Subject: Re: Minimal logical decoding on standbys
From: tushar <tushar.ahuja@enterprisedb.com>
To: Andres Freund <andres@anarazel.de>
Cc: Petr Jelinek <petr.jelinek@2ndquadrant.com>,
 Robert Haas <robertmhaas@gmail.com>, Craig Ringer <craig@2ndquadrant.com>,
 Petr Jelinek <petr@2ndquadrant.com>, pgsql-hackers@postgresql.org
References: <20181212204154.nsxf3gzqv3gesl32@alap3.anarazel.de>
 <7e905539-7fdc-6b29-5a56-ba48d180fef8@2ndquadrant.com>
 <cbda32d2-eeb6-31b9-a88a-566330a46fc4@enterprisedb.com>
 <20190301174628.rjzoi7arvci5ldcm@alap3.anarazel.de>
 <aeb9759c-ef7b-6a3b-13ad-0709e52726d5@enterprisedb.com>
 <20190304172739.hdkwmtngwx5444un@alap3.anarazel.de>
 <9fce660d-47fc-4294-3084-3769e543da8a@enterprisedb.com>
 <53656d0c-1868-86e8-54a6-216ce74b353a@enterprisedb.com>
Message-ID: <8af22fc0-d08c-f3fa-e7ec-dfb153b3d7b4@enterprisedb.com>
Date: Wed, 10 Apr 2019 12:11:21 +0530
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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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