On Thu, Feb 25, 2010 at 8:09 PM, Gokulakannan Somasundaram <gokul...@gmail.com> wrote: > I think, somewhere things have been misunderstood. we only need 8 > bytes more per index entry. I thought Postgres has a 8 byte transaction id, > but it is only 4 bytes, so we only need to save the insertion and deletion > xids. So 8 bytes more per tuple. >
Well in the heap we need 4 bytes: xmin 4 bytes: xmax 4 bytes: cid 6 bytes: ctid 6 bytes: various info bits including natts In indexes we currently get away with a reduced header which has few of the 6 bytes of info bits. However the only reason we can do is because we impose arbitrary limitations that work for indexes but wouldn't be reasonable for tables. Such as a lower maximum number of columns, inability to add new columns or drop columns later, etc. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
