Re: LogwrtResult contended spinlock

Maybe we can do something like this,

diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h
index 78987f3154..f6fa90bad8 100644
--- a/src/include/port/atomics.h
+++ b/src/include/port/atomics.h
@@ -580,7 +580,20 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
static inline uint64
pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)
{
+ /*
+ * When using actual (not simulated) atomics, the target variable for
+ * pg_atomic_compare_exchange_u64 must have suitable alignment, which
+ * is acquired naturally on most platforms, but not on 32-bit ones;
+ * persuade the compiler in that case, but fail if we
+ * cannot.
+ */
+#if MAXIMUM_ALIGNOF >= 8
uint64 currval;
+#elif defined(pg_attribute_aligned) && !defined(PG_HAVE_ATOMIC_U64_SIMULATION)
+ pg_attribute_aligned(8) uint64 currval;
+#else
+#error "Must have pg_attribute aligned or simulated atomics"
+#endif

#ifndef PG_HAVE_ATOMIC_U64_SIMULATION
AssertPointerAlignment(ptr, 8);

--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
"Just treat us the way you want to be treated + some extra allowance
for ignorance." (Michael Brusser)