diff --git a/contrib/adminpack/expected/adminpack.out b/contrib/adminpack/expected/adminpack.out
index 5738b0f6c4..edf3ebfcba 100644
--- a/contrib/adminpack/expected/adminpack.out
+++ b/contrib/adminpack/expected/adminpack.out
@@ -79,7 +79,7 @@ SELECT pg_file_rename('test_file1', 'test_file2');
 (1 row)
 
 SELECT pg_read_file('test_file1');  -- not there
-ERROR:  could not stat file "test_file1": No such file or directory
+ERROR:  could not open file "test_file1" for reading: No such file or directory
 SELECT pg_read_file('test_file2');
  pg_read_file 
 --------------
@@ -108,7 +108,7 @@ SELECT pg_file_rename('test_file2', 'test_file3', 'test_file3_archive');
 (1 row)
 
 SELECT pg_read_file('test_file2');  -- not there
-ERROR:  could not stat file "test_file2": No such file or directory
+ERROR:  could not open file "test_file2" for reading: No such file or directory
 SELECT pg_read_file('test_file3');
  pg_read_file 
 --------------
diff --git a/src/backend/utils/adt/genfile.c b/src/backend/utils/adt/genfile.c
index ceaa6180da..aa49df4d0c 100644
--- a/src/backend/utils/adt/genfile.c
+++ b/src/backend/utils/adt/genfile.c
@@ -106,33 +106,11 @@ read_binary_file(const char *filename, int64 seek_offset, int64 bytes_to_read,
 				 bool missing_ok)
 {
 	bytea	   *buf;
-	size_t		nbytes;
+	size_t		nbytes = 0;
 	FILE	   *file;
 
-	if (bytes_to_read < 0)
-	{
-		if (seek_offset < 0)
-			bytes_to_read = -seek_offset;
-		else
-		{
-			struct stat fst;
-
-			if (stat(filename, &fst) < 0)
-			{
-				if (missing_ok && errno == ENOENT)
-					return NULL;
-				else
-					ereport(ERROR,
-							(errcode_for_file_access(),
-							 errmsg("could not stat file \"%s\": %m", filename)));
-			}
-
-			bytes_to_read = fst.st_size - seek_offset;
-		}
-	}
-
-	/* not sure why anyone thought that int64 length was a good idea */
-	if (bytes_to_read > (MaxAllocSize - VARHDRSZ))
+	/* clamp request size to what we can actually deliver */
+	if (bytes_to_read > (int64) (MaxAllocSize - VARHDRSZ))
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("requested length too large")));
@@ -154,9 +132,56 @@ read_binary_file(const char *filename, int64 seek_offset, int64 bytes_to_read,
 				(errcode_for_file_access(),
 				 errmsg("could not seek in file \"%s\": %m", filename)));
 
-	buf = (bytea *) palloc((Size) bytes_to_read + VARHDRSZ);
+	if (bytes_to_read >= 0)
+	{
+		/* If passed explicit read size just do it */
+		buf = (bytea *) palloc((Size) bytes_to_read + VARHDRSZ);
+
+		nbytes = fread(VARDATA(buf), 1, (size_t) bytes_to_read, file);
+	}
+	else
+	{
+		/* Negative read size, read rest of file */
+		StringInfoData sbuf;
+
+		initStringInfo(&sbuf);
+		/* Leave room in the buffer for the varlena length word */
+		sbuf.len += VARHDRSZ;
+		Assert(sbuf.len < sbuf.maxlen);
 
-	nbytes = fread(VARDATA(buf), 1, (size_t) bytes_to_read, file);
+		while (!(feof(file) || ferror(file)))
+		{
+			size_t		rbytes;
+
+			/* Minimum amount to read at a time */
+#define MIN_READ_SIZE 4096
+
+			/*
+			 * Verify that enlargeStringInfo won't fail; we'd rather give the
+			 * error message for that ourselves.
+			 */
+			if (((Size) MIN_READ_SIZE) >= (MaxAllocSize - (Size) sbuf.len))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("requested length too large")));
+
+			/* OK, ensure that we can read at least MIN_READ_SIZE */
+			enlargeStringInfo(&sbuf, MIN_READ_SIZE);
+
+			/*
+			 * stringinfo.c likes to allocate in powers of 2, so it's likely
+			 * that much more space is available than we asked for.  Use all
+			 * of it, rather than making more fread calls than necessary.
+			 */
+			rbytes = fread(sbuf.data + sbuf.len, 1,
+						   (size_t) (sbuf.maxlen - sbuf.len - 1), file);
+			sbuf.len += rbytes;
+			nbytes += rbytes;
+		}
+
+		/* Now we can commandeer the stringinfo's buffer as the result */
+		buf = (bytea *) sbuf.data;
+	}
 
 	if (ferror(file))
 		ereport(ERROR,