Re: [HACKERS] Receive buffer size for the statistics socket - Mailing list pgsql-hackers

I wrote:
> I propose that it'd be a good idea to try to set the stats socket's
> receive buffer size to be a minimum of, say, 100K on all platforms.
> Code for this would be analogous to what we already have in pqcomm.c
> (circa line 760) for forcing up the send buffer size, but SO_RCVBUF
> not SO_SNDBUF.

I experimented with the attached patch.  Modern platforms such as
recent Linux and macOS seem to have default receive buffer sizes
in the 100K-200K range.  The default is less in older systems, but
even my very oldest dinosaurs will let you set it to at least 256K.
(Don't have Windows to try, though.)

I propose committing this (less the debug logging part) to HEAD
once the beta is out, and then back-patching if it doesn't break
anything and seems to improve matters on frogmouth.

            regards, tom lane

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index d4feed1..d868976 100644
*** a/src/backend/postmaster/pgstat.c
--- b/src/backend/postmaster/pgstat.c
***************
*** 93,98 ****
--- 93,101 ----
  #define PGSTAT_POLL_LOOP_COUNT    (PGSTAT_MAX_WAIT_TIME / PGSTAT_RETRY_DELAY)
  #define PGSTAT_INQ_LOOP_COUNT    (PGSTAT_INQ_INTERVAL / PGSTAT_RETRY_DELAY)

+ /* Minimum receive buffer size for the collector's socket. */
+ #define PGSTAT_MIN_RCVBUF        (100 * 1024)
+

  /* ----------
   * The initial size hints for the hash tables used in the collector.
*************** retry2:
*** 574,579 ****
--- 577,620 ----
          goto startup_failed;
      }

+     /*
+      * Try to ensure that the socket's receive buffer is at least
+      * PGSTAT_MIN_RCVBUF bytes, so that it won't easily overflow and lose
+      * data.  Use of UDP protocol means that we are willing to lose data under
+      * heavy load, but we don't want it to happen just because of ridiculously
+      * small default buffer sizes (such as 8KB on older Windows versions).
+      */
+     {
+         int            old_rcvbuf;
+         int            new_rcvbuf;
+         ACCEPT_TYPE_ARG3 rcvbufsize = sizeof(old_rcvbuf);
+
+         if (getsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
+                        (char *) &old_rcvbuf, &rcvbufsize) < 0)
+         {
+             elog(LOG, "getsockopt(SO_RCVBUF) failed: %m");
+             /* if we can't get existing size, always try to set it */
+             old_rcvbuf = 0;
+         }
+
+         new_rcvbuf = PGSTAT_MIN_RCVBUF;
+         if (old_rcvbuf < new_rcvbuf)
+         {
+             if (setsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
+                            (char *) &new_rcvbuf, sizeof(new_rcvbuf)) < 0)
+                 elog(LOG, "setsockopt(SO_RCVBUF) failed: %m");
+         }
+
+         /* this part is just for debugging, not needed at commit: */
+         rcvbufsize = sizeof(new_rcvbuf);
+         if (getsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
+                        (char *) &new_rcvbuf, &rcvbufsize) < 0)
+             elog(LOG, "getsockopt(SO_RCVBUF) failed: %m");
+         else
+             elog(LOG, "getsockopt(SO_RCVBUF) was %d, now %d",
+                  old_rcvbuf, new_rcvbuf);
+     }
+
      pg_freeaddrinfo_all(hints.ai_family, addrs);

      return;

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