Fix incorrect comment regarding command completion tags

The comment talked about some Asserts which did not exist and also a
variable name which seems to have long since disappeared.

Rewrite the comment in a way that will hopefully stand the test of
time and inform people why we always write "INSERT 0 <nrows>" instead of
"INSERT <nrows>" in the command completion tag for INSERT.

Reviewed-by: Mark Dilger
Discussion: https://postgr.es/m/CAApHDvpiUg09AvvGAVopNAKemA9z-kCmt7Fi6HKauc32bKzx4w@mail.gmail.com

diff --git a/src/backend/tcop/dest.c b/src/backend/tcop/dest.c
index c952cbea8bd95f966c4cb6a68be90d6a6951519a..6afaa153cad6c97c010661e609111dfd8048c095 100644 (file)
--- a/src/backend/tcop/dest.c
+++ b/src/backend/tcop/dest.c
@@ -178,17 +178,18 @@ EndCommand(const QueryCompletion *qc, CommandDest dest, bool force_undecorated_o
            /*
             * We assume the tagname is plain ASCII and therefore requires no
             * encoding conversion.
-            *
-            * We no longer display LastOid, but to preserve the wire
-            * protocol, we write InvalidOid where the LastOid used to be
-            * written.
-            *
-            * All cases where LastOid was written also write nprocessed
-            * count, so just Assert that rather than having an extra test.
             */
            tag = qc->commandTag;
            tagname = GetCommandTagName(tag);
 
+           /*
+            * In PostgreSQL versions 11 and earlier, it was possible to
+            * create a table WITH OIDS.  When inserting into such a table,
+            * INSERT used to include the Oid of the inserted record in the
+            * completion tag.  To maintain compatibility in the wire
+            * protocol, we now write a "0" (for InvalidOid) in the location
+            * where we once wrote the new record's Oid.
+            */
            if (command_tag_display_rowcount(tag) && !force_undecorated_output)
                snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
                         tag == CMDTAG_INSERT ?