We neither hate nor love UUIDs, but we like them when they provide value
and we also accept alternatives. What we do hate is ambiguity and in
certain cases UUIDs help.
Look at the hrefs returned in this sample resource and picture what
you'd store in your database as unique identifier to refer to each one:
{"server"=>
{"name"=>"kd_test_3",
"flavorRef"=>"http://5.5.2.2:8774/v1.1/flavors/3
<http://50.56.22.22:8774/v1.1/flavors/3>",
"addresses"=>
{"public"=>[], "private"=>[{"version"=>4, "addr"=>"5.5.2.5"}]},
"metadata"=>{"v2"=>"d2", "4"=>"14", "5"=>"17"},
"imageRef"=>"http:// <http://50.56.22.22:8774/v1.1/images/1>5.5.2.2
<http://50.56.22.22:8774/v1.1/flavors/3>:8774/v1.1/images/1
<http://50.56.22.22:8774/v1.1/images/1>",
"id"=>26,
"hostId"=>"4e6200284bc7bd28e49016aa047fbdc6a3f5",
"links"=>
[{"href"=>"http:// <http://50.56.22.22:8774/v1.1/servers/26>5.5.2.2
<http://50.56.22.22:8774/v1.1/flavors/3>:8774/v1.1/servers/26
<http://50.56.22.22:8774/v1.1/servers/26>", "rel"=>"self"},
{"href"=>"http:// <http://50.56.22.22:8774/v1.1/servers/26>5.5.2.2
<http://50.56.22.22:8774/v1.1/flavors/3>:8774/v1.1/servers/26
<http://50.56.22.22:8774/v1.1/servers/26>",
"rel"=>"bookmark",
"type"=>"application/json"
},
{"href"=>"http:// <http://50.56.22.22:8774/v1.1/servers/26>5.5.2.2
<http://50.56.22.22:8774/v1.1/flavors/3>:8774/v1.1/servers/26
<http://50.56.22.22:8774/v1.1/servers/26>",
"rel"=>"bookmark",
"type"=>"application/xml"
}
],
"status"=>"ACTIVE"
}
}
Are the hostnames significant? Are the port numbers significant? Are the
version IDs significant? Is the next URI component significant? Is the
integer ID significant? Mhhh, maybe it's obvious to the OpenStack
implementers, but it leaves quite some room for error for all the users
out there. We end up having to write a little algorithm that throws away
the hostname and port, then throws away the version number if there is
one -- it really should NOT be part of the URL! -- then looks at the
next path component to decide whether its the resource type and whether
the path component after that is the resource id, or whether there is
further nesting of path components. Then we can assemble a unique ID and
see whether we know about that resource or need to fetch it. It would be
really nice to have a UUID attribute that eliminates this guesswork and
we like UUIDs that start with a type-specific prefix, such as inst-12345
or img-12345.
Our recommendation:
- option 1: use canonical hrefs that can be used as unique IDs, which
means without host/port and without version number
- option 2: use a unique ID with a type prefix and include that as
attribute in hrefs, we like small IDs, but we don't care that much
WRT UUIDs, we try to use integer IDs when we can easily generate them
centrally, but switch to UUIDs when we need to distribute the ID
generation and we keep them as short as practical.
Thanks much!
Thorsten - CTO RightScale
On 6/2/2011 12:40 PM, Jay Pipes wrote:
On Thu, Jun 2, 2011 at 1:18 PM, George Reese<george.re...@enstratus.com> wrote:
I hate UUIDs with a passion.
* They are text fields, which means slower database indexes
Text fields are stored on disk/in memory as bytes the same as any
integer. It's that the number of bytes needed to store it is greater,
resulting in larger indexes and more bytes to store the keys. But, as
Jorge mentioned, some databases have native support for large-integer
types like UUIDs.
* They are completely user-unfriendly. The whole "copy and paste" argument
borders on silliness
Yes, it's not easy to remember UUIDs. That's why virtually every
resource has some other way of identifying themselves. Typically, this
is a name attribute, though not all resources enforce uniqueness on
the name attribute, thus the need for a unique identifier.
I don't see people manually looking up resources based on UUIDs. I see
*machines* manually looking up resources based on UUIDs, and humans
looking up resources by, say, name, or (name, tenant_id) or (name,
user_id), etc.
* And uniqueness across regions for "share nothing" can be managed with a
variety of alternative options without resorting to the ugliness that is UUIDs
Like URIs? I don't know of any other options that would work. Please
let us know what you think about in this respect.
-jay
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