Re: Avoiding Tablespace path collision for primary and standby

On June 20, 2018 10:31:05 AM PDT, Ashwin Agrawal <aagrawal(at)pivotal(dot)io> wrote:
>On Wed, Jun 20, 2018 at 9:39 AM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
>> On Fri, May 25, 2018 at 02:17:23PM -0700, Ashwin Agrawal wrote:
>> >
>> > On Fri, May 25, 2018 at 7:33 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
>wrote:
>> >
>> > Ashwin Agrawal <aagrawal(at)pivotal(dot)io> writes:
>> > > Proposing to create directory with timestamp at time of
>creating
>> > tablespace
>> > > and create symbolic link to it instead.
>> >
>> > I'm skeptical that this solves your problem. What happens when
>the
>> CREATE
>> > TABLESPACE command is replicated to the standby with sub-second
>> delay?
>> >
>> >
>> > I thought timestamps have micro-second precision. Are we expecting
>> tabelspace
>> > to be created, wal logged, streamed, and replayed on mirror in
>> micro-second ?
>>
>> I didn't see anyone answer your question above. We don't expect
>> micro-second replay, but clock skew, which Tom Lane mention, could
>make
>> it appear to be a micro-second replay.
>>
>
>Thanks Bruce for answering. Though I still don't see why clock skew is
>a
>problem here. As I think clock skew only happens across machines. On
>same
>machine why would it be an issue. Problem is only with same machine,
>different machines anyways paths don't collide so even if clock skew
>happens is not a problem. (I understand there may be reservations for
>putting timestamp in directory path, but clock skew argument is not
>clear.)

Clock skew happens within machines too. Both because of multi socket systems and virtualization systems. Also clock adjustments.

Andres
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