Re: HA Setup Review

On Tue, Apr 30, 2024 at 12:30 PM akshay polji <akshay(dot)polji(at)gmail(dot)com>
wrote:

> ---- Point - 3
> "You can switch from async to sync replication just before patching, and
> then switch back to async when it's completed." --> I am a little confused
> here. What benefit do we get by switching from async to sync replication
> before patching?
>

The *guarantee* that all transactions committed on the primary have been
written to the secondary just before shutting down Primary.

> I mean that would block the transactions on the primary DB right?
>

Wrong 99.99% of the time. It *blocks* the transaction *IFF the network/WAN
link is down*.

When the WAN link is up, you "just" get cascading transaction
*slowness* because
of WAN latency.

Thus... you leave replication to the remote DR site in asynchronous mode
until that very specific point when you need to guarantee remote
consistency: *just before* you shut down the Primary for patching.

Once the Primary is patched, and replication is restored, then you can
change back to async mode.