hash join error improvement (old)

[Alvaro Herrera]

I recently noticed this in a customer log file:
  ERROR:  could not read from hash-join temporary file: Success

The problem is we're reporting with %m when the problem is a partial
read or write.

I propose the attached patch to solve it: report "wrote only X of X
bytes".  This caused a lot of other trouble, the cause of which I've
been unable to pinpoint as yet.  But in the meantime, this is already a
small improvement.

-- 
Álvaro Herrera

diff --git a/src/backend/executor/nodeHashjoin.c b/src/backend/executor/nodeHashjoin.c
index d13efc4d98..377554772b 100644
--- a/src/backend/executor/nodeHashjoin.c
+++ b/src/backend/executor/nodeHashjoin.c
@@ -882,16 +882,26 @@ ExecHashJoinSaveTuple(MinimalTuple tuple, uint32 hashvalue,
 	}
 
 	written = BufFileWrite(file, (void *) &hashvalue, sizeof(uint32));
+	if (written < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to hash-join temporary file: %m")));
 	if (written != sizeof(uint32))
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not write to hash-join temporary file: %m")));
+				 errmsg("could not write to hash-join temporary file: wrote only %d of %d bytes",
+						(int) written, (int) sizeof(uint32))));
 
 	written = BufFileWrite(file, (void *) tuple, tuple->t_len);
-	if (written != tuple->t_len)
+	if (written < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not write to hash-join temporary file: %m")));
+	if (written != tuple->t_len)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to hash-join temporary file: wrote only %d of %d bytes",
+						(int) written, (int) tuple->t_len)));
 }
 
 /*
@@ -929,20 +939,30 @@ ExecHashJoinGetSavedTuple(HashJoinState *hjstate,
 		ExecClearTuple(tupleSlot);
 		return NULL;
 	}
-	if (nread != sizeof(header))
+	if (nread < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not read from hash-join temporary file: %m")));
+	if (nread != sizeof(header))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read from hash-join temporary file: read only %d of %d bytes",
+						(int) nread, (int) sizeof(header))));
 	*hashvalue = header[0];
 	tuple = (MinimalTuple) palloc(header[1]);
 	tuple->t_len = header[1];
 	nread = BufFileRead(file,
 						(void *) ((char *) tuple + sizeof(uint32)),
 						header[1] - sizeof(uint32));
-	if (nread != header[1] - sizeof(uint32))
+	if (nread < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not read from hash-join temporary file: %m")));
+	if (nread != header[1] - sizeof(uint32))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read from hash-join temporary file: read only %d of %d bytes",
+						(int) nread, (int) (header[1] - sizeof(uint32)))));
 	return ExecStoreMinimalTuple(tuple, tupleSlot, true);
 }