Re: Todo item: Support amgettuple() in GIN

On 11/29/2013 01:13 AM, Andreas Karlsson wrote:

> When doing partial matching the code need to be able to return the union
> of all TIDs in all the matching posting trees in TID order (to be able
> to do AND and OR operations with multiple search keys later). It does
> this by traversing them posting tree after posting tree and collecting
> them all in a TIDBitmap which is later iterated over.

I think it's not a plain union. My understanding is that - to evaluate a
single key (typically array) - you first need to get all the TID streams
for that key (i.e. one posting list/tree per element of the key array)
and then iterate all these streams in parallel and 'merge' them using
consistent() function. That's how I understand ginget.c:keyGetItem().

So the problem of partial match is (IMO) that there can be too many TID
streams to merge - much more than the number of elements of the key array.

// Antonin Houska (Tony)