[PATCH] Better Performance for PostgreSQL with large INSERTs

Sometimes, storing documents (eg. PDFs) in a database
is much easier than using a separate storage (like S3, NFS, etc.).

(Because of issues like backup integrity, availability,
service dependencies, access rights, encryption of data, etc..)

With this patch:

```diff
diff --git i/src/backend/libpq/pqcomm.c w/src/backend/libpq/pqcomm.c
index e517146..936b073 100644
--- i/src/backend/libpq/pqcomm.c
+++ w/src/backend/libpq/pqcomm.c
@@ -117,7 +117,8 @@ static List *sock_paths = NIL;
*/

#define PQ_SEND_BUFFER_SIZE 8192
-#define PQ_RECV_BUFFER_SIZE 8192
+#define PQ_RECV_BUFFER_SIZE 2097152
+

static char *PqSendBuffer;
static int PqSendBufferSize; /* Size send buffer */
```

ie. changing the network receive buffer size from 8KB to 2MB,
got 7% better INSERT performance when storing BLOBs.

The 2MB value is just what we tried, 128kB or 256kB works as well.
The main point is to reduce the number of syscalls for receiving data
to about half of what it is with 8KB.

Thank you for your consideration!

Regards,

Phil