DBI-798: Safer check on mirror validation with MySQL sources setting server_id

[pfcoperez]

It adds a check on the utilization of the same server_id in the source MySQL server.
This offer an extra layer of protection against collisions with other replication actors.

[claude]

Code review

Found 1 issue. Checked for bugs and CLAUDE.md compliance.

Bug: nil pointer dereference at flow/cmd/validate_mirror.go:199

mysqlConn.Conn() returns nil at this call site, causing a panic inside HasReplicaWithServerId.

MySqlConnector uses lazy connection initialization. NewMySqlConnector stores conn as nil and never calls connect(). The actual TCP connection is only established on-demand via Execute()/withRetries(), which internally call connect().

Conn() is just c.conn.Load() — a bare atomic load that returns nil until a connection has been established. Since connectors.GetAs only calls the constructor (no queries), Conn() returns nil. HasReplicaWithServerId then calls conn.Execute(SHOW REPLICAS) on nil, which panics.

Suggested fix: Change HasReplicaWithServerId to accept the MySqlConnector (or a context + an interface with Execute) so it goes through the lazy-connect path, or trigger connection establishment before calling Conn().

See: NewMySqlConnector, Conn(), HasReplicaWithServerId

[jgao54]

nit: can avoid an extra connect/disconnect by moving mysql_validation.HasReplicaWithServerId inside ValidateMirrorSource and pass in an already instantiated conn, although i understand that having this here put server_id validation check together. Your call.

[codecov]

❌ 4 Tests Failed:

Tests completed	Failed	Passed	Skipped
3041	4	3037	371

View the top 3 failed test(s) by shortest run time

github.com/PeerDB-io/peerdb/flow/e2e::TestApiMariaDB

Stack Traces | 0.01s run time

=== RUN   TestApiMariaDB
=== PAUSE TestApiMariaDB
=== CONT  TestApiMariaDB
--- FAIL: TestApiMariaDB (0.01s)
2026/07/10 18:27:35 INFO Received AWS credentials from peer for connector: ci x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}
2026/07/10 18:27:35 INFO Received AWS credentials from peer for connector: clickhouse x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}

github.com/PeerDB-io/peerdb/flow/e2e::TestApiMy

Stack Traces | 0.02s run time

=== RUN   TestApiMy
=== PAUSE TestApiMy
=== CONT  TestApiMy
--- FAIL: TestApiMy (0.02s)
2026/07/10 18:32:53 INFO Received AWS credentials from peer for connector: ci x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}
2026/07/10 18:32:53 INFO Received AWS credentials from peer for connector: clickhouse x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}

github.com/PeerDB-io/peerdb/flow/e2e::TestApiMy/TestValidateCDCMirror_ServerIDPeerReuse

Stack Traces | 0.05s run time

=== RUN   TestApiMy/TestValidateCDCMirror_ServerIDPeerReuse
=== PAUSE TestApiMy/TestValidateCDCMirror_ServerIDPeerReuse
=== CONT  TestApiMy/TestValidateCDCMirror_ServerIDPeerReuse
2026/07/10 18:31:25 INFO Received AWS credentials from peer for connector: ci x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}
2026/07/10 18:31:25 INFO Received AWS credentials from peer for connector: clickhouse x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}
    api_test.go:381: 
        	Error Trace:	.../flow/e2e/api_test.go:381
        	Error:      	Received unexpected error:
        	            	rpc error: code = Internal desc = internal server error
        	Test:       	TestApiMy/TestValidateCDCMirror_ServerIDPeerReuse
    api_test.go:51: begin tearing down postgres schema api_evlgjbe7
2026/07/10 18:31:25 INFO fetched schema x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN} table=e2e_test_mych_yawdnspt.test_bit
--- FAIL: TestApiMy/TestValidateCDCMirror_ServerIDPeerReuse (0.05s)

github.com/PeerDB-io/peerdb/flow/e2e::TestApiMariaDB/TestValidateCDCMirror_ServerIDPeerReuse

Stack Traces | 0.06s run time

=== RUN   TestApiMariaDB/TestValidateCDCMirror_ServerIDPeerReuse
=== PAUSE TestApiMariaDB/TestValidateCDCMirror_ServerIDPeerReuse
=== CONT  TestApiMariaDB/TestValidateCDCMirror_ServerIDPeerReuse
2026/07/10 18:26:00 INFO Received AWS credentials from peer for connector: ci x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}
2026/07/10 18:26:00 INFO Received AWS credentials from peer for connector: clickhouse x-peerdb-additional-metadata={Operation:FLOW_OPERATION_UNKNOWN}
    api_test.go:381: 
        	Error Trace:	.../flow/e2e/api_test.go:381
        	Error:      	Received unexpected error:
        	            	rpc error: code = Internal desc = internal server error
        	Test:       	TestApiMariaDB/TestValidateCDCMirror_ServerIDPeerReuse
    api_test.go:51: begin tearing down postgres schema api_umm4t365
--- FAIL: TestApiMariaDB/TestValidateCDCMirror_ServerIDPeerReuse (0.06s)

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[github-actions]

❌ Test Failure

Analysis: The PR's own new test TestValidateCDCMirror_ServerIDPeerReuse fails deterministically across all three MySQL matrix jobs with an "internal server error" RPC response, indicating a real bug in the new server_id validation code rather than a flaky/timing/network issue.
Confidence: 0.94

⚠️ This appears to be a real bug - manual intervention needed

View workflow run

[jgao54]

(pending integrations test fixes)