Re: Minimal logical decoding on standbys

Hi,

On 10/28/21 11:07 PM, Andres Freund wrote:
> Hi,
>
> On 2021-10-28 16:24:22 -0400, Robert Haas wrote:
>> On Wed, Oct 27, 2021 at 2:56 AM Drouvot, Bertrand <bdrouvot@amazon.com> wrote:
>>> So you have in mind to check for XLogLogicalInfoActive() first, and if true, then open the relation and call
>>> RelationIsAccessibleInLogicalDecoding()?
>> I think 0001 is utterly unacceptable. We cannot add calls to
>> table_open() in low-level functions like this. Suppose for example
>> that _bt_getbuf() calls _bt_log_reuse_page() which with 0001 applied
>> would call get_rel_logical_catalog(). _bt_getbuf() will have acquired
>> a buffer lock on the page. The idea that it's safe to call
>> table_open() while holding a buffer lock cannot be taken seriously.
> Yes - that's pretty clearly a deadlock hazard. It shouldn't too hard to fix, I
> think. Possibly a bit more verbose than nice, but...
>
> Alternatively we could propagate the information whether a relcache entry is
> for a catalog from the table to the index. Then we'd not need to change the
> btree code to pass the table down.

+1 for the idea of propagating to the index. If that sounds good to you 
too, I can try to have a look at it.

Thanks Robert and Andres for the feedbacks you have done on the various 
sub-patches.

I've now in mind to work sub patch by sub patch (starting with 0001 
then) and move to the next one once we agree that the current one is 
"ready".

I think that could help us to get this new feature moving forward more 
"easily", what do you think?

Thanks

Bertrand