| From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Cc: | Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: GIN improvements part 1: additional information |
| Date: | 2013-11-20 17:02:44 |
| Message-ID: | 528CEB34.7080702@vmware.com |
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| Thread: | |
| Lists: | pgsql-hackers |
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)
- Heikki
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