Using pg-osc only for backfilling data

[ahilmer]

Hi,

I would be interested in using pg-osc but without using any alter statement. My use case would be to get rid of a bloated table by creating a new table and filling it with (a delta) of the original table.

E.g. like this:

pg-online-schema-change perform \
  --dbname "postgres" \
  --host "localhost" \
  --username "jamesbond" \

Would be adding a "fake" alter statement be a workaround or do you have any other ideas?

  --alter-statement 'ALTER TABLE books ADD COLUMN email IF NOT EXISTS new_email varchar' 

[jfrost]

Did you already review https://github.com/shayonj/pg-osc#backfill-data ? Sounds like that is what you're looking for.

[ahilmer]

Hi @jfrost thanks for your quick reply!

Sorry, I think my question was not correctly formulated.

Actually I want to use the backfill feature (--copy-statement) but without altering my table.

But I have to specify an alter statement.

I would like to just give the table name which should get backfilled without an alter statement.

Would be adding this "fake" statement be enough?

--alter-statement 'ALTER TABLE books ADD COLUMN email IF NOT EXISTS new_email varchar'

[jfrost]

I see what you're asking now. Yes, you can use any valid alter table. Here's a simple example using our sample books table that has an id column that is of type int:

  --alter-statement "ALTER TABLE books ALTER COLUMN id TYPE int"

Since it is already of type int, this is basically a no-op. It might be nice to allow skipping the alter-statement, but then we would need to pass in the tablename. PRs welcome!

[ahilmer]

Great, thanks!