feat: avoid double fetches on `ibis.duckdb.connect().read_csv("https://slow_url").cache()`

[NickCrews]

Is your feature request related to a problem?

When you call .read_csv() on the duckdb backend, this makes duckdb actually go fetch [some] of the data in order to sniff the schema. Then, when you call .cache() on the created view, it actually goes and fetches the full data.

This is related to #9931.

What is the motivation behind your request?

I am working on relatively large tables on a slow internet connection. Each fetch takes about 30 seconds. I would like to avoid this double fetch.

Describe the solution you'd like

Since the result of .read_csv() needs to be a Table with a known schema, it is going to be required to fetch some data during that function call. So, I think we need to add an optional argument to the function, or create entirely new function. I would vote for adding params if we can come up with something sane. Maybe cache: bool?

What version of ibis are you running?

main

What backend(s) are you using, if any?

duckdb

Code of Conduct

• I agree to follow this project's Code of Conduct

[cpcloud]

Can you break down the timing of:

CREATE VIEW v AS FROM read_csv('slow_url')

and

CREATE TABLE t AS FROM read_csv('slow_url')

?

It's not clear that there's a "double fetch" (as in they two fetches are equivalently slow) so much as a small fetch followed by a large fetch.

[NickCrews]

Yeah good idea, I'll do that and report back.