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openstack-ansible/doc/source/install-guide/ops-galera-recoverycomplete.rst
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Change-Id: I3eedadc8ba441b4d931720dd6e3f7f3489302a9c
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Home OpenStack Ansible Installation Guide

Complete failure

If all of the nodes in a Galera cluster fail (do not shutdown gracefully), then the integrity of the database can no longer be guaranteed and should be restored from backup. Run the following command to determine if all nodes in the cluster have failed:

$ ansible galera_container -m shell -a "cat /var/lib/mysql/grastate.dat"
node3_galera_container-3ea2cbd3 | success | rc=0 >>
# GALERA saved state
version: 2.1
uuid:    338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno:   -1
cert_index:

node2_galera_container-49a47d25 | success | rc=0 >>
# GALERA saved state
version: 2.1
uuid:    338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno:   -1
cert_index:

node4_galera_container-76275635 | success | rc=0 >>
# GALERA saved state
version: 2.1
uuid:    338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno:   -1
cert_index:

All the nodes have failed if mysqld is not running on any of the nodes and all of the nodes contain a seqno value of -1.

If any single node has a positive seqno value, then that node can be used to restart the cluster. However, because there is no guarantee that each node has an identical copy of the data, it is not recommended to restart the cluster using the --wsrep-new-cluster command on one node.