Re: question on new psql datatype

Hello Yu Pu,

Am 2005-01-23 16:34:44, schrieb Yu Pan:
> I am developing a new "image" datatype in postgres which contains a binary
> field for storing image data and some other fields for additional information
> about the image, like size, resolution, etc. I was hoping that the clients can
> saving their time by directly retrieving these information from the fields
> without retrieving the whole image, that is, the time for reading these fields
> should be constant with respect to the image size. However, the result shows

Realy cool

> that the time for direct retrieving of information from the fields of an image
> datatype is still increasing with the size of the image. My explanation is
> that in order to read the fields of a image datatype, the whole struct would
> still need to be loaded into memory, which includes the binary field
> containing the actual image data. Can anyone tell me is this true for a user-
> defined datatype (using C struct)? Thanks a lot.

No, thats not right.

An Image is a Header (image type, width, height, rawsize, colortable)
plus the Data

In most cases the Header is between 20 and 300 Bytes
But which data do you need exactly ?

I have done this in Winword 6.0 under WfW 3.11 for 10 years :-)
You need only the first Bytes not the whole Image.

> Yu

Greetings
Michelle

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