From f84c8601d604811a530dadb53ddb52f08639e72b Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 23 May 2015 16:24:31 -0400
Subject: [PATCH] Add error check for lossy distance functions in index-only
scans.
Maybe we should actually support this, but for the moment let's just
throw an error if the opclass tries it.
---
src/backend/executor/nodeIndexonlyscan.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index 61bd644ab71..976c77b76c6 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -165,6 +165,19 @@ IndexOnlyNext(IndexOnlyScanState *node)
}
}
+ /*
+ * We don't currently support rechecking ORDER BY distances. (In
+ * principle, if the index can support retrieval of the originally
+ * indexed value, it should be able to produce an exact distance
+ * calculation too. So it's not clear that adding code here for
+ * recheck/re-sort would be worth the trouble. But we should at least
+ * throw an error if someone tries it.)
+ */
+ if (scandesc->numberOfOrderBys > 0 && scandesc->xs_recheckorderby)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("lossy distance functions are not supported in index-only scans")));
+
/*
* Predicate locks for index-only scans must be acquired at the page
* level when the heap is not accessed, since tuple-level predicate
--
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