Rob Pike's Rules of Programming (1989)

Re:Rob Pike's Rules of Programming (1989) by nojvek on Wednesday August 12, 2020 @11:15PM (#24139619)

I don’t think people realize that databases themselves have a caching layer internally. Redis isn’t magical, you still have to send network packets to the other server.

Even when reading from disk via mmap, hot pages are in memory.

Sometimes postgresql is faster than redis because all it needs to do is read something from memory and spit it out in the right format.

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Re:Rob Pike's Rules of Programming (1989) by yashap on Wednesday August 12, 2020 @11:49PM (#24139781)

Totally. If the hot pages of your indexes and hot pages of your records mostly fit in memory, DBs mostly read from memory anyways. If they don’t mostly fit in memory, things can slow down a bit, but you’re likely better off vertically scaling your DB (more RAM) than adding a cache.

Looking up a normal sized record by id, with good networking in your data centre, takes ~1-2 ms round trip whether you’re reading from Redis/Memcached or MySQL/Postgres, and either can handle massive read load if sized properly. The cache just ~doubles your costs, is one more thing to patch/maintain, and introduces new sorts of bugs/outages.

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