Re: Logical decoding on standby

On Tue, Nov 22, 2016 at 1:49 AM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> On 22 November 2016 at 10:20, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>> I'm currently looking at making detection of replay conflict with a
>> slot work by separating the current catalog_xmin into two effective
>> parts - the catalog_xmin currently needed by any known slots
>> (ProcArray->replication_slot_catalog_xmin, as now), and the oldest
>> actually valid catalog_xmin where we know we haven't removed anything
>> yet.
>
> OK, more detailed plan.
>
> The last checkpoint's oldestXid, and ShmemVariableCache's oldestXid,
> are already held down by ProcArray's catalog_xmin. But that doesn't
> mean we haven't removed newer tuples from specific relations and
> logged that in xl_heap_clean, etc, including catalogs or user
> catalogs, it only means the clog still exists for those XIDs.

Really?

--
Robert Haas
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