Re: Revisiting {CREATE INDEX, REINDEX} CONCURRENTLY improvements

Hello, Sergey!

> I think it's to avoid duplicate errors when adding tuples from STIP to the main index,
> but couldn't we just suppress that error during validation and skip the new tuple insertion if it already exists?

In some cases, it is not possible:
– Some index types (GiST, GIN, BRIN) do not provide an easy way to
detect such duplicates.
– When we are building a unique index, we cannot simply skip
duplicates, because doing so would also skip the rows that should
prevent the unique index from being created (unless we add extra logic
for B-tree indexes to compare TIDs as well).

> The main index may get huge after building, and iterating over it in a single thread and then sorting tids can be
timeconsuming. 
My tests indicate that the overhead is minor compared with the time
spent scanning the heap and building the index itself.

> At least I guess one can skip it when STIP is empty.
Yes, that’s a good idea; I’ll add it later.

> p.s. I noticed that `stip.c` has a lot of functions that don't follow the Postgres coding style of return type on
separateline. 
Hmm... I’ll fix that as well.

Best regards,
Mikhail.