Suspicious persists during the ingestion

### Affected Version

0.17, 0.18

### Description

```
2020-05-29T19:39:41,325 INFO [[index_kinesis_events_f3f78b11e73489e_cpmeplam]-appenderator-persist] org.apache.druid.segment.realtime.appenderator.AppenderatorImpl - Flushed in-memory data for segment[events_2020-05-29T17:00:00.000Z_2020-05-29T18:00:00.000Z_2020-05-29T17:00:00.217Z_58] spill[12] to disk in [2,861] ms (99,998 rows).
2020-05-29T19:39:41,354 INFO [[index_kinesis_events_f3f78b11e73489e_cpmeplam]-appenderator-persist] org.apache.druid.segment.realtime.appenderator.AppenderatorImpl - Flushed in-memory data for segment[events_2020-05-29T16:00:00.000Z_2020-05-29T17:00:00.000Z_2020-05-29T16:00:00.435Z_378] spill[9] to disk in [10] ms (2 rows).
...
```

Observed this pattern of persists was repeatedly happening when `maxRowsInMemory` was 100,000. `maxTotalRows` was default.

Start with AppenderatorImpl and the ingestion settings shown in the report, especially maxRowsInMemory and maxTotalRows; compare the repeated persist log entries with the expected ingestion behavior. Done means determining whether the persists are erroneous and, if so, defining a reproducible failure and regression coverage.

Written by the indexing model from the issue text.