PosgtgreSQL hot standby reading WAL from muli-attached volume?

From: Gunther Schadow <raj(at)gusw(dot)net>
To: pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: PosgtgreSQL hot standby reading WAL from muli-attached volume?
Date: 2021-04-05 22:22:26
Message-ID: f729e241-3a2e-893c-4108-0041510ca68a@gusw.net
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Hi,

I wonder can we set up a hot standby in such a way that we don't need
any log streaming nor shipping, where instead every hot standby just
mounts the same disk in read-only mode which the master uses to write
his WAL files?

Even without a clustered file system, e.g., a UFS on FreeBSD, one can
have the master mount in read-write mode while all the hot standbys
would mount the volume read-only. Given that WAL logs are written out at
a certain rate, one can at regular intervals issue

mount -u /pg_wal

and it should refresh the metadata, I assume. I am re-reading about
hot-standby, and it strikes me that this method is essentially the "log
shipping" method only that there is no actual "shipping" involved, the
new log files simply appear all of a sudden on the disk.

I suppose there is a question how we know when a new WAL file is
finished appearing? And as I read the log-shipping method may not be
suitable for hot standby use?

Is this something that has been written about already?

regards,
-Gunther

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