Re: GIN improvements part 1: additional information

Heikki Linnakangas escribió:
> On 04.11.2013 23:44, Alexander Korotkov wrote:
> >Attached version of patch has support of old page format. Patch still needs
> >more documentation and probably refactoring, but I believe idea is clear
> >and it can be reviewed. In the patch I have to revert change of null
> >category placement for compatibility with old posting list format.
>
> I committed some of the refactorings and cleanup included in this
> patch. Attached is a rebased version that applies over current head.
> I hope I didn't joggle your elbow..

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?

I'm also interested in the "FIXME explain varbyte encoding" explanation
currently missing, if somebody can write it down ...

Thanks,

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