[smacker]

I like using postgres for everything, it lets me simplify infrastructure. But using it as a cache is a bit concerning in terms of reliability, in my opinion.

I have witnessed many incidents when DB was considerably degrading. However, thanks to the cache in redis/memcache, a large part of the requests could still be processed with minimal increase in latency. If I were serving cache from the same DB instance, I guess, it would cause cache degradation too when there are any problems with the DB.

[aiisthefiture]

Select by id is fast. If you’re using it as a cache and not doing select by id then it’s not a cache.

[smacker]

absolutely. But when PG is running out of open connections or has already consumed all available CPU even the simplest query will struggle.

[motorest]

> But using it as a cache is a bit concerning in terms of reliability, in my opinion.

This was the very first time I heard anyone even suggest that storing data in Postgres was a concern in terms of reliability, and I doubt you are the only person in the whole world who has access to critical insight onto the matter.

Is it possible that your prior beliefs are unsound and unsubstantiated?

> I have witnessed many incidents when DB was considerably degrading.

This vague anecdote is meaningless. Do you actually have any concrete scenario in mind? Because anyone can make any system "considerably degrading", even Redis, if they make enough mistakes.

[baobun]

No need to be so combative. Take a chill pill, zoom out and look at the reliability of the entire system and its services rather than the db in isolation. If postgres has issues, it can affect the reliability of the service further if it's also running the cache.

Besides, having the cache on separate hardware can reduce the impact on the db on spikes, which can also factor into reliability.

Having more headroom for memory and CPU can mean that you never reach the load where ot turns to service degradation on the same hw.

Obviously a purpose-built tool can perform better for a specific use-case than the swiss army knife. Which is not to diss on the latter.

[didntcheck]

> This was the very first time I heard anyone even suggest that storing data in Postgres was a concern in terms of reliability

You seem to be reading "reliability" as "durability", when I believe the parent post meant "availability" in this context

> Do you actually have any concrete scenario in mind? Because anyone can make any system "considerably degrading", even Redis

And even Postgres. It can also happen due to seemingly random events like unusual load or network issues. What do you find outlandish about the scenario of a database server being unavailable/degraded and the cache service not being?

[abtinf]

Inferring one meaning for “reliability” when the original post is obviously using a different meaning suggests LLM use.

This is a class of error a human is extremely unlikely to make.