In fact, we have a number of things assuming that values passed to Import
always fit within a single known shard, so, drop all the extra complexity
around this, drop the computation of fancy view/shard keys, and so on.
There's a lot of room left to improve this probably but it's at least
better, I think.
Unfortunately, there's a handful of things, basically all of which are
test cases, which were relying on this, so, we also add functionality
for splitting import requests by shards. But this allows us to stop
duplicating each shard's inputs one at a time... which turns out to
mean that we now care that the import operation can write back to the
import request. This only affects test cases, so we adopt a crufty
hack involving cloning import requests in those rare cases, and also
when reusing the same column IDs to write to the existence field that
we'd be using later to write to another field.
Note that even if we weren't overwriting the column IDs with positions,
we'd be sorting the column/row ID lists by row-then-column, which means
we'd still be corrupting the column ID lists. This may want to change
at some point.
We also reuse a single Tx for all the views, because DB-per-shard
means that should work fine, and reduces the cost of doing these
updates, probably.
We're reading timestamps as []int64, instead of allocating a time.Time
for each timestamp, just use the same logic to determine whether to use the
int64 timestamp that we would have used to decide whether to allocate it.
We still have to check the whole run, though, because we're providing a large
list of 0s instead of "no timestamps", for Reasons.
A nil Qcx is a crime against existence and makes baby pandas cry.
Having taken out the hack that tried to accommodate this when tests did it,
we now have to fix the tests. Oh no.
