Re: more autovacuum fixes

Alvaro Herrera wrote:

> One problem with the patch is this (new code):
>
>     bn = (Backend *) malloc(sizeof(Backend));
> !   if (bn)
>     {
> !       bn->pid = StartAutoVacWorker();
> !       bn->is_autovacuum = true;
> !       /* we don't need a cancel key */
>
> !       if (bn->pid > 0)
> !       {
> !           /* FIXME -- unchecked memory allocation here */
> !           DLAddHead(BackendList, DLNewElem(bn));
>
>
> If the palloc() inside DLNewElem fails, we will fail to report a "fork
> failure" to the launcher.  I am not sure how serious this is.  One idea
> that came to mind was using a PG_TRY block, sending the signal in the
> CATCH block, and then rethrowing the exception.  Is this acceptable?

I noticed another problem: the worker may fail during BaseInit() or
InitProcess().  This is not where most problems will be (that would be
later, in InitPostgres(), which is when the worker connects to a DB) but
still could cause a starvation problem, I think.  Maybe the PG_TRY block
is called for in there, as well as the postmaster code.

--
Alvaro Herrera                               http://www.PlanetPostgreSQL.org/
"The ability to monopolize a planet is insignificant
next to the power of the source"