Alternator Streams' "GetRecords" operation has a "Limit" parameter on
how many records to return. The DynamoDB documentations says that the
upper limit on this Limit parameter is 1000 - but Alternator didn't
enforce this. In this patch we begin enforcing this highest Limit, and
also add a test for verifying this enforcement. As usual, the new test
passes on DynamoDB, and after this patch - also on Alternator.
The reason why it's useful to have *some* upper limit on Limit is that
the existing executor::get_records() implementation does not really have
preemption points in all the necessary places. In particular, we have a
loop on all returned records without preemption points. We also store
the returned records in a RapidJson vector, which requires a contiguous
allocation.
Even before this patch, GetRecords had a hard limit of 1 MB of results.
But still, in some cases 1 MB of results may be a lot of results, and we
can see stalls in the aforementioned places being O(number of results).
Fixes#23534
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#23547
(cherry picked from commit 84fd52315f)
Closesscylladb/scylladb#23643
c6825920a6