Re: RFD: hexstring(n) data type - Mailing list pgsql-hackers

I am confused how a hex type is any better than using the 'hex' decode()
format we already support:
test=> select decode('5476', 'hex'); decode-------- Tv(1 row)

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Dawid Kuroczko wrote:
> Following the discussion on making UUID data type to be much more liberal
> ( http://archives.postgresql.org/pgsql-hackers/2008-02/msg01214.php )
> I have decided to try to approach it from more general perspective.
> 
> The current state of code is available at:
> http://qnex.net/hexstring-0.1-2008-03-03.tgz
> 
> 
> And now for more details:
> 
> The idea is to have a data type HEXSTRING(n) which can have an optional
> typemod specifying the size of data (in bytes).
> 
> Internally the datatype is binary compatible with bytea, but I/O is done as
> hex-encoded strings.  The format is liberal, isspace() and ispunct() characters
> are skipped while the digits are read.
> 
> I have played with two versions of hexstringin() function, one which uses
> strtoul() function and the other which uses "home brew" code.  The latter
> appears to be faster, so I stayed with that.  But I would appreciate
> comments on this from more experienced.
> 
> So, what are the use cases?
> 
> CREATE DOMAIN liberal_uuid AS hexstring(16);
> CREATE DOMAIN liberal_macaddr AS hexstring(6);
> 
> ...it allows for creating other standard hex-types, as for example:
> CREATE DOMAIN wwn AS hexstring(8); --
> http://en.wikipedia.org/wiki/World_Wide_Name
> 
> Also it can be a convenient alternative to bytea format (I know, the
> encode()/decode() pair),
> especially when you have to format output data as some fancy hex-string.
> 
> The code is currently just a bunch of input/output/typemod functions
> which appear
> to work.  I will add casts, operators, etc -- they most likely will be
> nicked from bytea.
> 
> What I would like to also add is ubiquitous to_char(hex, format) function.
> For an UUID-compatilbe format it would be called as:
> SELECT to_char(hex, 'xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx') or
> SELECT to_char(hex, '8x-4x-4x-4x-12x') where x is expanded as
> [0-9a-f] digit and X is expanded as [0-9A-F].
> I am not sure what to do about variable length hexstrings, I am
> considering something
> like to_char(hex, '8X-') which would produce something like
> '00000000-11111111-22222222'
> for a 12-byte hexstring (what to do about dangling '-' ?).
> 
> ...but the original case against liberal UUID was that it would make
> the I/O slower.
> My simple test:
> 
> postgres=# CREATE TABLE uuids AS SELECT uuid_generate_v4()::text AS u
> FROM generate_series(1,10000000);
> CREATE
> 
> postgres=# CREATE TEMP TABLE text ON COMMIT DROP AS SELECT
> u::hexstring(16) FROM uuids;
> SELECT
> Time: 13058.486 ms
> postgres=# CREATE TEMP TABLE test ON COMMIT DROP AS SELECT u::uuid FROM uuids;
> SELECT
> Time: 13536.816 ms
> 
> ...now hexstring is varlena type but does not use strtoul.  Perhaps
> uuid might be more liberal too.
> 
> What do you think about it?
> 
>    Regards,
>      Dawid
> 
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