[ML] Memory estimate endpoint returns value less than 1MB minimum

[peteharverson]

Elasticsearch version: 8.0.0-SNAPSHOT

The endpoint used to provide an estimate of the model memory limit for a data frame analytics job /_ml/data_frame/analytics/_estimate_memory_usage can return values which are less than what appears to be the allowed 1MB minimum threshold.

For example, created a transform off the cloudwatch data set, with 80 docs (grouped by instance, and 6 aggregations), and the estimate for an outlier job is returned by the endpoint as 60kb. Following error is seen in the UI when attempting to run a job with this 60KB MML:

[elasticmachine]

Pinging @elastic/ml-core (:ml)

[przemekwitek]

The fix PR is merged to both master and 7.x.

Closing the issue.