Re: compress method for spgist - 2

From: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
To: Teodor Sigaev <teodor(at)sigaev(dot)ru>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: compress method for spgist - 2
Date: 2014-12-23 09:48:38
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On 12/16/2014 07:48 PM, Teodor Sigaev wrote:
> /*
> * This struct is what we actually keep in index->rd_amcache. It includes
> * static configuration information as well as the lastUsedPages cache.
> */
> typedef struct SpGistCache
> {
> spgConfigOut config; /* filled in by opclass config method */
> SpGistTypeDesc attType; /* type of input data and leaf values */
> SpGistTypeDesc attPrefixType; /* type of inner-tuple prefix values */
> SpGistTypeDesc attLabelType; /* type of node label values */
> SpGistLUPCache lastUsedPages; /* local storage of last-used info */
> } SpGistCache;

Now that the input data type and leaf data type can be different, which
one is "attType"? It's the leaf data type, as the patch stands. I
renamed that to attLeafType, and went fixing all the references to it.
In most places it's just a matter of search & replace, but what about
the reconstructed datum? In freeScanStackEntry, we assume that
att[Leaf]Type is the datatype for reconstructedValue, but I believe
assume elsewhere that reconstructedValue is of the same data type as the
input. At least if the opclass supports index-only scans.

I think we'll need a separate SpGistTypeDesc for the input type. Or
perhaps a separate SpGistTypeDesc for the reconstructed value and an
optional decompress method to turn the reconstructedValue back into an
actual reconstructed input datum. Or something like that.

Attached is a patch with the kibitzing I did so far.

- Heikki

Attachment Content-Type Size
spgist_compress_method-4-heikki.patch text/x-diff 13.4 KB

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