Re: The documentation for READ COMMITTED may be incomplete or wrong

Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
> On Thu, May 18, 2023 at 04:03:36PM -0400, Tom Lane wrote:
>> What we need to do, I think, is set epqstate->relsubs_done[] for
>> all target relations except the one we are stuffing a tuple into.

> This seems generally reasonable to me.

Here's a draft patch for this. I think it's OK for HEAD, but we are
going to need some different details for the back branches, because
adding a field to struct EPQState would create an ABI break. Our
standard trick of shoving the field to the end in the back branches
won't help, because struct EPQState is actually embedded in
struct ModifyTableState, meaning that all the subsequent fields
therein will move. Maybe we can get away with that, but I bet not.

I think what the back branches will have to do is reinitialize the
relsubs_done array every time through EvalPlanQual(), which is a bit sad
but probably doesn't amount to anything compared to the startup overhead
of the sub-executor.

Debian Code Search doesn't know of any outside code touching
relsubs_done, so I think we are safe in dropping that code in
ExecScanReScan. It seems quite pointless anyway considering
that up to now, EvalPlanQualBegin has always zeroed the whole
array.

regards, tom lane