A small tweak to some comments for PartitionKeyData

It was not really that obvious that there's meant to be exactly 1 item
in the partexprs List for each zero-valued partattrs element.  Some
incorrect code using these fields was the cause of CVE-2018-1052, so
it's worthwhile to mention how they should be used in the comments.

Author: David Rowley <david.rowley@2ndquadrant.com>

diff --git a/src/include/utils/partcache.h b/src/include/utils/partcache.h
index 873c60fafd2e41840a4865ef2b3786738f7f8d60..2939032f0a99bedee7e14761e43f64e8d7f6578e 100644 (file)
--- a/src/include/utils/partcache.h
+++ b/src/include/utils/partcache.h
@@ -26,9 +26,9 @@ typedef struct PartitionKeyData
        char            strategy;               /* partitioning strategy */
        int16           partnatts;              /* number of columns in the partition key */
        AttrNumber *partattrs;          /* attribute numbers of columns in the
-                                                                * partition key */
+                                                                * partition key or 0 if it's an expr */
        List       *partexprs;          /* list of expressions in the partitioning
-                                                                * key, or NIL */
+                                                                * key, one for each zero-valued partattrs */
 
        Oid                *partopfamily;       /* OIDs of operator families */
        Oid                *partopcintype;      /* OIDs of opclass declared input data types */