Errors while running grafana-server with akumuli-datasource when !events not found

[igor-zacharov]

grafana 6.7.2 with akumuli-datasource 1.3.11.
I monitor the grafana log (/var/log/grafana/grafana.log) to find following messages after an update to simple graph request only if request for events is present and events are not found.
While these errors do poor in, the graph is still drawn on the screen.

Grafana.log:

t=2020-06-08T13:32:00+0200 lvl=eror msg="Data proxy error" logger=data-proxy-log userId=1 orgId=1 uname=admin path=/api/datasources/proxy/1/api/query remote_addr=172.21.0.254 referer="http://localhost:3002/d/6F7tvU1Z1/eurotech-summary-view?tab=queries&panelId=4&edit&fullscreen&orgId=1&from=now-5m&to=now&var-host=pcalc-10-A119K430001&var-samp=1m&var-process_name=All&var-uid=All" error="httputil: ReverseProxy read error during body copy: unexpected EOF"
t=2020-06-08T13:32:00+0200 lvl=eror msg="Request error" logger=context userId=1 orgId=1 uname=admin error="net/http: abort Handler"
t=2020-06-08T13:32:00+0200 lvl=eror msg="Data proxy error" logger=data-proxy-log userId=1 orgId=1 uname=admin path=/api/datasources/proxy/1/api/query remote_addr=172.21.0.254 referer="http://localhost:3002/d/6F7tvU1Z1/eurotech-summary-view?tab=queries&panelId=4&edit&fullscreen&orgId=1&from=now-5m&to=now&var-host=pcalc-10-A119K430001&var-samp=1m&var-process_name=All&var-uid=All" error="httputil: ReverseProxy read error during body copy: unexpected EOF"
t=2020-06-08T13:32:00+0200 lvl=eror msg="Request error" logger=context userId=1 orgId=1 uname=admin error="net/http: abort Handler"

The query to akumuli:

2020-06-08 13:41:03,289 [0x7f304bffe700] Main [INFO] Parsing query:
2020-06-08 13:41:03,289 [0x7f304bffe700] Main [INFO] {
"select-events": "!process",
"range": {
"from": "20200608T114041.798",
"to": "20200608T113541.798"
},
"where": {
"event": "start",
"host": "pcalc-10-A119K430001"
},
"order-by": "series",
"apply": "",
"limit": "1000000"
}

2020-06-08 13:41:03,300 [0x7f304f3fe700] http [INFO] Cursor 139845506879616 destroyed
2020-06-08 13:41:03,300 [0x7f304f3fe700] Main [TRACE] StorageSession is being closed
2020-06-08 13:41:03,394 [0x7f304bffe700] http [INFO] Cursor 139845523530264 created
2020-06-08 13:41:03,394 [0x7f304bffe700] http [INFO] Cursor 139845523530264 started
2020-06-08 13:41:03,395 [0x7f304f3fe700] Main [INFO] Parsing query:
2020-06-08 13:41:03,395 [0x7f304f3fe700] Main [INFO] {
"group-aggregate": {
"metric": "cpu.run",
"step": "2s",
"func": [
"max"
]
},
"range": {
"from": "20200608T114041.798",
"to": "20200608T113541.798"
},
"where": {
"host": "pcalc-10-A119K430001"
},
"order-by": "series",
"apply": "",
"limit": "1000000"
}
2020-06-08 13:41:03,395 [0x7f304f3fe700] Main [TRACE] Can't open next iterator because not found
..... 18 such messages....
2020-06-08 13:41:03,396 [0x7f304bffe700] http [INFO] Cursor 139845506879616 done
2020-06-08 13:41:03,396 [0x7f304bffe700] http [INFO] Cursor 139845506879616 destroyed
2020-06-08 13:41:03,396 [0x7f304bffe700] Main [TRACE] StorageSession is being closed

To say it again, if the !process query is not included (switch off on the grafana dashboard) there are no error messages in the grafana.log file. Also, there are no errors if the !process events are found.
Only if events are not found these errors in the grafana.log are present.

[Lazin]

It looks that grafana doesn't expect empty http response in case if there is no data. Not sure what should I do here since there is no results to send back to grafana. I'm going to ask grafana devs what the database should do in this case.