Re: walprotocol.h vs frontends

On Mon, Aug 15, 2011 at 5:15 PM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> On Mon, Aug 15, 2011 at 18:12, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>>> Perhaps we should change the protocol so that it explicitly says which
>>> file the streamed piece of WAL belongs to. That way a client could write
>>> it to the correct file without knowing about all those macros.
>>
>> Yeah, maybe.  Otherwise, all that logic is not only implicitly part of
>> the protocol, but essentially impossible to change because it'll be
>> hard-coded into clients.  I wasn't too worried about this before because
>> I supposed that only walsender and walreceiver really needed to know
>
> Wouldn't doing that cause significant overhead? Every single packet
> would have to contain the filename, since the wal stream isn't
> depending onthe filenames in where it cuts off. Also, the way it is
> now a single packet on the replication stream can span multiple WAL
> files... (This is the bug in my previous version that I've been able
> to fix now)

Why not have a specific protocol message to indicate a change of filename?

I don't mean a WAL message, I mean a streaming protocol message.

At present the WALSender only sends from one file at a time, so
sending a message when we open a new file would be straightforward.

Magnus needs some things to make this work for 9.0/9.1, but we don't
need to change 9.2 to allow that, we just need to copy the definitions
for those now-fixed releases.

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