hi,

recently we added a change in Ceilometer to lower the size of our id fields in our storage model[1]. the reason we did this was because the original size of varchar(255) we assigned to ids were so large that if we wanted to generate some of our larger constraint requirements, it would hit index limits of the sql backend.

[disclaimer: i'm not an expert on uuid] typically, a uuid is 36 chars long, according to google, somtimes a bit longer. in Ceilometer, we lowered our size to varchar(128) to get some buffer space, this apparently was too restrictive on the ids we use in OpenStack as our change started breaking things[2].

so for discussion, i'm hoping to get some conditions (standardisation?) on how we generate ids. most people seem to be using uuid4() to generate ids -- this seems to be logical. i think the problem seems to be when we add namespacing prefix. can we set a cap on namespace prefix? say 32char? possibly [<optional 32char prefix>:]uuid4()?

just brainstorming, but my main goal would be to have ids a reasonable size (and hopefully consistent).

[1] https://bugs.launchpad.net/ceilometer/+bug/1353039
[2] https://bugs.launchpad.net/ceilometer/+bug/1468916

cheers,

--
gord


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