Expiring keys in Postgres with a created_at column and a pg_cron job is very easy (at least, if you're comfortable in Postgres). Redis is world class though of course, and can be deployed turn-key in basically any environment. If you're more comfortable in Redis than Postgres, more power to you. Different choices can be pragmatic to different people.

Personally for a greenfield project, my thinking would be that I am paying for Postgres already. So I would want to avoid paying for Redis too. My Postgres database is likely to be underutilized until (and unless) I get any real scale. So adding caching to it is free in terms of dollars.

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frollogaston 11 hours ago | parent [-]

I'm comfy with Postgres though, like I'll center my entire backend around it and do the heavy lifting in SQL (never ORM). It's more that I don't want to depend on a cronjob for something as fundamental as a cache.

Usually Postgres costs a lot more than Redis if you're paying for a platform. Like a decent Redis or memcached in Heroku is free. And I don't want to waste precious Postgres connections or risk bogging down the whole DB if there's lots of cache usage, which actually happened last time I tried skipping Redis.

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maxbond 10 hours ago | parent | next [-]

I can understand being nervous about some cron job running on some other service, but what's concerning about a cron job managed inside of Postgres with pg_cron? If that doesn't run, your database is probably down anyway.

Postgres might cost more but I'm probably already paying. I agree that exhausting connections and writing at a high rate are easy ways to bring down Postgres, but I'm personally not going to worry about exhausting connections to Postgres until I have at least a thousand of them. Everything has to be considered within the actual problem you are solving, there are definitely situations to start out with a cache.

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frollogaston 10 hours ago | parent [-]

I might be ok with this if it were built in, but pg_cron is an extension, so first off you might not even have access to it. And then you still have to monitor it.

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maxbond 10 hours ago | parent [-]

Seems like it's available on all the major providers.

	▲	frollogaston 10 hours ago \| parent [-]
		Heroku doesn't have it. That's actually kinda annoying that they don't, cause the others do. AND they no longer have free Redis, so that changes things a bit. Edit: well a tiny bit, max $3/mo

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motorest 10 hours ago | parent | prev [-]

> Usually Postgres costs a lot more than Redis if you're paying for a platform.

You need to back up your unbelievable assertion with facts. Memory cache is typically far more expensive than a simple database, specially as provisioning the same memory capacity as RAM is orders of magnitude more expensive than storing the equivalent data in a database.

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frollogaston 10 hours ago | parent | next [-]

I didn't say it's cheaper for the same cache size. But yeah a base tier Redis that will carry a small project tends to be a lot cheaper than the base tier Postgres.

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motorest 10 hours ago | parent [-]

> I didn't say it's cheaper for the same cache size.

So be specific. What exactly did you wanted to say?

> But yeah a base tier Redis that will carry a small project tends to be a lot cheaper than the base tier Postgres.

This is patently false. I mean,some cloud providers offer nosql databases with sub-20ms performance as part of their free tier.

Just go ahead and provide any evidence, any at all,that support the idea that Redis is cheaper than Postgres. Any concrete data will do.

	▲	frollogaston 8 hours ago \| parent [-]
		Look at the Heroku pricing. If you don't like Heroku then look at AWS pricing. Specifically for Postgres, not a NoSQL DB (which Redis can be too)

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MangoToupe 10 hours ago | parent | prev [-]

Why would you cache the entire database though? Seems like an apples to oranges comparison.

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motorest 10 hours ago | parent [-]

> Why would you cache the entire database though?

I have no ideas where did you got that from.

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MangoToupe 10 hours ago | parent [-]

> specially as provisioning the same memory capacity as RAM is orders of magnitude more expensive than storing the equivalent data in a database.

I'm not sure how else to interpret this

	▲	motorest 9 hours ago \| parent [-]
		Why are you confusing memory capacity as a requirement to store the whole database in memory? I mean, think. What do you think is the biggest performance bottleneck with caches, and how does this relate to memory capacity?