Silicon Valley) have never used PostgreSQL, nor any advanced features of SQL in any other RDBMS.

Objective evidence: the large market share of WordPress, Drupal, and other content management systems that don't use any advanced database features; as well as the large market share of frameworks such as Rails, Django, and Laravel that encourage developers to stick with the ORM and not care about advanced database features.

[GrinningFool]

Thanks for clarifying. It does seem all too common to pretend the database is a black box (via ORM) in the most popular frameworks.

[framp]

I don't think using stored procedures should be the focus of the project.

PostgREST is great because it lets you kickstart a CRUD application with ease.

I'm mainly a node.js developer nowadays and I'm using some frameworks to kickstart APIs for my clients - and then I jump in and add features.

What I really want is a solution to build a API server which deals with authentication, exposing my models through REST and other boring and repetitive stuff. In this way I don't have to focus on everything, but just on the specific problem I'm solving.

I don't think there is a valid solution out there right now.

That's why I'm contributing to PostgREST and I hope to see even more features coming out of it (eg: better authentication, maybe with 3rd party logins).

[kaikokaur]

You may want to see http://www.zazler.com/ or https://www.npmjs.com/package/zazler

[framp]

I'm using hapi + sequelize or loopback actually. Zazler looks interesting, thanks for the link!

[psaintla]

Around 2005 I worked for a fairly large company that did exactly what you're suggesting with Postgresql and it was a complete disaster. Have you ever tried implementing sharding with all of your business logic in stored procedures? Have you ever tried hiring people who understand pl/sql and WANT to work with it? I have done both and it is a nightmare, once you get to the point of having to shard data you end up in one of two places:

1.) The sprocs become insanely complex because they have to be shard aware.

2.) You slowly start moving more of your code that was in sprocs to your application so now you've got two problems.

As for hiring, put out an ad for an engineer with pl/sql knowledge better yet put out an ad for someone who wants to learn and use pl/sql. Good luck finding enough of those people to get any significant work done.

[fweespeech]

> This is good work and if I ever did web development, it would be like this. Why people in the web world don't use stored procedures and constraints is a mystery to me. That this approach is seen as novel is in itself fascinating.

Regardless of the other points people brought up...

Sharding a database with stored procedures and constraints as you advise is a nightmare because you now have a completely separate deployment process [deploying stored procedures, if you think this doesn't require a deployment process across a sharded infrastructure...I have no words].

Using an internal web framework is much, much easier than maintaining two separate deployment processes. Especially when one of those processes has to take down nodes to avoid some shards having different stored procedures than other shards.

[devnonymous]

...and it's not just databases. OS capabilities (eg: vm tuning, bumping up the default sysctl limits, etc) are ignored and the problems arising of such disregard are then dealt with by adding layers to the application like distributed caches and other ^scaling^ solutions.

[ecopoesis]

Because databases are a very poor fit for APIs? This is one of my biggest problems with high holy REST: it generally just means reimplementing your SQL API in HTTP semantics.

APIs should be about encapsulating business logic. Databases should be about storing data in a reliable, predictable way.

[benkant]

That's what views are for.

[jasonlotito]

> Why people in the web world don't use stored procedures and constraints is a mystery to me.

We do. At least some of us, and honestly, it's not something I think about as being exceptional. I don't always use them, but I much prefer having a nice API of SPs to use rather than having to have custom SQL all over the place. DRY applies to writing queries just as much.