Is is possible that PostgreSQL will replace these building blocks in the future?
- redis (Caching)
PostgreSQL has its own caching. It might not be quite as effective as redis', but you can us it if you are willing to take those trade offs.
What kind of caching does PG offer?
It has shared_buffers to cache the data it needs frequently (not query results, but the data needed to produce the results), and also uses the file systems cache. This is what I am referring to. I wouldn't recommend using PostgreSQL simply as a cache for something else, if you don't want any other features of the database. But if you want to throw Redis up as a layer of cache in front of PostgreSQL, maybe you should first see if that RAM, and a bit of tuning, can be used to make PostgreSQL fast enough to not need the Redis cache.
- s3 (Blob storage)
No. You can certainly use PostgreSQL to store blobs. But then, you need to store the PostgreSQL data **someplace**. If you don't store it in S3, you have to store it somewhere else.
I don't understand what you mean here. AFAIK storing blobs in PG is not recommended since it is not very efficient.
If the metadata is stored in PG and the blobs themselves are stored individually S3, you have a transaction atomicity problem. Solving that is not likely to be very efficient, either. You have to pick your poison.
