David Helgason wrote:I'm switching right away. The notation doesn't really do anything for me, but that's fine. I've been using bit(128), but always suspected that of being unoptimal (for no particular reason).
I think bit(128) is quite efficient (OCTET_LENGTH() function shows me it's using 16 bytes).
Since I'm storing several big piles of data for each GUID, it's not ally an issue whether the storage is 16, 20, 22, 24, or 26 bytes, but thanks for the extensive guide. I've not gone over to using a GUID as PK+FK for the tables, and even if that should become interesting (for uniqueness across several databases for example), I would prefer a dual PK of (host-id, serial), where host-ids would be preassigned bit(8) values or some such.
I was mostly wondering about index efficiency and such. A bit of testing confirms that this seems to be just fine. Not that I'm surprised.
4. Ease of incremental searching. Suppose we're creating a GUI app to let user type in an item by its ID. VARCHAR(22) is a winner here since it allows users to type in normal characters in the keyboard and still lets Pg uses index for searching using "WHERE col LIKE '...%'".
However, most "sane" database design would use another unique code for most entities that need to be typed in. 128bit (22 characters as base64) are just too long anyway.
In my case, only applications ever specify the GUIDs, so this is a non-issue.
5. The ease of migrating to future "real GUID" datatype. I think using INET/CIDR will be easiest, as I can just use some simple combination of builtin Pg string function. But this is a very minor issue since if we're using a "real GUID" in the future, we most probably can't use our old GUID anymore, due to different creation algorithm.
I'm already using 'real' GUIDs, which in my case means that the database never generates them (since I don't have a generate_real_guid() function in the database (and don't need to).
Neither GUID project on gborg (mentioned in another thread) seem to be Mac OSX compatible, which is my current platform (but I want to stay more-or-less free of platform dependance just yet).
Howver, using INET/CIDR prevents me to use LIKE or ~. So I guess it's back to BYTEA for me.
Seems useless to me, since the GUIDS are practically random so LIKEness has no relevance.
So in short, for GUID I now tend to use BYTEA or INET/CIDR. Storing as base192/base64 feels a little wasteful for me, since I can use ENCODE(...) to display binary data as base64 anyway. I find BIT(n) awkward to work with/not properly supported in most languages.
I think I'll be staying with BIT(128) here, since none of the other really make anything easier. The INET might have been a choice, but it seems to have to much 'magic' in its output routines for me to feel comfortable around it.
However the client app uses a hex representation internally (don't tell me it's silly, it's already coded, due to intricacies of our project management), and my PL/PgSQL hex2bit() and bit2hex() functions are damn slow, so I'll be converting them to C any day not-so-soon (tried PL/Perl too, but even its simpler implementation was 5x slower yet !?)
d.
David Helgason Over the Edge Entertainments
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