This SQL error match with other tempest errors related to db connection:

ft36.8: tempest.scenario.test_network_v6.TestGettingAddress.test_slaac_from_os[compute,id-2c92df61-29f0-4eaa-bee3-7c65bef62a43,network,slow]testtools.testresult.real._StringException: pythonlogging:'': {{{
2022-03-17 19:24:08,805 201279 INFO     [tempest.lib.common.rest_client] Request (TestGettingAddress:setUp): 500 POST http://10.0.0.5:8774/v2.1/os-keypairs 0.015s
2022-03-17 19:24:08,805 201279 DEBUG    [tempest.lib.common.rest_client] Request - Headers: {'Content-Type': 'application/json', 'Accept': 'application/json', 'X-OpenStack-Nova-API-Version': '2.1', 'X-Auth-Token': '<omitted>'}
        Body: {"keypair": {"name": "tempest-TestGettingAddress-859199174", "public_key": "ecdsa-sha2-nistp384 AAAAE2VjZHNhLXNoYTItbmlzdHAzODQAAAAIbmlzdHAzODQAAABhBNyTQ4wV6HTMsdwTQzAUJ7DecjJ4+6JpCA3s0q7Cw+IJD7hImMHsmj1iOIa+OheCiiAq/dtRnWhFSTKDvX8zAyrpcUv3QtAzZ0TlBEtOKOh6hWJZ7Ni7+0PrCd+q1TFiiQ=="}}
    Response - Headers: {'date': 'Thu, 17 Mar 2022 23:24:08 GMT', 'server': 'Apache', 'content-length': '209', 'openstack-api-version': 'compute 2.1', 'x-openstack-nova-api-version': '2.1', 'vary': 'OpenStack-API-Version,X-OpenStack-Nova-API-Version', 'x-openstack-request-id': 'req-e85b9e92-e0a6-42cf-a49d-178e2d8b91c5', 'x-compute-request-id': 'req-e85b9e92-e0a6-42cf-a49d-178e2d8b91c5', 'content-type': 'application/json; charset=UTF-8', 'connection': 'close', 'status': '500', 'content-location': 'http://10.0.0.5:8774/v2.1/os-keypairs'}
        Body: b'{"computeFault": {"code": 500, "message": "Unexpected API Error. Please report this at http://bugs.launchpad.net/nova/ and attach the Nova API log if possible.\\n<class \'oslo_db.exception.DBConnectionError\'>"}}'
}}}

Traceback (most recent call last):
  File "/usr/lib/python3.9/site-packages/tempest/scenario/test_network_v6.py", line 68, in setUp
    self.keypair = self.create_keypair()
  File "/usr/lib/python3.9/site-packages/tempest/scenario/manager.py", line 179, in create_keypair
    body = client.create_keypair(**kwargs)
  File "/usr/lib/python3.9/site-packages/tempest/lib/services/compute/keypairs_client.py", line 91, in create_keypair
    resp, body = self.post("os-keypairs", body=post_body)
  File "/usr/lib/python3.9/site-packages/tempest/lib/common/rest_client.py", line 299, in post
    return self.request('POST', url, extra_headers, headers, body, chunked)
  File "/usr/lib/python3.9/site-packages/tempest/lib/services/compute/base_compute_client.py", line 47, in request
    resp, resp_body = super(BaseComputeClient, self).request(
  File "/usr/lib/python3.9/site-packages/tempest/lib/common/rest_client.py", line 703, in request
    self._error_checker(resp, resp_body)
  File "/usr/lib/python3.9/site-packages/tempest/lib/common/rest_client.py", line 879, in _error_checker
    raise exceptions.ServerFault(resp_body, resp=resp,
tempest.lib.exceptions.ServerFault: Got server fault
Details: Unexpected API Error. Please report this at http://bugs.launchpad.net/nova/ and attach the Nova API log if possible.
<class 'oslo_db.exception.DBConnectionError'>

But i did not see anything on mysql logs.

Checking the nova-compute service, i notice this:

/python3.9/site-packages/oslo_service/periodic_task.py:210
2022-03-17 23:23:10.814 2 ERROR oslo.messaging._drivers.impl_rabbit [req-a656b24b-ddcf-450c-84a2-27583e592954 - - - - -] [c11d0399-f03d-4fcf-9865-09584ccc3dff] AMQP server on overcloud-controller-0.internalapi.localdomain:5672 is unreachable: [Errno 104] Connection reset by peer. Trying again in 1 seconds.: ConnectionResetError: [Errno 104] Connection reset by peer
2022-03-17 23:23:11.004 2 ERROR oslo.messaging._drivers.impl_rabbit [-] [0055e02b-a50c-4688-a649-1e63e3b56e6d] AMQP server on overcloud-controller-0.internalapi.localdomain:5672 is unreachable: <RecoverableConnectionError: unknown error>. Trying again in 1 seconds.: amqp.exceptions.RecoverableConnectionError: <RecoverableConnectionError: unknown error>
2022-03-17 23:23:11.006 2 ERROR oslo.messaging._drivers.impl_rabbit [-] [949b296b-d736-4e0a-99a8-5177270052d1] AMQP server on overcloud-controller-0.internalapi.localdomain:5672 is unreachable: <RecoverableConnectionError: unknown error>. Trying again in 1 seconds.: amqp.exceptions.RecoverableConnectionError: <RecoverableConnectionError: unknown error>
2022-03-17 23:23:11.818 2 ERROR oslo.messaging._drivers.impl_rabbit [req-a656b24b-ddcf-450c-84a2-27583e592954 - - - - -] [c11d0399-f03d-4fcf-9865-09584ccc3dff] AMQP server on overcloud-controller-0.internalapi.localdomain:5672 is unreachable: [Errno 111] ECONNREFUSED. Trying again in 2 seconds.: ConnectionRefusedError: [Errno 111] ECONNREFUSED

In both nova-compute-1 and nova-compute-0 nodes