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This patch adds a test for issue #18719: Although the Alternator TTL
work is supposedly done in the "streaming" scheduling group, it turned
out we had a bug where work sent on behalf of that code to other nodes
failed to inherit the correct scheduling group, and was done in the
normal ("statement") group.
Because this problem only happens when more than one node is involved,
the test is in the multi-node test framework test/topology_experimental_raft.
The test uses the Alternator API. We already had in that framework a
test using the Alternator API (a test for alternator+tablets), so in
this patch we move the common Alternator utility functions to a common
file, test_alternator.py, where I also put the new test.
The test is based on metrics: We write expiring data, wait for it to expire,
and then check the metrics on how much CPU work was done in the wrong
scheduling group ("statement"). Before #18719 was fixed, a lot of work
was done there (more than half of the work done in the right group).
After the issue was fixed in the previous patch, the work on the wrong
scheduling group went down to zero.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
(cherry picked from commit 1fe8f22d89)
Modifications in the cherry-pick:
* Moved test to topology_custom directory, so it runs without tablets
* use the server_add() function instead of the newer add_servers() which
didn't yet exist in this branch.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>