Re: inet versus text for ip addresses

Dan Langille wrote:
> The PostgreSQL inet datatype stores an holds an IP host address, and
> optionally the identity of the subnet it is in, all in one field.
> This requires 12 bytes.
>
> Using my "random" data of approximately 8000 IP addresses collected
> during previous polls, I've found the average length of an IP address
> is 13.1 bytes. An integer requires 4 bytes.
>
> First question: Why not store an option to store just an IP address?
> That should require less than the 12 bytes for inet.

We store inet and cidr in similar structures, and they are of variable
length (4 byte overhead):

/*
* This is the internal storage format for IP addresses
* (both INET and CIDR datatypes):
*/
typedef struct
{
unsigned char family;
unsigned char bits;
unsigned char type;
union
{
unsigned int ipv4_addr; /* network byte order */
/* add IPV6 address type here */
} addr;
} inet_struct;

/*
* Both INET and CIDR addresses are represented within Postgres as varlena
* objects, ie, there is a varlena header (basically a length word) in front
* of the struct type depicted above.
*
* Although these types are variable-length, the maximum length
* is pretty short, so we make no provision for TOASTing them.
*/
typedef struct varlena inet;

In 7.4, we support IPv6, so they will be even larger.

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