On Fri, Aug 14, 2009 at 12:37:14PM +0000, Scara Maccai wrote: > I'm asking because since the page layout includes a null bitmap that > "If it is present it begins just after the fixed header and occupies > enough bytes to have one bit per data column", I guess that when all > the bits in the bitmap are used when I add a column (even a nullable > one) the table gets rewritten (to add a new byte to the nullable > bitmap); is this true?
Sort of; there is indeed a null bitmap saying which columns are null. But there's also a number saying how many columns there are and hence each row knows if a new column is going to be off the end and means it doesn't need to rewrite the table when adding a new NULLable column. I made a suggestion about how to generalize this to non-NULLable columns with a default value, but haven't written any code to make it do this yet. -- Sam http://samason.me.uk/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
