Re: Minimal logical decoding on standbys

On 03/13/2019 08:40 PM, tushar wrote:
> Hi ,
>
> I am getting a server crash on standby while executing 
> pg_logical_slot_get_changes function   , please refer this scenario
>
> Master cluster( ./initdb -D master)
> set wal_level='hot_standby in master/postgresql.conf file
> start the server , connect to  psql terminal and create a physical 
> replication slot ( SELECT * from 
> pg_create_physical_replication_slot('p1');)
>
> perform pg_basebackup using --slot 'p1'  (./pg_basebackup -D slave/ -R 
> --slot p1 -v))
> set wal_level='logical' , hot_standby_feedback=on, 
> primary_slot_name='p1' in slave/postgresql.conf file
> start the server , connect to psql terminal and create a logical 
> replication slot (  SELECT * from 
> pg_create_logical_replication_slot('t','test_decoding');)
>
> run pgbench ( ./pgbench -i -s 10 postgres) on master and select 
> pg_logical_slot_get_changes on Slave database
>
> postgres=# select * from pg_logical_slot_get_changes('t',null,null);
> 2019-03-13 20:34:50.274 IST [26817] LOG:  starting logical decoding 
> for slot "t"
> 2019-03-13 20:34:50.274 IST [26817] DETAIL:  Streaming transactions 
> committing after 0/6C000060, reading WAL from 0/6C000028.
> 2019-03-13 20:34:50.274 IST [26817] STATEMENT:  select * from 
> pg_logical_slot_get_changes('t',null,null);
> 2019-03-13 20:34:50.275 IST [26817] LOG:  logical decoding found 
> consistent point at 0/6C000028
> 2019-03-13 20:34:50.275 IST [26817] DETAIL:  There are no running 
> transactions.
> 2019-03-13 20:34:50.275 IST [26817] STATEMENT:  select * from 
> pg_logical_slot_get_changes('t',null,null);
> TRAP: FailedAssertion("!(data == tupledata + tuplelen)", File: 
> "decode.c", Line: 977)
> server closed the connection unexpectedly
>     This probably means the server terminated abnormally
>     before or while processing the request.
> The connection to the server was lost. Attempting reset: 2019-03-13 
> 20:34:50.276 IST [26809] LOG:  server process (PID 26817) was 
> terminated by signal 6: Aborted
>
Andres - Do you think - this is an issue which needs to  be fixed ?

-- 
regards,tushar
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