Re: SPGist "triple parity" concept doesn't work

On Thu, Jun 6, 2013 at 10:46 PM, Tom Lane  wrote:
>  To prevent
> : deadlocks we introduce a concept of "triple parity" of pages: if inner tuple
> : is on page with BlockNumber N, then its child tuples should be placed on the
> : same page, or else on a page with BlockNumber M where (N+1) mod 3 == M mod 3.
> : This rule guarantees that tuples on page M will have no children on page N,
> : since (M+1) mod 3 != N mod 3.

Even if the invariant was maintained why doesn't that just mean you
need three concurrent inserts to create a deadlock?


-- 
greg