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Comment by sandstrom | Hacker News Reader

Well, we're kind of comparing MongoDB of ~2011 (when The Guardian started using them) with Postgres of today.

One major change is that in 2010 you couldn't always run your whole DB in RAM, so there were some real performance benefits with MongoDB.

Another difference is that MongoDB was early with great JSON-support. Something that Postgres has since gained.

I think there are pros and cons with both. If I'd chose one today, for most tasks I'd probably chose Postgres.

That said, to understand why people made those choices, you need to 'teleport back' to that time and compare them in that year (given the tradeoffs at that time).

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If somebody is teleporting back then, the fact Mongo had a _global_ Mongo instance level lock for writes should be more than enough for people to run screaming.

I worked with databases that only had table level locks(not row level) and there were more than enough occasions I cursed the creators.

Instance level(& indeed DB level) is insanity unless your DB is a read only DB.

Not saying you're wrong, but a news site and CMS has different database requirements than many other products.

They have very few write actions; in the Guardian's case hundreds of authors publishing a few articles a day, versus millions of users reading data. Writes would be sporadic and batched.

News products also changes more rapidly than you might expect. A modern news team may be writing and shipping code to better cover a breaking news event. I can imagine why a document store would be appealing to them.

I don't think Mongo was used much by people who would know why instance level lock is bad, or even what it is. And if someone who knew came later, it was too late - Mongo's proprietary querying language is a vendor lock-in.

Oh! From The Guardian write up I had the impression they were using it until mid 2018..

It is not easy to switch, so until the pain is too big, one doesn't do it.

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