Use ExecutedGtidSet and RetrievedGtidSet when determining the primary

[d-kuro]

refs: #370

Use Executed_Gtid_Set and Retrieved_Gtid_Set when determining the primary.

Previously, only Retrieved_Gtid_Set was used to select the primary.
However, there are cases where Retrieved_Gtid_Set is empty immediately after replication starts if there are no new transactions.

$ kubectl-moco mysql test --index 2 -- -e "SHOW REPLICA STATUS\G"
*************************** 1. row ***************************
             Replica_IO_State: Waiting for source to send event
...
           Retrieved_Gtid_Set:
            Executed_Gtid_Set: 09a2bf6a-960c-11ec-bf89-9ee9543e8238:1,
09c0848a-960c-11ec-90e9-0a55db88221e:1-4
...

Therefore, change to also use ExecutedGtidSet for finding primary.

// There are cases where Retrieved_Gtid_Set is empty,
// such as when there is no transaction immediately after a fail-over.
// Therefore, Retrieved_Gtid_Set and Executed_Gtid_Set are unioned to find for the top runner.
// The union of two GTID sets is simply their joined together with an interposed comma.
// https://dev.mysql.com/doc/refman/8.0/en/gtid-functions.html
var gtids string
if len(repl.RetrievedGtidSet) == 0 {
	gtids = repl.ExecutedGtidSet
} else {
	gtids = fmt.Sprintf("%s,%s", repl.RetrievedGtidSet, repl.ExecutedGtidSet)
}

Steps

1. Submitting data

$ kubectl-moco mysql test -it -u moco-writable -- -e "CREATE DATABASE test;"
$ kubectl-moco mysql test -it -u moco-writable -- -e "CREATE TABLE test.t1 (foo int);"
$ kubectl-moco mysql test -it -u moco-writable -- -e "INSERT INTO test.t1 (foo) VALUES (1); COMMIT;"

2. Kills the primary and causes failover

$ kubectl get mysqlcluster test
$ PRIMARY=$(kubectl get mysqlcluster test -o jsonpath='{.status.currentPrimaryIndex}')
$ kubectl exec -it moco-test-${PRIMARY} -c mysqld -- kill 1

3. Kill the primary again

$ PRIMARY=$(kubectl get mysqlcluster test -o jsonpath='{.status.currentPrimaryIndex}')
$ kubectl exec -it moco-test-${PRIMARY} -c mysqld -- kill 1

4. The following log is output and failover fails

{"level":"error","ts":1646976101.8021455,"logger":"cluster-manager.default/test","msg":"error","error":"failed to failover: failed to choose the next primary: unable to determine the top runner"}

[masa213f]

The value of currentPrimaryIndex is out of date here.
Could you update currentPrimaryIndex after line 104?

[d-kuro]

Thank you for the review. I fixed the issue as it was not correctly evaluating. Thank you again.

c823871

[masa213f]

LGTM