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We add reproducing tests for two known Alternator issues, #6391 and #9868, which involve the non-atomicity of table creation. Creating a table currently involves multiple steps - creating a keyspace, a table, materialized views, and tags. If some of these steps succeed and some fail, we get an InternalServerError and potentially leave behind some half-built table. Both issues will be solved by making better use of the new Raft-based capabilities of making multiple modifications to the schema atomically, but this patch doesn't fix the problem - it just proves it exist. The new tests involve two threads - one repeatedly trying to create a table with a GSI or with tags - and the other thread repeatedly trying to delete the same table under its feet. Both bugs are reproduced almost immediately. Note that like all test/alternator tests, the new tests are usually run on just one node. So when we fix the bug and these tests begin to pass, it will not be a proof that concurrent schema modification works safely on *different* nodes. To prove that, we will also need a multi-node test. However, this test can prove that we used Raft-based schema modification correctly - and if we assume that the Raft-based schema modification feature is itself correct, then we can be sure that CreateTable will be correct also across multiple nodes. Although it won't hurt to check it directly. Refs #6391 Refs #9868 Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20220207223100.207074-1-nyh@scylladb.com>