Re: Existence check for suitable index in advance when concurrently refreshing.

On Tue, Jan 26, 2016 at 9:33 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> Hi all,
>
> In concurrently refreshing materialized view, we check whether that
> materialized view has suitable index(unique and not having WHERE
> condition), after filling data to new snapshot
> (refresh_matview_datafill()).
> This logic leads to taking a lot of time until postgres returns ERROR
> log if that table doesn't has suitable index and table is large. it
> wastes time.
> I think we should check whether that materialized view can use
> concurrently refreshing or not in advance.

+1

> The patch is attached.
>
> Please give me feedbacks.

+            indexRel = index_open(indexoid, RowExclusiveLock);

Can we use AccessShareLock here, instead?

+            if (indexStruct->indisunique &&
+                IndexIsValid(indexStruct) &&
+                RelationGetIndexExpressions(indexRel) == NIL &&
+                RelationGetIndexPredicate(indexRel) == NIL)
+                hasUniqueIndex = true;
+
+            index_close(indexRel, RowExclusiveLock);

In the case where hasUniqueIndex = true, ISTM that we can get out of
the loop immediately just after calling index_close(). No?

+    /* Must have at least one unique index */
+    Assert(foundUniqueIndex);

Can we guarantee that there is at least one valid unique index here?
If yes, it's better to write the comment about that.

Regards,

-- 
Fujii Masao