if you rely on triggers for data integrity, then I guess this is one more case where MySQL is letting you down and allowing your data to get corrupted unless you're really careful.
While it's not always good design to use triggers for this, sometimes, it's a valid reason to use them for integrity checking or enforcing. Having `on delete` triggers not run for some delete's is violating the principle of least surprise.
When feature break this way, people start to distrust them and best practices get adopted that discourage using them, killing the features all together.
Using a database that does not have this misfeature, both triggers and foreign keys are perfectly safe to use, but because the one database that is the most widely used has issues like the one described here, you often hear the recommendation to not use triggers or even foreign keys.
Yes, you can potentially move the logic normally contained in either of them into the application, but as you deal with more concurrency and as you start accumulating bugs, sooner or later your data will be messy and you will need to add cleanup-scripts, or, heaven forbid, work around messy data in your application logic (don't. do. that. it's the path to the dark side of unmaintainability).
Or, of course, use a database system whose features work correctly and the principle of least surprise is in effect.
mysql is good for very high transaction rate platforms, that mostly rely on simple features. for this, it generally outperforms most of its competition in the traditional RDBMS space, and why companies like twitter and facebook use it. mysql likes simple, well designed queries.
postgres usually outperforms mysql for more complex operations, but is not as fast as mysql for simple ones.
sqlite is really only appropriate for things like mobile or desktop applications or things with generally low concurrency requirements.
i would be careful throwing the baby out with the bath water in your dismissal of mysql, but thats just my opinion:)
can you shed some more detail on that apple uses triggers with sqlite? that is interesting to me, and would like to learn more.
For apple: jailbreak
go to home dir
apt-get install sqllitex.y
apt-get install bash find
list all the files / dir find the contacts
read the man of sqllite and have it tell gracefully the content of the table
Something like this:
http://beauty-of-imagination.blogspot.ca/2014/03/backuping-m...
Well it is true mysql is fast ... when it is not a problem.
They sacrificed correctness (stuff about big O notation in worst case) for benchmarks... and it works ... amazingly well as long as you are not under heavy load or give up on integrity, or relationship, or correctness.
Amazing. As long as you store data that need not to be transactional, or relational, or needing integrity mysql is fast. When data matters, or load is heavy mysql is just not there. It is chaotic, inconsistent, unicode retarded... full of pits... and resource greedy.
Sure, if you are a masochist, or if you fear to loose your job and need to elevate pain to the rank of art, then mysql is alright.
I have been sysadmin as long as developer and on both sides of the track mysql is insanely not consistent. (sysadmin: 400 config parameters, replication that fear any butterfly flapping its wings near a network cable, dev: collation behaviour, (clumsy) LDAP integration for auth, inconsistencies...).
I even prefer MSsql to mysql. I have been working almost only in linux environment since 2000, and I still think MySQL is crap. 10 years of horror stories with mysql made me hate it as much as taking LSD before trying to fill your taxes.
sqlite is really only appropriate for things like mobile or desktop applications or things with generally low concurrency requirements.
I think what you mean here is low concurrent write requirements.
(Edit in response to below: Isn't sqlite file oriented and read-only opens eschew locking? Thus replication via network filesystems should be adequate, no?)
Yes, agreed, if we are talking about straight concurrency only.
Other things like replication, are also not there, so it's not what I would choose for a website database, but if you can serve all your reads from one server, and don't care about high availability, then go for it.
> Yes, you can potentially move the logic normally contained in either of them into the application, but as you deal with more concurrency and as you start accumulating bugs, sooner or later your data will be messy and you will need to add cleanup-scripts
I agree with most of what you said, but in many many use cases data integrity can be maintained in application code (a statically typed system helps), it simply can't be true that all those applications running on NoSql database will have messy data and/or cleanup-scripts.
furthermore, foreign keys are not performant at mass scale on both pg or mysql or any traditional RDBMS. if your trying to do several thousand ops per second, the vector of index contention greatly goes up if there is FKs littered all over your schema.
nosql or sql large platforms almost always have some amount of work always ongoing to clean, shuttle, and maintain data integrity.
that doesn't make me not a fan of them; for lower transaction rate applications ( which most probably are ), they are a small time investment to have some sanity checking. but it's a right tool for the job thing.
this is yet another reason why people dislike FKs in best practice stuff.
Edit: Hi down-voters. Curious to hear why I'm being down voted and possibly be offer a rebuttal?
Foreign keys are not convenience artifacts. They are essential for enforcing data correctness. One doesn't simply opt out of their usage simply because one is "not a fan" of foreign keys.
I've experienced several highly-performant, correct databases with concurrent clients from around the globe ... and they had no enforcement of foreign keys.
Yes, foreign keys were essential to data correctness. No, they were not being enforced in production. Stew on that just a bit. Not enforced in production.
During client application development, development databases enforced the constraint. Any errors resulting in foreign key mismatches disqualified the client app for release. The applications were required to be aware of the constraint and to learn to work within it. Production gained the speed benefits of not having to enforce the foreign keys.
You can indeed eat your cake and have it, too, iff you are disciplined.
This might be the case if you have one and only one application interacting with the database, and your unit tests include each and every permutation/edge case.
It is very common to have many applications, from different vendors and from different time periods interacting with a database.
It often also happens that data can be modified directly in the database, not via the application. I agree this is not best practice but in larger enterprises it happens.
