Re: Behaviour of take over the synchronous replication

Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:

> What is happening here is that incase of '*' as priority of both
> are same, system will choose whichever comes in list of
> registered standby's first (list is maintained in structure
> WalSndCtl).  Each standby is registered with WalSndCtl when a new
> WALSender is started in function InitWalSenderSlot().  As 'AAA'
> has been registered first it becomes preferred sync standby even
> if priorities of both are same.  When 'AAA' goes down, it marks
> that Slot entry as free (by setting pid=0 in function
> WalSndKill), now when 'AAA' comes back again, it gets that free
> Slot entry and again becomes preferred sync standby.

So, when a user says they don't care about which standby is in sync
mode, the system can decide (based on internal implementation
details not visible to the user) that any node which comes online
could now become the sync node, and freeze commits on the source
database until that newly added node catches up?  Or does the
existing sync node continue in that role until the new "preferred"
node is caught up?

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company