presto-main/src/main/java/io/prestosql/operator/aggregation/builder/SpillableHashAggregationBuilder.java/SpillableHashAggregationBuilder/shouldMergeWithMemory
class SpillableHashAggregationBuilder:    private boolean shouldMergeWithMemory(long memorySize)
    {
        return memorySize < memoryLimitForMergeWithMemory;
    }