As the test test_streams_closed_read confirmed, when a stream shard is
closed, GetRecords should not return a NextShardIterator at all.
Before this patch we wrongly returned an empty string for it.
Before this patch, several Alternator Stream tests (in test_streams.py)
failed when running against a multi-node Scylla cluster. The reason is as
follows: As a multi-node cluster boots and more and more nodes enter the
cluster, the cluster changes its mind about the token ownership, and
therefore the list of stream shards changes. By the time we have the full
cluster, a bunch of shards were created and closed without any data yet.
All the tests will see these closed shards, and need to understand them.
The fetch_more() utility function correctly assumed that a closed shard
does not return a NextShardIterator, and got confused by the empty string
we used to return.
Now that closed shards can return responses without NextShardIterator,
we also needed to fix in this patch a couple of tests which wrongly assumed
this can't happen. These tests did not fail on DynamoDB because unlike in
Scylla, DynamoDB does not have any closed shards in normal tests which
do not specifically cause them (only test_streams_closed_read).
We also need to fix test_streams_closed_read to get rid of an unnecessary
assumption: It currently assumes that when we read the very last item in
a closed shard is read, the end-of-shard is immediately signaled (i.e.,
NextShardIterator is not returned). Although DynamoDB does in fact do this,
it is also perfectly legal for Alternator's implementation to return the
last item with a new NextShardIterator - and only when the client reads
from that iterator, we finally return the signal the end of the shard.
Fixes#7237.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200922082529.511199-1-nyh@scylladb.com>
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