On Sat, Mar 05, 2011 at 12:55:18PM +0100, hubert depesz lubaczewski wrote: > perhaps I misunderstood something from commits, but I assumed that in > 9.1 this operation shouldn't rewrite the table: > > CREATE TABLE test ( x varchar(16) ); > insert into test select i::text from generate_series(1,1000000) i; > alter table test alter column x set data type varchar(32); > > but it does. The patch optimizing that case foundered. We may have it in 9.2. The current code only kicks in when the destination has no typmod. When the source/destination type pair are marked "(binary coercible)" in the output of \dC, the optimization applies. Alternately, it applies when one of the types is a constraint-free domain over the other. The practical use cases are a bit thin at present. The main interesting ones are varchar(N) -> text and conversions between domains and their base types. We did these first because they required a proper subset of the code needed to support the more-common cases. > In commit log I see information about "binary coercible" (which doesn't > mean much to me) - so I assumed varchars() can work this way. The applicable definition of "binary coercible" appears in our CREATE CAST documentation. nm -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
