Re: 回复：how to create index concurrently on partitioned table

On Fri, Sep 11, 2020 at 07:13:01PM -0500, Justin Pryzby wrote:
> On Tue, Sep 08, 2020 at 01:31:05PM +0900, Michael Paquier wrote:
>> - CIC on partitioned relations. (Should we also care about DROP INDEX
>> CONCURRENTLY as well?)
>
> Do you have any idea what you think that should look like for DROP INDEX
> CONCURRENTLY ?

Making the maintenance of the partition tree consistent to the user is
the critical part here, so my guess on this matter is:
1) Remove each index from the partition tree and mark the indexes as
invalid in the same transaction. This makes sure that after commit no
indexes would get used for scans, and the partition dependency tree
pis completely removed with the parent table. That's close to what we
do in index_concurrently_swap() except that we just want to remove the
dependencies with the partitions, and not just swap them of course.
2) Switch each index to INDEX_DROP_SET_DEAD, one per transaction
should be fine as that prevents inserts.
3) Finish the index drop.

Step 2) and 3) could be completely done for each index as part of
index_drop(). The tricky part is to integrate 1) cleanly within the
existing dependency machinery while still knowing about the list of
partitions that can be removed. I think that this part is not that
straight-forward, but perhaps we could just make this logic part of
RemoveRelations() when listing all the objects to remove.
--
Michael