"Florian G. Pflug" <[EMAIL PROTECTED]> writes: >> Anyway, if you believe that DDL is infrequent, why are you resistant >> to the idea of WAL-logging cache flushes?
> First, cache invalidations are not the only problem caused by replaying > system-table updates. The whole SnapshotNow > business doesn't exactly make things easier too. So it feels like a > lot of added complexity and code for little gain - unless a *lot* > more things (like locking requests) are logged too. The mention of locking requests brought to mind the following gedankenexperiment: 1. slave server backend is running some long-running query on table X. 2. WAL-reading process receives and executes DROP TABLE X. (It doesn't even have to be a DROP; most varieties of ALTER are enough to create problems for a concurrently-running query.) It's really hard to see how to defend against that without a fairly complete simulation of locking on the slave side. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq