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 

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 */