[WIP] Fix infinite retry issue when a host fails with server error

[Copilot]

Fix infinite retry when a single host fails with server error

Plan:

• Understand the issue: when _make_query_plan() sets query_plan to a list [self._host] instead of an iterator, subsequent retries iterate the list from the beginning, causing infinite retries
• Fix the bug by converting the single-host list to an iterator in _make_query_plan() method
• Create unit test to verify the fix prevents infinite retries with single host
• Run existing tests to ensure no regressions
• Run code review and security checks

Original prompt

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This section details on the original issue you should resolve

<issue_title>infinite retry when a single host fails with server error</issue_title>
<issue_description>When executing a query on a single host with the default retry policy, if the query fails with a server error, the query is retried infinitely and without delays.

Consider this simple test:

    servers = await manager.servers_add(1, auto_rack_dc="dc1")
    cql, hosts = await manager.get_ready_cql(servers)
    async with new_test_keyspace(manager, "WITH replication = {'class': 'NetworkTopologyStrategy', 'replication_factor': 1}") as ks:
        await cql.run_async(f"CREATE TABLE {ks}.t2 (pk int, ck int, v int, PRIMARY KEY (pk, ck))")
        await manager.api.enable_injection(servers[0].ip_addr, "fail_mutate_internal", one_shot=False)
        await cql.run_async(f"INSERT INTO {ks}.t2(pk, ck, v) VALUES(0,0,0)")

the query fails immediately with NoHostAvailable exception:

>           await cql.run_async(f"INSERT INTO {ks}.t2(pk, ck, v) VALUES(0,0,0)")
E           cassandra.cluster.NoHostAvailable: ('Unable to complete the operation against any hosts', {<Host: 127.193.50.1:9042 dc1>: <Error from server: code=0000 [Server error] message="Error injection in mutate_internal">})

However, suppose we change the query to run on a specific host with host=hosts[0]:

        await cql.run_async(f"INSERT INTO {ks}.t2(pk, ck, v) VALUES(0,0,0)", host=hosts[0])

now we see infinite Server error logs:

11:16:34.820 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.820 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.820 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.821 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.821 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.822 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.822 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.822 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.823 WARNING>  Host 127.99.46.1:9042 error: Server error.
11:16:34.823 WARNING>  Host 127.99.46.1:9042 error: Server error.

I suspect the problem is that in send_request it expects query_plan to be an iterator, but in make_query_plan if there is a single host then it creates a list.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes infinite retry when a single host fails with server error #534

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