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35 lines
1.3 KiB
Markdown
35 lines
1.3 KiB
Markdown
# Use Rename To Hot Swap Two Tables
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The [`alter
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table`](https://www.postgresql.org/docs/current/sql-altertable.html) command
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can be used to [rename a
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table](https://www.postgresqltutorial.com/postgresql-tutorial/postgresql-rename-table/).
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Because it is changing the name of a reference rather than actually moving any
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data around, it is very fast.
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We can exploit the speed of a _rename_ to hot swap two tables. This is useful
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for a situation where we've created an identical table with a small fraction of
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the data of the original table. By hot swapping them, we've exchanged the large
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table for a smaller one without our application code noticing anything
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happened.
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Let's assume we have a massive `events` table and then a much smaller
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`new_events` table with the same structure.
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The following transaction will swap those two tables in the blink of an eye.
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```sql
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begin;
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alter table events rename to old_events;
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alter table new_events rename to events;
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commit;
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```
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The resulting `old_events` table can then be deleted at our convenience.
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The other nice thing about this approach is that, before deleting `old_events`,
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you can easily and quickly swap them back using the same approach. It is always
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a comfort when huge changes like this are easy to reverse if necessary.
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