info.md

Follow the link for more info:

http://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=84ac126ee728ede5b6370d60dd2b1c299f49ed2f

postgresql9.6beta2-on-conflict-update-trigger.diff

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index dabaea9..9db4c91 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -1181,8 +1181,17 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,
 	/* Project the new tuple version */
 	ExecProject(resultRelInfo->ri_onConflictSetProj, NULL);
 
+	/*
+	 * Note that it is possible that the target tuple has been modified in
+	 * this session, after the above heap_lock_tuple. We choose to not error
+	 * out in that case, in line with ExecUpdate's treatment of similar
+	 * cases. This can happen if an UPDATE is triggered from within
+	 * ExecQual(), ExecWithCheckOptions() or ExecProject() above, e.g. by
+	 * selecting from a wCTE in the ON CONFLICT's SET.
+	 */
+
 	/* Execute UPDATE with projection */
-	*returning = ExecUpdate(&tuple.t_data->t_ctid, NULL,
+	*returning = ExecUpdate(&tuple.t_self, NULL,
 							mtstate->mt_conflproj, planSlot,
 							&mtstate->mt_epqstate, mtstate->ps.state,
 							canSetTag);

brew edit postgresql

  devel do
    url "https://ftp.postgresql.org/pub/source/v9.5beta2/postgresql-9.5beta2.tar.bz2"
    sha256 "031051cd50ebc4ab07da4e6587c59af6712b21979c486b1af0c31e97e1d9e703"
    version "9.5beta2"
++    patch do
++        url "https://gist.githubusercontent.com/Gurpartap/b213202380f655bd10a1/raw/8901e21b50bfae67c2c026a1060b2d2e28867108/postgresql9.6beta2-on-conflict-update-trigger.diff"
++        sha256 "445093dcb8a36c10d41b7836d4a1190ba8f45020b420bf17fc9f327ec477d82b"
++    end
  end