Re: Connections hang indefinitely while taking a gin index's LWLockbuffer_content lock

On Thu, Mar 21, 2019 at 9:26 PM Simon Riggs <simon@2ndquadrant.com> wrote:

> It's been pointed out to me that 52ac6cd2d0cd70e01291e0ac4ee6d068b69bc478
> introduced a WAL incompatibility that has not been flagged.
>
> In ginRedoDeletePage() we use the struct directly to read the WAL record, so if a WAL record was written prior to 52ac6cd2d0cd70e01291e0ac4ee6d068b69bc478, yet read by code at 52ac6cd2d0cd70e01291e0ac4ee6d068b69bc478 or later then we will have problems, since deleteXid will not be set correctly.
>
> It seems this should not have been backpatched.
>
> Please give your assessment.

Oh, right.  This is my fault.

However, I think this still can be backpatched correctly.  We can
determine whether xlog record data contains deleteXid by its size.
See the attached patch.  I haven't test this yet.  I'm going to test
it.  If OK, then push.