Now that I have taken a closer look, the code looks significantly better than it seemed at first glance, though there are still peculiarities, and some drawbacks.
An unfortunate aspect is that the code has become a bit more bloated in some regards due to usage of Result, instead of an implicit elog() macro and similar. Passing Result around, in some ways as an alternative to an unwinding exception, is cleaner in some ways, but it also bloats the code somewhat.
The rewrite also could have simpler code in some cases, like
https://github.com/malisper/pgrust/blob/3646a73515a5e4ac7d0b...
could perhaps just be
match syscache_seams::search_pg_class_full_form::call(ctx.mcx(), relationId)? {
Some(form) => Ok(form.relhassubclass),
None => {
Err(ereport(ERROR)
.errmsg(format!("cache lookup failed for relation {relationId}"))
.into_error())
}
}
I see a lot of MemoryContext. I am not sure how much that bloats the code (though the C code is bloated due to C's issues and problems, like re-using collections and such). Does it incur an overhead?
> The rewrite also could have simpler code in some cases
The Rust code is a literal translation of the Postgres code which returns the value at the end instead of an early return.
> I see a lot of MemoryContext
MemoryContext in C is used for multiple reasons: 1) performance 2) keeping track of how much memory has been allocated and where and 3) preventing memory leaks.
Reasons 1 and 2 are still relevant for Rust. The challenge is in C memory contexts are stored in a global variable. Global variables don't work well with the rust borrow checker so I opted for passing memory contexts as function arguments instead.