update:
The high load seems to be caused by invalid api key(username and password) from pmm-client side, I check the logs on the pmm-client side:
INFO[2023-09-27T01:17:51.297+00:00] 2023-09-27T01:17:51.297Z error VictoriaMetrics/app/vmagent/remotewrite/client.go:422 unexpected status code received after sending a block with size 40436 bytes to "1:secret-url" during retry #21: 401; response body="{\"code\":16,\"error\":\"invalid API key\",\"message\":\"invalid API key\"}\n"; re-sending the block in 60.000 seconds agentID=/agent_id/e19f9ad4-b27d-4fba-a821-1fb7302675a8 component=agent-process type=vm_agent
INFO[2023-09-27T01:17:51.299+00:00] 2023-09-27T01:17:51.299Z error VictoriaMetrics/app/vmagent/remotewrite/client.go:422 unexpected status code received after sending a block with size 40449 bytes to "1:secret-url" during retry #21: 401; response body="{\"code\":16,\"error\":\"invalid API key\",\"message\":\"invalid API key\"}\n"; re-sending the block in 60.000 seconds agentID=/agent_id/e19f9ad4-b27d-4fba-a821-1fb7302675a8 component=agent-process type=vm_agent
I do not know why after upgrading the pmm-client, it can not communicate with pmm-server correctly.
By the way, the database locked issue disappears after I add the following option to /etc/grafana/grafana.ini:
[database]
connection_string=file:/srv/grafana/grafana.db?cache=private&mode=rwc&_journal_mode=WAL
And after remove all pmm clients and reinstalled them, finally it return to normal.