On 2017-11-29 18:17:18 +0100, Laurenz Albe wrote: > That is because the execution with the sequential scan touched > 26492 + 80492 = 106984 blocks, while the second execution touched > 311301 + 48510 = 359811 blocks, more than three times as many.
That's not necessarily said. What those count are buffer *accesses*, *not* the number of distinct blocks accessed. You'll very commonly have more buffer accesses in indexscans but still fewer total reads because a lot of those accesses will be reads previously done in the same scan. Just imagine a scan of an index with a leaf page pointing to 100 tuples of the same value - that'd result in at least a 100 buffer accesses, but it'd be highly likely that they'll be in cache. Greetings, Andres Freund
