Elizabeth Garrett Christensen: Postgres COUNT(DISTINCT) Too Slow? Fast Approximation Guide
💡原文英文，约4000词，阅读约需15分钟。
📝
内容提要
That's 320 milliseconds vs 671 ms for exact COUNT(DISTINCT) which is about twice as fast on a single scan. Also HLL isn't just about raw speed on one query. The function names are a bit verbose...
