InfluxDB does not support datapoints without fields

[apfitzge]

Problem

• Influx does not support datapoints without fields
• We support sending datapoints without fields in our macros
• If you send a metric without fields it will cause all points batched with it to not be written to database

Proposed Solution

• Do not support writing datapoints with no fields through our macros

[apfitzge]

I wrote something to test this:

    loop {
        // datapoint_error!("datapoint-nofields");
        datapoint_error!("datapoint-withfields", ("field1", 5, i64));
        std::thread::sleep(std::time::Duration::from_secs(1));
    }

If I comment do not submit the datapoint-nofields I will see datapoint-withfields in my database.
If I do not comment it out, I see errors when writing the batches in MetricsAgent:

submit response unsuccessful: 400 Bad Request {"code":"invalid","message":"unable to parse 'datapoint-nofields,host_id=BioUwPnN7daq53JMTow8BRq6XGBz3djP4mKZCv6sAJct 1707333800103055331': invalid field format

[apfitzge]

Fields are a required piece of the InfluxDB data structure - you cannot have data in InfluxDB without fields.

• source - https://docs.influxdata.com/influxdb/v1/concepts/key_concepts/

[apfitzge]

I noticed this when searching for this metric:

datapoint_warn!("send_transaction_service-queue-overflow");

which I'd have expected to see since we see RPCs filling up their "queue" based on the separately submitted length counter.

This is probably causing us to lose some metrics submitted by RPCs, and was the only instance of a datapoint with no fields in our code (surprising!)