Re: Synchronizing slots from primary to standby - Mailing list pgsql-hackers

From Nisha Moond
Subject Re: Synchronizing slots from primary to standby
Date
Msg-id CABdArM6Eb_2dSn1+totFCfk32WNhxn=KC-P8SWwNp_K6n8VHyA@mail.gmail.com
Whole thread Raw
In response to Re: Synchronizing slots from primary to standby  (shveta malik <shveta.malik@gmail.com>)
Responses Re: Synchronizing slots from primary to standby
List pgsql-hackers
Review for v47 patch -

(1)
When we try to create a subscription on standby using a synced slot
that is in 'r' sync_state, the subscription will be created at the
subscriber, and on standby, two actions will take place -
    (i)  As copy_data is true by default, it will switch the failover
state of the synced-slot to 'false'.
    (ii) As we don't allow to use synced-slots, it will start giving
the expected error in the log file -
        ERROR:  cannot use replication slot "logical_slot" for logical decoding
        DETAIL:  This slot is being synced from the primary server.
        HINT:  Specify another replication slot.

The first one seems an issue,  it toggles the failover to false and
then it remains false after that. I think it should be fixed.

(2)
With the patch, the 'CREATE SUBSCRIPTION' command with a 'slot_name'
of an 'active' logical slot fails and errors out -
    ERROR:  could not alter replication slot "logical_slot" on
publisher: ERROR:  replication slot "logical_slot1" is active for PID
xxxx

Without the patch, the create subscription with an 'active' slot_name
succeeds and the log file shows the error "could not start WAL
streaming: ERROR:  replication slot "logical_slot" is active for PID
xxxx".

Given that the specified active slot_name has failover set to false
and the create subscription command also specifies failover=false, the
expected behavior of the "with-patch" case is anticipated to be the
same as that of the "without-patch" scenario.



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