Re: An issue in JDBC replication API

On Sat, Jun 20, 2020 at 11:32 PM Dave Cramer <davecramer(at)postgres(dot)rocks>
wrote:

>
> 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 ?
>

Sure.

> Dave
>

--
--
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