Calculate # of semaphores correctly with --disable-spinlocks.

The old formula didn't take into account that each WAL sender process needs
a spinlock. We had also already exceeded the fixed number of spinlocks
reserved for misc purposes (10). Bump that to 30.

Backpatch to 9.0, where WAL senders were introduced. If I counted correctly,
9.0 had exactly 10 predefined spinlocks, and 9.1 exceeded that, but bump the
limit in 9.0 too because 10 is uncomfortably close to the edge.

diff --git a/src/backend/storage/lmgr/spin.c b/src/backend/storage/lmgr/spin.c
index d262efa300fd830907dc0a3f2179c6ebd5a65c25..56442ed073e966c9c01316de47dd28d395a6f6a4 100644 (file)
--- a/src/backend/storage/lmgr/spin.c
+++ b/src/backend/storage/lmgr/spin.c
@@ -23,6 +23,7 @@
 #include "postgres.h"
 
 #include "miscadmin.h"
+#include "replication/walsender.h"
 #include "storage/lwlock.h"
 #include "storage/spin.h"
 
@@ -50,14 +51,21 @@ SpinlockSemas(void)
 int
 SpinlockSemas(void)
 {
+       int             nsemas;
+
        /*
         * It would be cleaner to distribute this logic into the affected modules,
         * similar to the way shmem space estimation is handled.
         *
-        * For now, though, we just need a few spinlocks (10 should be plenty)
-        * plus one for each LWLock and one for each buffer header.
+        * For now, though, there are few enough users of spinlocks that we just
+        * keep the knowledge here.
         */
-       return NumLWLocks() + NBuffers + 10;
+       nsemas = NumLWLocks();          /* one for each lwlock */
+       nsemas += NBuffers;                     /* one for each buffer header */
+       nsemas += max_wal_senders;      /* one for each wal sender process */
+       nsemas += 30;                           /* plus a bunch for other small-scale use */
+
+       return nsemas;
 }
 
 /*