Re: UUIDs & Clustered Indexes

Tom,

Ah, that makes more sense. Thank you very much!

On Tue, Aug 30, 2016 at 9:15 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Luke Gordon <gordysc(at)gmail(dot)com> writes:
> > However, according to a message on this mailing list, Postgres doesn't
> have
> > clustered indexes:
> > "But Postgres doesn't _have_ clustered indexes, so that article doesn't
> > apply at all. The other authors appear to have missed this important
> point."
> > https://www.postgresql.org/message-id/56798352.7060902%40uchicago.edu
>
> > But, doing a quick check, it appears Postgres does indeed have a
> mechanism
> > for a clustered index:
> > https://www.postgresql.org/docs/9.5/static/sql-cluster.html
>
> CLUSTER just does a one-time sort to put the table into index order.
> There is no mechanism that would cause subsequent insertions of new keys
> to respect that ordering, so it's pretty much irrelevant to the argument
> about whether new UUID keys need to be generated in some ordered fashion.
>
> Do you actually *need* UUID keys, and if so why? A plain old bigint
> column is smaller, cheaper to index, and the natural mechanism for
> generating it (ie a sequence) will tend to preserve ordering for free.
>
> regards, tom lane
>