Re: Synchronous Log Shipping Replication

"Fujii Masao" <masao(dot)fujii(at)gmail(dot)com> wrote:

> 3) Patch of introducing new background process which I've called
> WALSender. It takes charge of sending WAL to the slave.
>
> Now, I assume that WALSender also listens the connection from
> the slave, i.e. only one sender process manages multiple slaves.

> The relation between WALSender and backend is 1:1. So,
> the communication mechanism between them can be simple.

I assume that he says only one backend communicates with WAL sender
at a time. The communication is done during WALWriteLock is held,
so other backends wait for the communicating backend on WALWriteLock.
WAL sender only needs to send one signal for each time it sends WAL
buffers to slave.

We could be split the LWLock to WALWriterLock and WALSenderLock,
but the essential point is same.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center