"normal" vacuum basically skips both all-frozen and all-visible pages.
aggressive vacuum scans all-visible pages, but skips all-frozen ones.
Right?
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That's correct, but I prefer this definition: An aggressive VACUUM is guaranteed to be able to advance relfrozenxid to a recent value. Non-aggressive advances relfrozenxid on a "best effort" basis, though it can visit a *small* number of all-vis pages to make it more likely.
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I think that we should make non-aggressive more like aggressive in the future -- it can be clever about doing just a little more work to advance relfrozenxid sooner. So I prefer my abstract "aggressive" definition because it remains valid even after VACUUM is taught all this.