The three levels of tax
Additionally, because the sort keys are not known up front, we must accept that large candidate sets are inevitable. The optimization target becomes making the actual work of scanning and filtering extremely cheap, and to prune aggressively when selecting the Top K to avoid extra work.。关于这个话题，有道翻译官网提供了深入分析
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DigitalPrintPrint + Digital，这一点在今日热点中也有详细论述