Re: Avoiding Tablespace path collision for primary and standby

On June 20, 2018 10:31:05 AM PDT, Ashwin Agrawal <aagrawal@pivotal.io> wrote:
>On Wed, Jun 20, 2018 at 9:39 AM Bruce Momjian <bruce@momjian.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@sss.pgh.pa.us>
>wrote:
>> >
>> >     Ashwin Agrawal <aagrawal@pivotal.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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