On 28/02/17 04:27, Kyotaro HORIGUCHI wrote:
> Hello.
> Although replication slot is helpful to avoid unwanted WAL
> deletion, on the other hand it can cause a disastrous situation
> by keeping WAL segments without a limit. Removing the causal
> repslot will save this situation but it is not doable if the
> standby is active. We should do a rather complex and forcible
> steps to relieve the situation especially in an automatic
> manner. (As for me, specifically in an HA cluster.)

I agree that that it should be possible to limit how much WAL slot keeps.

> This patch adds a GUC to put a limit to the number of segments
> that replication slots can keep. Hitting the limit during
> checkpoint shows a warining and the segments older than the limit
> are removed.
>> WARNING:  restart LSN of replication slots is ignored by checkpoint
>> DETAIL:  Some replication slots lose required WAL segnents to continue.

However this is dangerous as logical replication slot does not consider
it error when too old LSN is requested so we'd continue replication,
hiding data loss.

  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services

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