Re:A Year with MongoDB
by scubaguy on Friday April 13, 2012 @05:32PM
(#3838952)
For a large table, adding a new column can be non-trivial, each record is updated when the new column is added.
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If you choose to update all of the old records.
As other posts have already mentioned, adding a new column to a table in postgres does so instantly unless you set a default (telling postgres that you want it to update all the old records too).
If you add the default separately from adding the column, you get the default but don't rewrite all the old rows (which remain NULL).