Side effects of reordering columns in PostgreSQL
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by Summer
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Published on 2010-04-08T16:09:32Z
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postgresql
I sometimes re-order the columns in my Postgres DB. Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns.
My question is: what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did beforehand? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record?
Thanks!
~S
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