> in any case.
In some cases. Are looking up a single indexed row in a small K-V table? Yep, slow. Are you generating reports on the last 6 years of sales, grouped by division within larger companies? That might be pretty fast.
I'm not sure why you'd even generalize that so overly broadly.
That's all true, so long as you completely ignore doing any processing on the data, like evaluating the rows and selectively appending some of them into a data structure, then sorting and serializing the results, let alone optimizing the query plan for the state of the system at that moment and deciding whether it makes more sense to hit the indexes or just slurp in the whole table given that N other queries are also executing right now, or mapping a series of IO queries to their exact address in the underlying disks, and performing the parity checks as you read the data off the RAID and combine it into a single, coherent stream of not-block-aligned tuples.
There's a metric boatload of abstractions between sending a UTF-8 query string over the packet-switched network and receiving back a list of results. 300ms suddenly starts looking like a smaller window than it originally appears.
There is nothing for us to take away in this discussion. So let me be the first to tune down: all I want to say is: don't take that 300ms as given, it sits in this uncomfortable region too short to be an async op and too long to be noticeable (anything between 50ms and 2s fits this bill). Most likely the query is doing something suspicious and would benefit the most to take a closer look at.
I was totally with you until that last sentence, then you lost me again.
Saying a DB query is too long by giving an arbitrary number is like saying a rope is too long. That’s solely dependent on what you’re doing with it. It’s literally impossible to say that X is too long unless you know what it’s used for.
To put in perspective, 300ms is about looping over 30GiB data from RAM, loading 800MiB data from SSD, or doing 1TFLOPS on a single core computer.
300ms to generate a report would be able to go through ~100M rows at least (on a single core).
And the implicit assumption that comment I made earlier, of course is not about the 100M rows scan. If there is a confusion, I am sorry.