Re: Alternative variable length structure

I assume the conclusion from this email thread is that though the idea
is interesting, the complexity added would not be worth the saving of a
few bytes.

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ITAGAKI Takahiro wrote:
> Hi Hackers,
>
> PostgreSQL can treat variable-length data flexibly, but therefore
> it consumes more spaces if we store short data. Headers of
> variable-length types use 4 bytes regardless of the data length.
>
> My idea is to change the header itself to variable-length.
> In order to reduce the size of short data, I wrote a patch to encode
> lengths into the first several bits of structure. Also, the alignments
> of the types were changed to 'char' from 'int'.
>
>
> I know my patch is still insufficient, for example, the types cannot
> be TOASTed. But I guess this compression works well for short text.
>
> I'll appreciate any comments.
> thanks.
>
>
> ---- the result of patch ----
>
> # create table txttbl (v1 text, v2 text, v3 text, v4 text);
> # create table strtbl (v1 string, v2 string, v3 string, v4 string);
>
> # insert into txttbl values('A', 'B', 'C', 'D');
> # insert into strtbl values('A', 'B', 'C', 'D');
>
> # select * from pgstattuple('txttbl');
> -[ RECORD 1 ]------+------
> table_len | 8192
> tuple_count | 1
> tuple_len | 57 <-- 28 + (5+3) + (5+3) + (5+3) + (5)
> ...
>
> # select * from pgstattuple('strtbl');
> -[ RECORD 1 ]------+------
> table_len | 8192
> tuple_count | 1
> tuple_len | 36 <-- 28 + 2 + 2 + 2 + 2
> ...
>
> ---
> ITAGAKI Takahiro
> NTT Cyber Space Laboratories

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