Hi, On 2021-04-05 21:57:12 +0200, Mats Kindahl wrote: > 2. In the storage layer, the function RelationDropStorage is called, > which will record the table to be dropped in the pendingDeletes > > When committing (or aborting) the transaction, there are two calls that are > interesting, in this order: > > 1. CallXactCallbacks which calls registered callbacks > 2. smgrDoPendingDeletes, which calls the storage layer directly to > perform the actual deletion, if necessary. > > Now, suppose that we want to replace the storage layer with a different > one. It is straightforward to replace it by implementing the Table AM > methods above, but we are missing a callback on dropping the table. If we > have that, we can record the table-to-be-dropped in a similar manner to how > the heap AM does it and register a transaction callback using > RegisterXactCallback.
I don't think implementing dropping relation data at-commit/rollback using xact callbacks can be correct. The dropping needs to be integrated with the commit / abort records, so it is redone during crash recovery - that's not possible with xact callbacks. To me it still seems fundamentally the wrong direction to implement a "drop relation callback" tableam callback. Greetings, Andres Freund
