On May 2, 2008, at 2:43 PM, Kevin Grittner wrote:
Alexy Khrabrov wrote:
SInce I don't index on that
new column, I'd assume my old indices would do -- do they change
because of rows deletions/insertions, with the effective new rows
addresses?
Every update is a delete and insert. The new version of the row must
be added to the index. Every access through the index then has to
look at both versions of the row to see which one is "current" for its
transaction. Vacuum will make the space used by the dead rows
available for reuse, as well as removing the old index entries and
making that space available for new index entries.
OK. I've cancelled all previous attempts at UPDATE and will now
create some derived tables. See no changes in the previous huge table
-- the added column was completely empty. Dropped it. Should I
vacuum just in case, or am I guaranteed not to have any extra rows
since no UPDATE actually went through and none are showing?
Cheers,
Alexy
