Re: [HACKERS] make async slave to wait for lsn to be replayed

On 2 February 2018 at 18:46, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Feb 2, 2018 at 3:46 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> In PG11, I propose the following command, sticking mostly to Ants'
>> syntax, and allowing to wait for multiple events before it returns. It
>> doesn't hold snapshot and will not get cancelled by Hot Standby.
>>
>> WAIT FOR event [, event ...] options
>>
>> event is
>> LSN value
>> TIMESTAMP value
>>
>> options
>> TIMEOUT delay
>> UNTIL TIMESTAMP timestamp
>> (we have both, so people don't need to do math, they can use whichever
>> they have)
>
> WAIT FOR TIMEOUT sounds a lot like SELECT pg_sleep_for(), and WAIT
> UNTIL TIMESTAMP sounds a lot like SELECT pg_sleep_until().

Yes, it sounds very similar. It's the behavior that differs; I read
and agreed with yours and Thomas' earlier comments on that point.

As pointed out upthread, the key difference is whether it gets
cancelled on Hot Standby and whether you can call it in a non-READ
COMMITTED transaction.

--
Simon Riggs http://www.2ndQuadrant.com/
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