Re: Todo item: Support amgettuple() in GIN

On 11/29/2013 01:57 PM, Andreas Karlsson wrote:
> On 11/29/2013 09:54 AM, Antonin Houska wrote:
>> 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().
>
> For partial matches the merging is done in two steps: first a simple
> union of all the streams per key and then second merging those union
> streams using the consistent() function.

Yes, short after I sent my previous mail I realized that your "union"
probably referred to the things that collectMatchBitmap() does.

// Tony