Re: [HACKERS] Varlena Type Creation
Le mercredi 27 février 2008, Martijn van Oosterhout a écrit : I see no-one responded to this: a varlena has no fixed header size, so you can't fit it in a structure anyway. Once you're passed a pointer you use the LEN/PTR macros to extract what you want. Once the type exists and the code gets some varlena kind type of objects to play with, I think I'll use the same macros as for text usage... My problem is more how to define a new composite varlena, that is a new varlena type composed of several base type... I'm not sure I'm using a good vocabulary, please forgive me if it's all unclear... Not sure what the chars are for Maybe the input syntax would help getting what the chars are for. To say a prefix range begins with '012' and any entry between '3' and '6', you'd write e.g. '012[3-6]'::prefix_range. The chars are respectively '3' and '6' and the greatest prefix of the prefix range is '012' here. Here, '012[3-6]' @ '01234' is true but '012[3-6]' @ '0122' is false. , but perhaps it would be easiest to treat it as a single text object with the two leading characters signifying something? I like your idea of using a single text datum for this and encode into it the information I need: it makes it all simple for me to start working. But still does not answer the question... not that the answer is needed any more... Thanks, -- dim signature.asc Description: This is a digitally signed message part.
Re: [HACKERS] Varlena Type Creation
On Tue, Feb 26, 2008 at 06:19:48PM +0100, Dimitri Fontaine wrote: So... where do I start to create a varlena datatype which has to store the 3 following values: text prefix, char start, char end. It's not clear for me whether this is what I need to provide: typedef struct I see no-one responded to this: a varlena has no fixed header size, so you can't fit it in a structure anyway. Once you're passed a pointer you use the LEN/PTR macros to extract what you want. Not sure what the chars are for, but perhaps it would be easiest to treat it as a single text object with the two leading characters signifying something? Have a nice day, -- Martijn van Oosterhout [EMAIL PROTECTED] http://svana.org/kleptog/ Those who make peaceful revolution impossible will make violent revolution inevitable. -- John F Kennedy signature.asc Description: Digital signature
[HACKERS] Varlena Type Creation
Hi,
I'm working on a GiST opclass to support prefix searching as presented here:
http://pgsql.tapoueh.org/site/html/prefix/index.html
http://prefix.projects.postgresql.org/README.html
http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/prefix/prefix/
In order to have a much more efficient index, I received the advice to
implement a prefix range datatype then base the picksplit() and union()
implementation on top of it.
So... where do I start to create a varlena datatype which has to store the 3
following values: text prefix, char start, char end.
It's not clear for me whether this is what I need to provide:
typedef struct
{
int32 vl_len_;
charstart;
charend;
textprefix;
} prefix_range;
In particular, I've been taught a varlena definition can not contain pointers,
and I've no idea how to embed a text into another varlena...
Regards,
--
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