Speed up COPY into tables with DEFAULT nextval()

Previously the presence of a nextval() prevented the
use of batch-mode COPY.  This patch introduces a
special case just for nextval() functions. In future
we will introduce a general case solution for
labelling volatile functions as safe for use.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index f91f1646dac..7c4039cb7ff 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -2519,9 +2519,20 @@ BeginCopyFrom(Relation rel,
 				defmap[num_defaults] = attnum - 1;
 				num_defaults++;
 
-				/* Check to see if we have any volatile expressions */
+				/*
+				 * If a default expression looks at the table being loaded, then
+				 * it could give the wrong answer when using multi-insert. Since
+				 * database access can be dynamic this is hard to test for
+				 * exactly, so we use the much wider test of whether the
+				 * default expression is volatile. We allow for the special case
+				 * of when the default expression is the nextval() of a sequence
+				 * which in this specific case is known to be safe for use with
+				 * the multi-insert optimisation. Hence we use this special case
+				 * function checker rather than the standard check for
+				 * contain_volatile_functions().
+				 */
 				if (!volatile_defexprs)
-					volatile_defexprs = contain_volatile_functions((Node *) defexpr);
+					volatile_defexprs = contain_volatile_functions_not_nextval((Node *)defexpr);
 			}
 		}
 	}