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[Contrail] Schema Crash [ERROR]: Cassandra connection down. Exception in unbound method ColumnFamily.multiget



Article ID: KB36309 KB Last Updated: 10 Feb 2021Version: 1.0

This article provides the reason for a schema to crash in all nodes in Contrail and details the steps for resolution.


The Contrail schema is constantly crashing in all nodes with the following error in the contrail-schema logs.

11/02/2020 11:10:28 PM [contrail-schema] [WARNING]: RabbitMQ publish connection ESTABLISHED <Connection: amqp://guest:**@X.X.X.X:5672// at 0x7feeaa40f510>
11/02/2020 11:22:43 PM [contrail-schema] [ERROR]: Cassandra connection down. Exception in <unbound method ColumnFamily.multiget>
11/02/2020 11:22:43 PM [contrail-schema] [DEBUG]: Notification Message: {u'fq_name': [u'8a6f83bb-f156-40a4-b58f-3b6cd231543c'],
u'obj_dict': {u'display_name': u'8a6f83bb-f156-40a4-b58f-3b6cd231543c',
               u'fq_name': [u'8a6f83bb-f156-40a4-b58f-3b6cd231543c'],
               u'id_perms': {u'created': u'2020-11-02T23:10:40.237418',
                             u'creator': None,
                             u'description': None,
                             u'enable': True,
                             u'last_modified': u'2020-11-02T23:10:40.237418',
                             u'permissions': {u'group': u'cloud-admin-group',
                                              u'group_access': 7,
                                              u'other_access': 7,
                                              u'owner': u'cloud-admin',
                                              u'owner_access': 7},
                             u'user_visible': True,
                             u'uuid': {u'uuid_lslong': 9912825433908596324L,
                                       u'uuid_mslong': 14189465487881094428L}},
               u'perms2': {u'global_access': 0,
                           u'owner': u'cloud-admin',
                           u'owner_access': 7,
                           u'share': []},
               u'uuid': u'c4eb1bae-a5d1-451c-8991-6e3634944e64'},
u'oper': u'CREATE',
u'request-id': u'req-e1aafb9c-0bb3-44e0-8e80-fb2347942253',
u'type': u'virtual_machine',
u'uuid': u'c4eb1bae-a5d1-451c-8991-6e3634944e64'}
11/02/2020 11:22:43 PM [contrail-schema] [WARNING]: RabbitMQ drainer connection down



Even when Cassandra is up, Cassandra queries can time out if the timeout exception is raised more than max_retries. The MaximumRetryException exception is raised when this happens followed by the reporting of the "ERROR]: Cassandra connection down. Exception in <unbound method ColumnFamily.multiget>" log. Check the code at ‚Äč

To determine the cause, perform the following:

  1. Check the Contrail schema introspect for the process state of database Cassandra and Zookeeper by using the following URL:

http://<active schema node>:8087/Snh_SandeshUVECacheReq?x=NodeStatus

Look for any process that is listed as Non-Functional.

Note: The Contrail API queries through all the records, including tombstones (deleted records), before retrieving the list of VNs. A high number of tombstone cells can delay the list operation.

  1. In this case, the Cassandra errorlog (system.log) indicates a read query for 176915 tombstone cells due to which the API was timing out.



In order to resolve this issue, purge all tombstone records by setting gc_grace_second as 0. (Note: For detailed instructions, refer to KB35700 - [Contrail] Database: Cassandra connection down, IFMap Server End-Of-RIB not computed, No BGP configuration for self.)

For Cassandra config database:

  1. Enter into the container (config_database_cassandra_1).

Note: The container name may vary based on the different environments used for installation.

# docker exec -it config_database_cassandra_1 /bin/bash
  1. Connect to the Contrail config database.

# cqlsh <controller ip> 9041
Connected to contrail_database at X.X.X.X:9041.
  1. Check the current values:

cqlsh> SELECT table_name,gc_grace_seconds FROM system_schema.tables WHERE keyspace_name='config_db_uuid';

table_name        | gc_grace_seconds
obj_fq_name_table | 864000
obj_shared_table  | 864000
obj_uuid_table    | 864000
  1. Change the desired values to 0 seconds (for immediate purge):

cqlsh> ALTER TABLE config_db_uuid.obj_fq_name_table WITH gc_grace_seconds = 0;
cqlsh> ALTER TABLE config_db_uuid.obj_shared_table WITH gc_grace_seconds = 0;
cqlsh> ALTER TABLE config_db_uuid.obj_uuid_table WITH gc_grace_seconds = 0;
  1. Watch the Cassandra errorlogs (find / -name system.log) and wait for deletion of all tombstone records.

  2. Refer to KB35700 - [Contrail] Database: Cassandra connection down, IFMap Server End-Of-RIB not computed, No BGP configuration for self and set gc_grace_second as per environment needs.

  3. Restart the contrail-schema container in all the nodes and watch the contrail-schema.log for the re-initialization process.


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