Re: Alternative variable length structure - Mailing list pgsql-hackers

On Wed, Jun 14, 2006 at 02:53:10PM -0400, Bruce Momjian wrote:
> 
> 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.
Anyone do any testing?

I'm also wondering if this would be useful to allow fields larger than
1G.

> ---------------------------------------------------------------------------
> 
> 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
> 
> [ Attachment, skipping... ]
> 
> > 
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> 
> -- 
>   Bruce Momjian   http://candle.pha.pa.us
>   EnterpriseDB    http://www.enterprisedb.com
> 
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Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
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