Once you start implementing foreign keys in the client you are adding a lot of complexity to a problem that most mature relational database system do well enough to be trusted by a lot of traditional financial institutions.
What if it is the difference between your schema working under high transaction rates or not? Or, the difference between buying much more database hardware and having smaller shards to avoid index contention. (which, is $$)
FKs are rarely present in extremely high transactions per second systems that operate on the same few tables. This is due to index contention and locking.
I say this with lots of experience working on different production systems that see hundreds of thousands of transactions per second. I have yet to see one arrive at these kind of numbers using foreign keys, unless it's something like a giant shared hosting platform, that is operating on hundreds and hundreds of different tables. (therefore, less index contention)
Often, in these shops, data correctness is not validated in realtime in this way, but often in a way that is not in the critical path of answering queries. (more like, eventually consistent). Some places have entire teams for this.
To your point on correctness, my experience ranges a lot in areas where correctness can be eventually consistent. For something like healthcare or banking, you would rather spend the money on way more hardware, because you can't afford correctness to be off. However, with things like globally scaled social apps, this is just not the case.
Most people tend to still use Oracle in those situations. Which is legions slower , and legions more expensive than mysql or pgsql.
I am afraid your premise is incorrect. Foreign keys can be enforced (particularly on insert-only or insert-mostly workloads) with very little contention, even in a distributed system: http://www.bailis.org/papers/ramp-sigmod2014.pdf
And lest you think there is some hidden constant factor here that destroys real performance at the cost of "scalability," the techniques from that paper were used to completely destroy the TPC-C benchmark: http://arxiv.org/pdf/1402.2237.pdf
Admittedly this stuff is not yet implemented in traditional RDBMSes, but there is absolutely no reason why it could not be and I fully expect it to in the future. Certainly, if you are having performance problems now, this knowledge doesn't help. But I'd venture to guess (from personal experience) that most people removing foreign keys are doing it preemptively, rather than evaluating whether it is actually causing performance problems.
That's all the active bugs against MySQL. Note that this 10 year old bug isn't the oldest.
This is the oldest, from March 2003: https://bugs.mysql.com/bug.php?id=199
Note someone submitted a fix for that over a year ago (and verified under the OCA in November) but it still hasn't shipped. This is a bug that should never have taken 11 years to fix.
MySQL, for all its strengths, often feels like there is a bunch of typical geeks running the show. Lots of focus on the 'sexy' new features, not so much focus on keeping the lights on.
It's probably not, but I'd rather not have the feature at all than think that it's there and working but actually not doing what I've asked it to. The current short-term fix would be to make it raise an error when you try to create such a trigger, so at least no one would be using it for now.
Somehow those seem less important. Maybe it's because I cut my teeth on Sybase and Oracle rather than noSQL, but if triggers don't work, I would really hesitate to call that a RDBMS.
The question is if one should "fix" this at all. If you change the behavior from "foreign keys do not activate triggers" to "foreign keys activate triggers", everyone who uses triggers will have to audit their applications for potential problems. And for large applications, that can be a lot of work.
MariaDB documents "foreign keys do not activate triggers" as the standard behavior:
Personally, I am grateful for software that changes as seldom as possible. I don't want to spend time on "updating" my application because something down in the stack changed.
Mysql has its uses. Keeping a list of people you don't know on a social network is a great use case. Recording cat video URLS is another. Keeping track of money is not a good use case for mysql. Simple as that.
My favourite is this one is the correlated subquery bad query plan selection: http://bugs.mysql.com/bug.php?id=9090 "It's not a bug, it's a feature". You can always find a way to work around this stuff, or you can use postgres or another db that considers thi stuff important.
triggers...bah. how about CHECK constraints? (http://stackoverflow.com/a/2115641/34549) The irony is that the workaround for CHECK constraints being silently ignored is to use a trigger.
Probably because they don't want to break their compatibility with mySQL, a decision of theirs I highly appreciate. Being able to drop Maria in for mySQL without having to rework a lot of things has been a huge time saver.
I don't understand some of the people commenting on the bug report. If they really want it fixed, then they should fix it. Making rude comments isn't going to make it go any faster.
As someone who had issues with a 4+ year old bug in FileZilla, can confirm. First time I developed anything serious in C++ and it took me only two evenings to develop a patch. Then some back and forth on the bugtracker, but it made it in soon after.
(For those interested, it's the ability to create a new, empty file on the server.)
I don't know how the trigger system is structured under the hood, but I could imagine it being somewhat comparative if you can properly call them. At least one of the commenters could have tried something or asked for pointers where to find it, that triggers others to actually work on it or at least help them work on it.
While it's not always good design to use triggers for this, sometimes, it's a valid reason to use them for integrity checking or enforcing. Having `on delete` triggers not run for some delete's is violating the principle of least surprise.
When feature break this way, people start to distrust them and best practices get adopted that discourage using them, killing the features all together.
Using a database that does not have this misfeature, both triggers and foreign keys are perfectly safe to use, but because the one database that is the most widely used has issues like the one described here, you often hear the recommendation to not use triggers or even foreign keys.
Yes, you can potentially move the logic normally contained in either of them into the application, but as you deal with more concurrency and as you start accumulating bugs, sooner or later your data will be messy and you will need to add cleanup-scripts, or, heaven forbid, work around messy data in your application logic (don't. do. that. it's the path to the dark side of unmaintainability).
Or, of course, use a database system whose features work correctly and the principle of least surprise is in effect.
PostgreSQL is one of these, by the way.