Re: Stopping logical replication protocol

Replication work via Copy API, so for stop replication walcender.c wait
CopyDone. My communication seems like this

FE=> StartReplication(query: START_REPLICATION SLOT
pgjdbc_logical_replication_slot LOGICAL 0/18FCFD0 ("include-xids" 'false',
"skip-empty-xacts" 'true'))
FE=> Query(CopyStart)
<=BE CopyBothResponse
FE=> StandbyStatusUpdate(received: 0/18FCFD0, flushed: 0/0, applied: 0/0,
clock: Tue May 03 22:13:14 MSK 2016)
FE=> CopyData(34)
<=BE CopyData
<=BE CopyData
<=BE Keepalive(lastServerWal: 0/18FCFD0, clock: Tue May 03 22:13:14 MSK
2016 needReply: false)
<=BE XLogData(currWal: 0/0, lastServerWal: 0/0, clock: 0)
<=BE CopyData
<=BE XLogData(currWal: 0/18FD0A0, lastServerWal: 0/18FD0A0, clock: 0)
<=BE CopyData
<=BE XLogData(currWal: 0/18FD1B0, lastServerWal: 0/18FD1B0, clock: 0)
FE=> StopReplication
<=BE CopyData
FE=> CopyDone
<=BE CopyDone
<=BE CopyData
... after few seconds
<=BE CommandStatus(COPY 0)
<=BE ReadyForQuery(I)

The main idea that i want work with same connection without close it.

2016-05-06 19:45 GMT+03:00 Oleksandr Shulgin <oleksandr(dot)shulgin(at)zalando(dot)de>:

> On Fri, May 6, 2016 at 5:23 PM, Vladimir Gordiychuk <folyga(at)gmail(dot)com>
> wrote:
>
>> Hi all,
>>
>> During implementing logical replication protocol for pgjdbc
>> https://github.com/pgjdbc/pgjdbc/pull/550 I faced with strange behavior
>> of the *walcender.c*:
>>
>> 1. When WAL consumer catchup master and change his state to
>> streaming, not available normally complete replication by send CopyDone
>> message until will not generate/create new WAL record. It occurs because
>> logical decoding located in *WalSndWaitForWal* until will not
>> available next WAL record, and it method receive message from consumer even
>> reply on CopyDone with CopyDone but ignore exit from loop and we can wait
>> many times waiting CommandStatus & ReadyForQuery packages on consumer.
>> 2. Logical decoding ignore message from consumer during decoding and
>> writing transaction in socket(*WalSndWriteData*). It affect long
>> transactions with many changes. Because for example if we start decoding
>> transaction that insert 1 million records and after consume 1% of it date
>> we
>> decide stop replication, it will be not available until whole million
>> record will not send to consumer.
>>
>> How exactly are you stopping the replication? If you just stop reading
> you'll likely to hit some problems, but what if you also close the
> connection? I don't think there is any other supported way to do it.
>
> I was working last year on adding support for replication protocol to the
> Python driver: https://github.com/psycopg/psycopg2/pull/322 It would be
> nice if you could skim through this implementation, since it didn't receive
> a whole lot of review.
>
> Cheers.
> --
> Alex
>
>