On Tue, Jul 03, 2007 at 11:36:03AM -0400, Tom Lane wrote: > I'm not sure it's feasible to expect that we can change representations > of user-defined types, either. I don't see how you would do that > without catalog access (to look up the UDT), and the page conversion > procedure is going to have to be able to operate without catalog > accesses. (Thought experiment: a page is read in during crash recovery > or PITR slave operation, and discovered to have the old format.)
Well, there are two types of conversions: 1. Simple byte rearrangement. If it's not too many you could simply build them into pg_migrator. Doesn't help with user-defined types, but maybe you allow plugins to define a seperate hook whose only purpose is to upgrade the value (without catalog access...). 2. Otherwise you could do a VACUUM over the table to touch every page, thus solving it. Dunno what to do about crashing at this point. Hmm, actually, what's the problem with PITR restoring a page in the old format. As long as it's clear it's the old format it'll get fixed when the page is actually used. > BTW, I thought of a likely upgrade problem that we haven't discussed > (AFAIR) in any of the many threads on this subject. What about an index > access method change that involves an index-wide restructuring, such > that it can't be done one page at a time? A plausible example is > changing hash indexes to have multiple buckets per page. Presumably > you can fix the index with REINDEX, but that doesn't meet the goal of > limited downtime, if the index is big. Is there another way? Well, we have concurrent index builds these days. I certainly don't have ideas on how to fix this, especially if the index is on a datatype that has changed format... I suppose those indexes will just have to be rebuilt (a REINDEX will upgrade every page in the table anyway...). I think it'd still be cheaper than dump/restore. Have a nice day, -- Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ > From each according to his ability. To each according to his ability to > litigate.
Description: Digital signature