On 04/26/2014 11:18 AM, Tom Lane wrote: > It's worth noting in this connection that we've never tried hard to ensure > that "database identifiers" are actually unique. One potentially serious > issue is that slave servers will have the same identifier as their master.
Yeah, this is one of those things I've been thinking about. The proble is that we need a "node" ID, which identifies the PostgreSQL instance, and a "dataset ID", which identifies the chain of data, especially when combined with the timeline ID. So a master and replica would have different node IDs, but the same dataset ID, until the replica is promoted, at which point its dataset ID + timeline No. would change. This would allow for relatively easy management of large clusters by allowing automated identification of databases and their mirrors. However, there's a fundamental problem with the concept of the dataset ID in that there's absolutely no way for PostgreSQL to know when it has a unique dataset. Consider a downtime database file cloning for example; the two databases would have the same identifier and yet both be standalones which quickly diverge. So I haven't thought of a good solution to that. We could implement a NodeID, though, based on some combination of IP/MAC address and port though. Not entirely reliable, but better than nothing ... -- Josh Berkus PostgreSQL Experts Inc. http://pgexperts.com -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers