Re: PostgreSQL Replication Lag – WALs Streaming but Not Being Applied

Hi,

Please see what the below parameters are set to (On Standby).

max_standby_streaming_delay
max_standby_archive_delay

Do you have any activity recorded in pg_stat_activity on the standby ?

On Tue, Aug 18, 2026 at 2:06 PM Gyanuba Gyanuba <gyanubagyanuba(at)gmail(dot)com>
wrote:

> Wait pending
>
> On Tue, Aug 18, 2026, 11:34 PM Simon Musila - Localhost <
> smusila1(at)gmail(dot)com> wrote:
>
>> Hello,
>>
>> I would appreciate some guidance on an issue we are experiencing with
>> PostgreSQL streaming replication.
>>
>> The standby appears to be *receiving/streaming WALs and is up to date
>> with the primary*, but the WAL records are not being applied to the
>> standby, resulting in an increasing replication/replay lag.
>>
>> We have confirmed that:
>>
>> - WALs are being streamed from the primary to the standby.
>> - The WAL receiver appears to be active.
>> - The standby is receiving the WALs, but the replay/apply process is
>> not keeping up.
>> - pg_stat_database_conflicts shows no conflicts.
>> - pg_is_wal_replay_paused() returns false.
>> - recovery_min_apply_delay is 0.
>> - hot_standby_feedback is disabled.
>>
>> [image: Screenshot 2026-08-18 at 20.52.58.png]
>>
>> *My questions are:*
>>
>> 1. What could cause WALs to be successfully streamed to the standby
>> but not applied/replayed?
>> 2. What are the best steps to identify what the WAL replay process is
>> waiting on?
>> 3. Is restarting the replication/standby the only practical solution,
>> or is there a way to safely resume WAL replay without restarting?
>> 4. Are there specific PostgreSQL views, wait events, or system
>> metrics that you would recommend checking to identify the bottleneck?
>>
>> I would appreciate any guidance on troubleshooting this and identifying
>> the underlying cause rather than simply restarting the replication whenever
>> this occurs.
>>
>> *NB: This happens on a daily basis!*
>>
>> Thank you in advance.
>>
>> Regards,
>> Musila
>>
>

--
Regards,
Avinash Vallarapu
HexaCluster Corp.
www.hexacluster.ai