d8a9fdddbd
In the test we perform 2 consecutive writes where the first write
is supposed to increase the view update backlog above the mv
admission control threshold and the second one is expected to be
rejected because of that.
On each node/shard we have 2 types of view update backlogs:
1. for deciding whether we should admit writes
2. for propagating the backlog information to other nodes/shards.
For the second write to be rejected, it must be performed on a node
and shard which updated its backlog of type 1.
The view update backlog of type 2. is immediately increased on the
base table replica. For this backlog to be registered as a backlog
of type 1., it needs to be either carried by gossip (happening once
every second) or by attaching it to a replica write response. We
don't want to increase the runtime of tests unnecessarily, so we don't
wait and we rely on the second mechanism. The response to the first
base table write (the one causing increase in the backlog) carries
the increased backlog to the coordinator of this write. So for the
second write to observe the increased backlog, it needs to be coordinated
on the same node+shard as the first write.
We make sure that both writes are coordinated on the same node+shard by
using prepared statements combined with setting the host in `run_async`.
Both writes target the same partition and with prepared statements we
route them directly to the correct shard.
That was the idea, at least. In practice, for the driver to learn the
correct shard, it first needs to learn the token->shard mapping from
the server. For vnodes it can expect a shard by calculating the token
of the affected partition, but for tablets, it had no opportunity to
learn the tablet->shard mapping so the first write may route to any shard.
Additionally, we aren't guaranteed that the driver established connections
to all shards on all nodes at the point of any write. So if a connection
finishes establishing between the two writes, this may also cause us to
coordinate these 2 writes on different shards, leading to a missed view
backlog growth and not-rejected second write.
We fix this in this patch by running the test using one shard on each node.
This way, as long as we perform both writes on the same node, they'll also
be coordinated on the same shard. This also makes the prepared statement and
BoundStatement unnecessary — we can use SimpleStatement with
FallthroughRetryPolicy directly.
Fixes: SCYLLADB-1957
Closes scylladb/scylladb#29862
(cherry picked from commit f3cf20803b)
Closes scylladb/scylladb#29873
Closes scylladb/scylladb#29879
Scylla in-source tests.
For details on how to run the tests, see docs/dev/testing.md
Shared C++ utils, libraries are in lib/, for Python - pylib/
alternator - Python tests which connect to a single server and use the DynamoDB API unit, boost, raft - unit tests in C++ cqlpy - Python tests which connect to a single server and use CQL topology* - tests that set up clusters and add/remove nodes cql - approval tests that use CQL and pre-recorded output rest_api - tests for Scylla REST API Port 9000 scylla-gdb - tests for scylla-gdb.py helper script nodetool - tests for C++ implementation of nodetool
If you can use an existing folder, consider adding your test to it. New folders should be used for new large categories/subsystems, or when the test environment is significantly different from some existing suite, e.g. you plan to start scylladb with different configuration, and you intend to add many tests and would like them to reuse an existing Scylla cluster (clusters can be reused for tests within the same folder).
To add a new folder, create a new directory, and then
copy & edit its suite.ini.