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Use dedicated struct to represent nbtree insertion scan keys. Having a dedicated struct makes the difference between search type scankeys and insertion scankeys a lot clearer, and simplifies the signature of several related functions. This is based on a suggestion by Andrey Lepikhov. Streamline how unique index insertions cache binary search progress. Cache the state of in-progress binary searches within _bt_check_unique() for later instead of having callers avoid repeating the binary search in an ad-hoc manner. This makes it easy to add a new optimization: _bt_check_unique() now falls out of its loop immediately in the common case where it's already clear that there couldn't possibly be a duplicate. The new _bt_check_unique() scheme makes it a lot easier to manage cached binary search effort afterwards, from within _bt_findinsertloc(). This is needed for the upcoming patch to make nbtree tuples unique by treating heap TID as a final tiebreaker column. Unique key binary searches need to restore lower and upper bounds. They cannot simply continue to use the >= lower bound as the offset to insert at, because the heap TID tiebreaker column must be used in comparisons for the restored binary search (unlike the original _bt_check_unique() binary search, where scankey's heap TID column must be omitted). Author: Peter Geoghegan, Heikki Linnakangas Reviewed-By: Heikki Linnakangas, Andrey Lepikhov Discussion: https://postgr.es/m/CAH2-WzmE6AhUdk9NdWBf4K3HjWXZBX3+umC7mH7+WDrKcRtsOw@mail.gmail.com