It does, and has since its original discovery. Though the effect is not as pronounced as its popular conception would have you believe. The poor performers overrated their performance, but did not rate it higher than the high performers did. It is more like the grandparent observed that everyone tends to think of themselves as close to average.
Databases aren't my field, but I would expect this to hurt performance by decreasing locality of keys.
This, of course, assumes that temporally-adjacent additions are related, but this seems like a common case for large data sets since they often arise from a series of measurements or transactions.
I created this account to make this reply because I imagine that someone here is expert enough to set me straight if I'm mistaken.
class Bottom { private: Bottom(){} };