Re: [HACKERS] TODO item: GUID
[EMAIL PROTECTED] wrote: ... I *like* sorting by time, as it allows the UUID to be used similar to sequence, leaving older, lesser accessed UUIDs in the past. and don't forget, an automatic timestamp of when a record is created might be useful for other purposes. Regards, Thomas Hallgren ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [HACKERS] TODO item: GUID
Hello, you just have to make random 128 bits and set version bits. And that's all. This is the way this data type is implemented in Mono ( http://svn.myrealbox.com/source/trunk/mcs/class/corlib/System/Guid.cs). Using time based GUIDs in database tables is not a good choice for performance reasons because they can not be indexed properly - every newly created time-based GUID is guaranteed to be larger than all previously created, so RDBMS engine must re balance b-tree every time a new GUID item is added to data table. Sorry, for sending this message three times - problem with Gmail.Cheers,Aleksandar Dezelin
Re: [HACKERS] TODO item: GUID
On Sat, Sep 09, 2006 at 07:47:19PM +0200, Aleksandar Dezelin wrote: Hello, you just have to make random 128 bits and set version bits. And that's all. This is the way this data type is implemented in Mono (http://svn.myrealbox.com/source/trunk/mcs/class/corlib/System/Guid.cs). Using time based GUIDs in database tables is not a good choice for performance reasons because they can not be indexed properly - every newly created time-based GUID is guaranteed to be larger than all previously created, so RDBMS engine must re balance b-tree every time a new GUID item is added to data table. Sorry, for sending this message three times - problem with Gmail. Depends how badly you want to skew the odds that a newly generated ID is actually new, and how much you trust the distribution of your random number generator. There are several ways to generate a UUID - and I think it is wrong to say that only one is the right way. Different applications choose different generation routines. I *like* sorting by time, as it allows the UUID to be used similar to sequence, leaving older, lesser accessed UUIDs in the past. You and Mono might prefer something else. Some choose random numbers over the MAC address as well - better? Depends on how big your system is. Cheers, mark -- [EMAIL PROTECTED] / [EMAIL PROTECTED] / [EMAIL PROTECTED] __ . . _ ._ . . .__. . ._. .__ . . . .__ | Neighbourhood Coder |\/| |_| |_| |/|_ |\/| | |_ | |/ |_ | | | | | | \ | \ |__ . | | .|. |__ |__ | \ |__ | Ottawa, Ontario, Canada One ring to rule them all, one ring to find them, one ring to bring them all and in the darkness bind them... http://mark.mielke.cc/ ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] TODO item: GUID
On Sat, Sep 09, 2006 at 07:47:19PM +0200, Aleksandar Dezelin wrote: Using time based GUIDs in database tables is not a good choice for performance reasons because they can not be indexed properly - every newly created time-based GUID is guaranteed to be larger than all previously created, so RDBMS engine must re balance b-tree every time a new GUID item is added to data table. Only if you have a particularly bad b-tree implementation. Do you also not believe in indexing timestamp or serial columns? regards, tom lane ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
[HACKERS] TODO item: GUID
I have two questions regarding the GUID todo item... 1. Do we want to have a new datatype for that or just a macro like the SERIAL type? create table bla ( my_pk GUID /* that is my_pk varchar(32) DEFAULT 'new_guid()' */ ) 2. Didn't we have a contrib module doing the GUID? Regards, Gevik. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] TODO item: GUID
On Tue, Sep 05, 2006 at 11:29:40AM +0200, Gevik Babakhani wrote: I have two questions regarding the GUID todo item... 1. Do we want to have a new datatype for that or just a macro like the SERIAL type? A new datatype. Just because someone has a guid column doesn't mean they want it autogenerated. Provide a generation function (not absolutly necessary) and you're done. Have a nice day, -- Martijn van Oosterhout kleptog@svana.org http://svana.org/kleptog/ From each according to his ability. To each according to his ability to litigate. signature.asc Description: Digital signature
Re: [HACKERS] TODO item: GUID
For developing the GUID datatype, I was wondering if I could use the sample code from http://www.ietf.org/rfc/rfc4122.txt (hate to reinvent the wheel) The code has a copyright which says: use and modify as you wish but include the copyright notice with your code What are our rules is such matters? Regards, Gevik. ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] TODO item: GUID
On Tue, Sep 05, 2006 at 02:29:15PM +0200, Gevik Babakhani wrote: For developing the GUID datatype, I was wondering if I could use the sample code from http://www.ietf.org/rfc/rfc4122.txt (hate to reinvent the wheel) The code has a copyright which says: use and modify as you wish but include the copyright notice with your code Do you really want to copy the code verbatim? I mean, there's a lot of stuff which would need quite a bit of massaging to get working in postgres. I'd say just look at it, understand it, and then write something that will work. The copyright won't matter then. BTW, I seem to remember something about the stuff in the RFC not being good for some reason, not unique enough or too predictable. Do you know anything about that? Have a nice day, -- Martijn van Oosterhout kleptog@svana.org http://svana.org/kleptog/ From each according to his ability. To each according to his ability to litigate. signature.asc Description: Digital signature
Re: [HACKERS] TODO item: GUID
Do you really want to copy the code verbatim? I mean, there's a lot of stuff which would need quite a bit of massaging to get working in postgres. I'd say just look at it, understand it, and then write something that will work. The copyright won't matter then. This is a better idea i must say. I will take a closer look at the code then see which parts I can reuse. BTW, I seem to remember something about the stuff in the RFC not being good for some reason, not unique enough or too predictable. Do you know anything about that? It was a privacy issue regarding GUID generation introduced by MS. The version 1 (V1) of the algorithm was created based on the MAC which was somehow back-traceable to the computer it was generated on I guess. Version 4 was based on a better algorithm. Have a nice day, ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
