Believe it or not, sometimes mongodb is the perfect tool for the job. It actually does support safe wrriting features, so some of the hype in that video is false. MySQL is always a great piece of the stack but it's not always good.
The video also shows its age, MongoDB hasn't stood still in the meantime. I put up a transcript of this movie because I found the mingling of the technical discussion with contemplating working on a horrible farm an interesting concept.
In all of our surveys (of web companies) the majority of people use MySQL. That certainly doesn't mean that its the best choice but using the most common software does come with a lot of obvious benefits.
It has a lot of weaknesses compared to postgres but it also has some definite advantages:
Clustered and covering indexes. If the data needed by a query is in an index there is no need to retrieve it from the table itself. This leads to better memory usage and cache locality.
MySQL has non transactional tables which use a lot less memory. If you store a large number of small records (say three ints or something) that table will use about a third of the memory a similar postgres (or Oracle) table would.
- Has more tested/reliable replication than anything else, possibly including Oracle (haven't tried the wacky 3rd party replication things like Goldengate or whatever, and don't believe in spending 6 figures on software licenses in general).
- Supports SELECT, INSERT and UPDATE
Why would I get anything else for a database? For more complicated stuff I have another approach that I employ called "programming".
We're a bit off-topic, but... Transactions on DDL, a lack of tons of gotchas, good replication, partial indexes, document orientation and querying, a pretty query language, ripping speed, horizontal scalability, a history of good architecture, consistent hashing, etc are reasons to select something other than MySQL.
