From: | Kalit Inani <inanikalit31(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | PITR based recovery failing due to difference in max_connections |
Date: | 2023-08-04 04:47:51 |
Message-ID: | CAKOU5k5RtQ_KXwwsgFdzaMUPMqse0RppimjQFXwUkrzWuBGCyw@mail.gmail.com |
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Lists: | pgsql-general |
Hi all,
During PITR based recovery of a postgres instance, we are getting the
following error -
'2023-06-21 23:52:52.232 PDT [24244] FATAL: hot standby is not possible
because max_connections = 150 is a lower setting than on the master server
(its value was 500)'
Here are the steps we are following -
1.
We took a snapshot of the data disk from a Postgres leader node, let’s
call this as source instance.
2.
Then, we modified the MAX_CONNECTIONS in that source instance to 500.
3.
Due to the modification, the following wal_file entry gets generated -
rmgr: XLOG len (rec/tot): 54/54, tx: 0, lsn: 1/5E0000A0, prev
1/5E000028, desc: PARAMETER_CHANGE max_connections=500
max_worker_processes=8 max_wal_senders=10 max_prepared_xacts=0
max_locks_per_xact=64 wal_level=replica wal_log_hints=off
track_commit_timestamp=off
4.
Next, we did a PITR based recovery in another instance. During the
recovery we have used a config file with MAX_CONNECTIONS as 150.
5.
However, the recovery fails with the following error -
'2023-06-21 23:52:52.232 PDT [24244] FATAL: hot standby is not possible
because max_connections = 150 is a lower setting than on the master server
(its value was 500)'
What are the probable solutions to fix this issue? One of the approaches we
tried was to set ‘hot_standby = off’ in postgresql.conf. By doing this, we
are successfully able to restore the source’s content on the destination
instance. However, is this the correct way to move forward?
We also read the postgres documentation for hot_standby -
https://www.postgresql.org/docs/current/hot-standby.html
It mentions -
“The settings of some parameters determine the size of shared memory for
tracking transaction IDs, locks, and prepared transactions. These shared
memory structures must be no smaller on a standby than on the primary in
order to ensure that the standby does not run out of shared memory during
recovery. For example, if the primary had used a prepared transaction but
the standby had not allocated any shared memory for tracking prepared
transactions, then recovery could not continue until the standby's
configuration is changed.”
Does this mean that turning off hot_standby and then performing a recovery
operation may lead to some unintended consequences? Do we always have to
keep these parameter (‘max_connections’) values greater than equal to that
of the source instance?
Thank you,
Kalit.
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