Re: Report replication delay as unknown for down standby nodes

If it has to be an integer maybe -1 would be better than 0 which
theoretically is a valid number. But it's possible these third parties
expect a positive number as well

Nadav Shatz
Tailor Brands | CTO

On Thu, Sep 3, 2026 at 7:21 AM Koshino Taiki <koshino(at)sraoss(dot)co(dot)jp> wrote:

> > I think unknown is clear and better than 0 or last known.
>
> Hi Nadav,
>
> Thank you for your feedback.
> I agree that unknown expresses the actual state
> more clearly than either zero or the last known value.
>
> I would also like to ask the other pgpool-hackers subscribers
> for their opinions on this change.
>
> In particular, could changing replication_delay from a numeric
> value to the string unknown affect any third-party monitoring
> tools?
> For example, Prometheus exporters, Zabbix monitoring templates,
> pgpoolAdmin may parse this column and store it as a numeric metric.
>
> If such tools expect this field to always be numeric,
> reporting zero while the delay cannot be measured might be
> the safer option for compatibility,even though unknown is
> semantically more accurate.
> Does anyone know of tools that collect this column as a numeric value,
> or have a preference between unknown and zero?
>
> Regards,
>
> Taiki Koshino<koshino(at)sraoss(dot)co(dot)jp>
> SRA OSS K.K.
> TEL: 03-5979-2701 FAX: 03-5979-2702
> URL: https://www.sraoss.co.jp/
>
>
> ------------------------------
> *差出人:* Nadav Shatz <nadav(at)tailorbrands(dot)com>
> *送信日時:* 2026年9月2日 15:07
> *宛先:* Koshino Taiki <koshino(at)sraoss(dot)co(dot)jp>
> *CC:* pgpool-hackers(at)lists(dot)postgresql(dot)org <
> pgpool-hackers(at)lists(dot)postgresql(dot)org>
> *件名:* Re: Report replication delay as unknown for down standby nodes
>
> I think unknown is clear and better than 0 or last known.
>
>
> Nadav Shatz
> Tailor Brands | CTO
>
> On Wed, Sep 2, 2026 at 3:15 AM Koshino Taiki <koshino(at)sraoss(dot)co(dot)jp> wrote:
>
> Hi,
>
> I investigated and reproduced the replication delay reporting issue
> reported here:
> https://github.com/pgpool/pgpool2/issues/131
>
> After generating replication delay and detaching the standby,
> SHOW POOL_NODES and pcp_node_info continued to report the last measured
> value:
>
> status | pg_status | replication_delay
> -------+-----------+------------------
> down | up | 72354928
>
> Since the delay cannot be measured while the standby is down, this patch
> reports it as "unknown" in both commands:
>
> status | pg_status | replication_delay
> -------+-----------+------------------
> down | up | unknown
>
> localhost 11003 ... down up standby standby unknown streaming async
>
> The stored value is left unchanged to avoid treating an unmeasured delay
> as zero when the standby is attached again.
>
> I also updated the expected output of the 003.failover regression test,
> and the test passes.
>
> Do you think "unknown" is the appropriate output, or would zero or the
> last measured value be preferable?
>
> The patch is attached.
>
> Regards,
> Taiki Koshino
>
>
> Taiki Koshino<koshino(at)sraoss(dot)co(dot)jp>
> SRA OSS K.K.
> TEL: 03-5979-2701 FAX: 03-5979-2702
> URL: https://www.sraoss.co.jp/
>
>