Recall also that "committed deleted" does not mean "safe to remove". There may still be live transactions that could see the tuple. The "committed deleted" bit just exists to allow subsequent visitors to the row to skip one of the more expensive steps in deciding whether they can see it or not.
To determine that a row is removable requires additional tests above and beyond what backends normally do.
Aah - there is the first bullet hole in my multi-ctid-index-idea. Now the question becomes how expensive these tests are (if a normal backend can do them at all within reason)?
Jan
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