1. Table AM with a 6-byte TID.
2. Table AM with a custom locator format, which could be TID-like.
3. Table AM with no locators.

Currently TID has its own type in system catalog. Seems, it's possible that storage claims type of TID which it uses. Then, AM could claim it too, so the core based on that information could solve the question about AM-storage compatibility. Storage could also claim that it hasn't TID type at all so it couldn't be used with any access method, use case: compressed column oriented storage.

As I remeber, only GIN depends on TID format, other indexes use it as opaque type. Except, at least, btree and GiST - they believ that internal pointers are the same as outer (to heap)

Another dubious part - BitmapScan.

Teodor Sigaev                                   E-mail: teo...@sigaev.ru
                                                   WWW: http://www.sigaev.ru/

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