Re: Logical replication 'invalid memory alloc request size 1585837200' after upgrading to 17.5

On Wed, May 21, 2025 at 4:12 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, May 21, 2025 at 11:18 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Mon, May 19, 2025 at 8:08 PM Duncan Sands
> > <duncan.sands@deepbluecap.com> wrote:
> > >
> > > While it is long, it doesn't seem to merit allocating anything like 1GB of
> > > memory.  So I'm guessing that postgres is miscalculating the required size somehow.
> > >
> >
> > We fixed a bug in commit 4909b38af0 to distribute invalidation at the
> > transaction end to avoid data loss in certain cases, which could cause
> > such a problem. I am wondering that even prior to that commit, we
> > would eventually end up allocating the required memory for a
> > transaction for all the invalidations because of repalloc in
> > ReorderBufferAddInvalidations, so why it matter with this commit? One
> > possibility is that we need allocations for multiple in-progress
> > transactions now.
> >
>
> I think the problem here is that when we are distributing
> invalidations to a concurrent transaction, in addition to queuing the
> invalidations as a change, we also copy the distributed invalidations
> along with the original transaction's invalidations via repalloc in
> ReorderBufferAddInvalidations. So, when there are many in-progress
> transactions, each would try to copy all its accumulated invalidations
> to the remaining in-progress transactions. This could lead to such an
> increase in allocation request size.

I agree with this analysis.

> However, after queuing the
> change, we don't need to copy it along with the original transaction's
> invalidations. This is because the copy is only required when we don't
> process any changes in cases like ReorderBufferForget().

It seems that we use the accumulated invalidation message also after
replaying or concurrently aborting a transaction via
ReorderBufferExecuteInvalidations(). Do we need to consider such cases
too?

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com