Postgresql - How to safely rename table-CodePudding

In PostgreSQL 13, I am loading data to a Staging table which has the same schema structure as the old table i.e. Target table and once all rows are loaded I am Dropping the old table and renaming Staging to the old table name.

The above works, But my concern is even if the table rename command should not take a lot of time still the worst-case scenario, What if someone tries to query the old table at the same time while it was executing the DROP old table query? my understanding is their application will fail basically some sort of table lock issue.

So how can we avoid that or how can we safely rename/switch the table without such issues?

Thanks!

CodePudding user response：

One way to avoid table lock issues while renaming tables in PostgreSQL is to use the "SWAP" functionality. Instead of dropping the old table and renaming the new table to the old table name, you can use the "ALTER TABLE ... RENAME TO ..., ALTER TABLE ... RENAME TO ..." statement to swap the names of the old table and the new table. This will not lock the table during the rename process and will minimize the risk of any issues occurring for users querying the table.

Another way to avoid table lock issues is to use a "Materialized View" which is a snapshot of a query that is stored on disk. You can create a materialized view of your target table and rename it, this way your users will still be able to query the old table while you are renaming it.

Another way is to use a "Partitioning" technique, where you divide your table into smaller parts, you can rename a partition while the other partition can still be queried.

In any case, it's good practice to inform your users of the table rename operation in advance and schedule it during a maintenance window to minimize disruptions.

CodePudding user response：

You can simply do it like this in a single transaction:

START TRANSACTION;

/* this will block until the last concurrent transaction
   that uses the table is done */
DROP TABLE tab;

ALTER TABLE tab_new RENAME TO tab;

COMMIT;

A concurrent transaction that tries to access the table will have to wait until the transaction is done, whereupon it will use the new table. There should be no errors, and the only disruption can happen if a long running concurrent transaction blocks the DROP TABLE for a long time.