Re: prevent immature WAL streaming

On 8/23/21, 3:53 PM, "Alvaro Herrera"  wrote:
> As mentioned in the course of thread [1], we're missing a fix for
> streaming replication to avoid sending records that the primary hasn't
> fully flushed yet.  This patch is a first attempt at fixing that problem
> by retreating the LSN reported as FlushPtr whenever a segment is
> registered, based on the understanding that if no registration exists
> then the LogwrtResult.Flush pointer can be taken at face value; but if a
> registration exists, then we have to stream only till the start LSN of
> that registered entry.

I wonder if we need to move the call to RegisterSegmentBoundary() to
somewhere before WALInsertLockRelease() for this to work as intended.
Right now, boundary registration could take place after the flush
pointer has been advanced, which means GetSafeFlushRecPtr() could
still return an unsafe position.

Nathan