New feature: cached foreign keys

Hi.

Today i have an idea for increase performance of foreign keys. After
search parent record, store ctid in shared memory. Subsequent searches
look first to the record at stored ctid, and when it is deleted do
regular search using index.

Pro: faster searching for common keys when parent table is constant.
Less locks on index.

Contra: slower searching when parent table is heavy updated. More
memory used for cached ctid's.



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pasman