Re: GIN improvements part 1: additional information

On Tue, Nov 26, 2013 at 5:34 PM, Alexander Korotkov <aekorotkov(at)gmail(dot)com>wrote:

> On Wed, Nov 20, 2013 at 9:02 PM, Heikki Linnakangas <
> hlinnakangas(at)vmware(dot)com> wrote:
>
>> On 06.11.2013 17:36, Alvaro Herrera wrote:
>>
>>> Just for my own illumination, can someone explain this bit?
>>>
>>> + If a posting list is too large to store in-line in a key entry, a
>>> posting tree
>>> + is created. A posting tree is a B-tree structure, where the
>>> ItemPointer is
>>> + used as the key. At the leaf-level, item pointers are stored
>>> compressed, in
>>> + "varbyte encoding".
>>>
>>> I think the first ItemPointer mentioned (the key) refers to a TID
>>> pointing to the index, and "item pointers stored compressed" refers to
>>> the TIDs pointing to the heap (the data). Is that correct?
>>>
>>
>> No, they both refer to TIDs pointing to the heap.
>>
>>
>> I'm also interested in the "FIXME explain varbyte encoding" explanation
>>> currently missing, if somebody can write it down ...
>>>
>>
>> Alexander's latest version filled in that explanation (haven't read it
>> myself yet)
>
>
> off-list
>

It appears to be not actually off-list, sorry :)

> What's your plans about GIN now? I tried to rebase packed posting lists
> with head. But I found that you've changed interface of placeToPage
> function. That's conflicts with packed posting lists, because
> dataPlaceToPageLeaf needs not only offset number to describe place to
> insert item pointer. Do you like to commit rework of handling GIN
> incomplete splits before?
>

------
With best regards,
Alexander Korotkov.