all the other reasons beside - because at some point I might want to move the data cache off of the single machine and then I can do that with a couple of minutes work, yes then I am back to do I need redis why not use postgres, but I got months of better performance out of redis than I would have with postgres, if I need to move to separate machine I am probably doing good enough I can afford it.
Redis helps you get to the point (need cache on separate machines) where you might want to consider moving to postgres, or not because you don't feel it warrants the investment of programmer hours at that point.
on edit: got downvoted for ..? I guess what I said was so supremely stupid I deserved it. I do admit it was perhaps slightly obvious, but not so obvious that it warranted downvoting
the comment was quite clear that you are building today what you need today, and when you need to have another solution tomorrow you don't need to rebuild everything but just move it and update some connections - but if you build the other solution - keeping cache in the application - when you need the other solution you will need to rebuild everything.
How could that very clear statement be misunderstood as to be well I am building a bunch of stuff I might need to tomorrow, it is the exact opposite of that!
I guess it's my fault, nobody on HN seems to understand a single thing I say even though the words seem reasonably clear to me.
Redis helps you get to the point (need cache on separate machines) where you might want to consider moving to postgres, or not because you don't feel it warrants the investment of programmer hours at that point.
on edit: got downvoted for ..? I guess what I said was so supremely stupid I deserved it. I do admit it was perhaps slightly obvious, but not so obvious that it warranted downvoting