From e3a58c8835a2cd428b8534dd8df30a7cb96c976b Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Fri, 17 Feb 2017 19:32:15 -0500
Subject: [PATCH] Optimize query for information_schema.constraint_column_usage
The way the old query was written prevented some join optimizations
because the join conditions were hidden inside a CASE expression. With
a large number of constraints, the query became unreasonably slow. The
new query performs much better.
From: Alexey Bashtanov <bashtanov@imap.cc>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
---
src/backend/catalog/information_schema.sql | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/backend/catalog/information_schema.sql b/src/backend/catalog/information_schema.sql
index 9a53003ecff..51795cd6ded 100644
--- a/src/backend/catalog/information_schema.sql
+++ b/src/backend/catalog/information_schema.sql
@@ -801,8 +801,8 @@ CREATE VIEW constraint_column_usage AS
WHERE nr.oid = r.relnamespace
AND r.oid = a.attrelid
AND nc.oid = c.connamespace
- AND (CASE WHEN c.contype = 'f' THEN r.oid = c.confrelid AND a.attnum = ANY (c.confkey)
- ELSE r.oid = c.conrelid AND a.attnum = ANY (c.conkey) END)
+ AND r.oid = CASE c.contype WHEN 'f' THEN c.confrelid ELSE c.conrelid END
+ AND a.attnum = ANY (CASE c.contype WHEN 'f' THEN c.confkey ELSE c.conkey END)
AND NOT a.attisdropped
AND c.contype IN ('p', 'u', 'f')
AND r.relkind IN ('r', 'P')
--
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