Re: runtime error copying oids field

On 2020-Nov-30, Zhihong Yu wrote:

> This was the line runtime error was raised:
>
>         memcpy(part_oids, partdesc->oids, sizeof(Oid) * nparts);
>
> From RelationBuildPartitionDesc we can see that:
>
>       if (nparts > 0)
>       {
>               PartitionBoundInfo boundinfo;
>               int                *mapping;
>               int                     next_index = 0;
>
>               result->oids = (Oid *) palloc0(nparts * sizeof(Oid));
>
> The cause was oids field was not assigned due to nparts being 0.
> This is verified by additional logging added just prior to the memcpy call.
>
> I want to get the community's opinion on whether a null check should be
> added prior to the memcpy() call.

As far as I understand, we do want to avoid memcpy's of null pointers;
see [1].

In this case I think it'd be sane to skip the complete block, not just
the memcpy, something like

diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index ca24620fd0..d35deb433a 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -1163,15 +1163,17 @@ DefineIndex(Oid relationId,

        if (partitioned)
        {
+               PartitionDesc partdesc;
+
                /*
                 * Unless caller specified to skip this step (via ONLY), process each
                 * partition to make sure they all contain a corresponding index.
                 *
                 * If we're called internally (no stmt->relation), recurse always.
                 */
-               if (!stmt->relation || stmt->relation->inh)
+               partdesc = RelationGetPartitionDesc(rel);
+               if ((!stmt->relation || stmt->relation->inh) && partdesc->nparts > 0)
                {
-                       PartitionDesc partdesc = RelationGetPartitionDesc(rel);
                        int                     nparts = partdesc->nparts;
                        Oid                *part_oids = palloc(sizeof(Oid) * nparts);
                        bool            invalidate_parent = false;

[1] https://www.postgresql.org/message-id/flat/20200904023648.GB3426768%40rfd.leadboat.com