"union" may be too memory intensive?

[klahnakoski]

Ensure there is a limit on the number of unique values in a union. The following may have overloaded the frontend node:

{
    "from": "unittest",
    "limit": 20,
    "select": {
        "aggregate": "union",
        "value": "build.platform"
    },
    "where": {
        "gt": {
            "run.timestamp": {
                "date": "today-day"
            }
        }
    }}

[klahnakoski]

WARNING: Could not process
{
	"from":"unittest",
	"limit":20,
	"select":{"aggregate":"union","value":"build.platform"},
	"meta":{"save":true}
}