Re: Nicer error when connecting to standby with hot_standby=off

On 2020/04/03 22:49, James Coleman wrote:
> On Thu, Apr 2, 2020 at 5:53 PM David Zhang <david(dot)zhang(at)highgo(dot)ca> wrote:
>>
>> The following review has been posted through the commitfest application:
>> make installcheck-world: not tested
>> Implements feature: tested, passed
>> Spec compliant: not tested
>> Documentation: not tested
>>
>> I applied the patch to the latest master branch and run a test below. The error messages have been separated. Below is the test steps.
>>
>> ### setup primary server
>> initdb -D /tmp/primary/data
>> mkdir /tmp/archive_dir
>> echo "archive_mode='on'" >> /tmp/primary/data/postgresql.conf
>> echo "archive_command='cp %p /tmp/archive_dir/%f'" >> /tmp/primary/data/postgresql.conf
>> pg_ctl -D /tmp/primary/data -l /tmp/primary-logs start
>>
>> ### setup host standby server
>> pg_basebackup -p 5432 -w -R -D /tmp/hotstandby
>> echo "primary_conninfo='host=127.0.0.1 port=5432 user=pgdev'" >> /tmp/hotstandby/postgresql.conf
>> echo "restore_command='cp /tmp/archive_dir/%f %p'" >> /tmp/hotstandby/postgresql.conf
>> echo "hot_standby = off" >> /tmp/hotstandby/postgresql.conf
>> pg_ctl -D /tmp/hotstandby -l /tmp/hotstandby-logs -o "-p 5433" start
>>
>> ### keep trying to connect to hot standby server in order to get the error messages in different stages.
>> while true; do echo "`date`"; psql postgres -p 5433 -c "SELECT txid_current_snapshot();" sleep 0.2; done
>>
>> ### before the patch
>> psql: error: could not connect to server: FATAL: the database system is starting up
>> ...
>>
>> ### after the patch, got different messages, one message indicates hot_standby is off
>> psql: error: could not connect to server: FATAL: the database system is starting up
>> ...
>> psql: error: could not connect to server: FATAL: the database system is up, but hot_standby is off
>> ...
>
> Thanks for the review and testing!

Thanks for the patch! Here is the comment from me.

+ else if (!FatalError && pmState == PM_RECOVERY)
+ return CAC_STANDBY; /* connection disallowed on non-hot standby */

Even if hot_standby is enabled, pmState seems to indicate PM_RECOVERY
until recovery has reached a consistent state. No? So, if my understanding
is right, "FATAL: the database system is up, but hot_standby is off" can
be logged even when hot_standby is on. Which sounds very confusing.

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION