Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold < - Mailing list pgsql-committers

On Fri, Jun 3, 2016 at 4:24 PM, Kevin Grittner <kgrittn@gmail.com> wrote:

> Consequently, causing the index to be ignored in planning when
> using the old index

That last line should have read "using an old snapshot"

> is not a nice optimization, but necessary for
> correctness.  We already have logic to do this for other cases
> (like HOT updates), so it is a matter of tying in to that existing
> code correctly.  This won't be all that novel.

Just to demonstrate that, the minimal patch to fix behavior in this
area would be:

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 31a1438..6c379da 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -2268,6 +2268,9 @@ IndexBuildHeapRangeScan(Relation heapRelation,
        Assert(numblocks == InvalidBlockNumber);
    }
 
+   if (old_snapshot_threshold >= 0)
+       indexInfo->ii_BrokenHotChain = true;
+
    reltuples = 0;
 
    /*