Re: An issue in JDBC replication API

On Sat, 20 Jun 2020 at 14:23, Abbas Butt <abbas(dot)butt(at)enterprisedb(dot)com>
wrote:

> Hi,
>
> On Sat, Jun 20, 2020 at 7:37 PM Dave Cramer <davecramer(at)postgres(dot)rocks>
> wrote:
>
>>
>> Dave Cramer
>> www.postgres.rocks
>>
>>
>> On Fri, 19 Jun 2020 at 19:37, Dave Cramer <davecramer(at)postgres(dot)rocks>
>> wrote:
>>
>>> Hi Abbas,
>>>
>>> Thanks for this I seem to recall something about this.
>>>
>>> Dave Cramer
>>> www.postgres.rocks
>>>
>>>
>>> On Fri, 19 Jun 2020 at 16:40, Abbas Butt <abbas(dot)butt(at)enterprisedb(dot)com>
>>> wrote:
>>>
>>>> Hi,
>>>> I have found that the JDBC replication API does not handle the keep
>>>> alive messages sent by the server correctly.
>>>> A replication client cannot ignore even a single keep alive message
>>>> from the server and it must respond to it.
>>>> If it does not the server will stop WAL sender with the following error:
>>>> LOG: terminating walsender process due to replication timeout
>>>> LOG: disconnection: session time: 0:02:00.173 user=replicant
>>>> database=edb host=127.0.0.1 port=57900
>>>>
>>>> and this is exactly what is happening when I use JDBC replication API.
>>>> The JDBC driver is ignoring the server's keep alive messages and hence
>>>> the server stops the WAL sender and drops the connection.
>>>>
>>>> Attached please find a sample program that I have mostly copied from
>>>> the documentation available here
>>>>
>>>> https://jdbc.postgresql.org/documentation/head/replication.html#logical-replication
>>>>
>>>> When we run this program and do not do any activity on the database
>>>> server (I have tested with server version 12 and JDBC 42.2.14), after some
>>>> time (wal_sender_timeout/2 seconds to be precise) the server stops
>>>> the WAL sender process and drops the connection.
>>>> To use the program follow these steps:
>>>>
>>>> Issue the following commands to the database server:
>>>> ./createuser --superuser --replication -h 127.0.0.1 -p 7777 -U postgres
>>>> replicant
>>>> select pg_drop_replication_slot('radium');
>>>> CREATE TABLE numbers(a int PRIMARY KEY, b varchar(255));
>>>> GRANT SELECT on numbers to replicant;
>>>> INSERT INTO numbers VALUES(10, 'ten'),(20,'twenty'),(30,'thirty');
>>>> CREATE PUBLICATION barium for TABLE numbers;
>>>>
>>>> To run the program use the following commands:
>>>> mvn clean
>>>> mvn package
>>>> java -cp
>>>> target/Lithium-1.0-SNAPSHOT.jar:/home/abbas/tmp/postgresql-42.2.14.jar
>>>> com.edb.App
>>>>
>>>> If my analysis is correct, can we please have this issue fixed in the
>>>> driver?
>>>>
>>>> Best Regards
>>>>
>>>
>>
>> I'll have a look, but we do attempt to handle it here
>> https://github.com/pgjdbc/pgjdbc/blob/f89e62cdce4895f163dc95353cd31614347624b6/pgjdbc/src/main/java/org/postgresql/core/v3/replication/V3PGReplicationStream.java#L137
>>
>
> I had a look at that part of the code. Assuming that the server needs
> reply only if replyRequired (last byte of the keep alive message) is 1 is
> unfortunately not correct. Server is expecting a reply irrespective of the
> replyRequired value. I have tested with libpq as well and I can confirm
> that the last byte of the keep alive message should simply be ignored by
> the client, and a reply must be sent to each keep alive message.
>
>
>>
>> Dave
>>>>
>>>
>>
>
>
>
Can you try changing that line to see if it fixes it ?
Dave