Re: Parallel vacuum workers prevent the oldest xmin from advancing

On 10/6/21, 12:13 AM, "Masahiko Sawada" <sawada(dot)mshk(at)gmail(dot)com> wrote:
> A customer reported that during parallel index vacuum, the oldest xmin
> doesn't advance. Normally, the calculation of oldest xmin
> (ComputeXidHorizons()) ignores xmin/xid of processes having
> PROC_IN_VACUUM flag in MyProc->statusFlags. But since parallel vacuum
> workers don’t set their statusFlags, the xmin of the parallel vacuum
> worker is considered to calculate the oldest xmin. This issue happens
> from PG13 where the parallel vacuum was introduced. I think it's a
> bug.

+1

> To fix it, I thought that we change the create index code and the
> vacuum code so that the individual parallel worker sets its status
> flags according to the leader’s one. But ISTM it’d be better to copy
> the leader’s status flags to workers in ParallelWorkerMain(). I've
> attached a patch for HEAD.

The patch seems reasonable to me.

Nathan