On Thu., 21 Jun. 2018, 04:30 Tom Lane, <t...@sss.pgh.pa.us> wrote: > Ashwin Agrawal <aagra...@pivotal.io> writes: > > Okay just bouncing another approach, how about generating UUID for a > > postgres instance during initdb and pg_basebackup ? > > There's no uuid generation code in core postgres, for excellent reasons > (lack of portability and lack of failure modes are the main objections). > This is not different in any meaningful way from the proposal to use > timestamps, except for being more complicated.
A v4 UUID is just 128 random bits and some simple formatting. So I really don't understand your concerns about UUID generation. That said, it can already be handled with tablespace maps in pg_basebackup. And any new scheme would need to happen in pg_basebackup too, because it must happen before the tablespace are copied and thr replica is first started. I don't see a big concern with some pg_basebackup --gen-unique-tablespaces option or the like. UUID would be better than timestamp due to the skew issues discussed upthread. But personally I'd just take a label argument. pg_basebackup --tablespace-prefix or the like. For non pg_basebackup uses you have to solve it yourself anyway. Pg doesn't know if it's just been started as a copy, after all, and it's too late to move tablespace then even if we'd do such a thing.
