On 2014-02-03 11:22:45 -0500, Tom Lane wrote:
> Andres Freund <and...@2ndquadrant.com> writes:
> > On larger, multi-socket, machines, startup takes a fair bit of time. As
> > I was profiling anyway I looked into it and noticed that just about all
> > of it is spent in LWLockAssign() called by InitBufferPool(). Starting
> > with shared_buffers=48GB on the server Nate Boley provided, takes about
> > 12 seconds. Nearly all of it spent taking the ShmemLock spinlock.
> > Simply modifying LWLockAssign() to not take the spinlock when
> > !IsUnderPostmaster speeds it up to 2 seconds. While certainly not making
> > LWLockAssign() prettier it seems enough of a speedup to be worthwile
> > nonetheless.
>
> Hm. This patch only works if the postmaster itself never assigns any
> LWLocks except during startup. That's *probably* all right, but it
> seems a bit scary. Is there any cheap way to make the logic actually
> be what your comment claims, namely "Interlocking is not necessary during
> postmaster startup"? I guess we could invent a ShmemInitInProgress global
> flag ...
So, here's a flag implementing things with that flag. I kept your name,
as it's more in line with ipci.c's naming, but it looks kinda odd
besides proc_exit_inprogress.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index c392d4f..ece9674 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -48,6 +48,11 @@ shmem_startup_hook_type shmem_startup_hook = NULL;
static Size total_addin_request = 0;
static bool addin_request_allowed = true;
+/*
+ * Signals whether shared memory is currently being initialized, while the
+ * postmaster hasn't forked any children yet.
+ */
+bool ShmemInitInProgress = false;
/*
* RequestAddinShmemSpace
@@ -97,6 +102,12 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
int numSemas;
/*
+ * We're now initializing shared memory, and we won't have forked
+ * children yet.
+ */
+ ShmemInitInProgress = true;
+
+ /*
* Size of the Postgres shared-memory block is estimated via
* moderately-accurate estimates for the big hogs, plus 100K for the
* stuff that's too small to bother with estimating.
@@ -261,4 +272,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
*/
if (shmem_startup_hook)
shmem_startup_hook();
+
+ if(!IsUnderPostmaster)
+ ShmemInitInProgress = false;
}
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 82ef440..0365f9b 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -355,9 +355,11 @@ CreateLWLocks(void)
* LWLockAssign - assign a dynamically-allocated LWLock number
*
* We interlock this using the same spinlock that is used to protect
- * ShmemAlloc(). Interlocking is not really necessary during postmaster
- * startup, but it is needed if any user-defined code tries to allocate
- * LWLocks after startup.
+ * ShmemAlloc(). Interlocking is not necessary while we're initializing
+ * shared memory, but it is needed for any code allocating LWLocks after
+ * startup. Since we allocate large amounts of LWLocks for the buffer pool
+ * during startup, we avoid taking the spinlock when not needed, as it has
+ * shown to slowdown startup considerably.
*/
LWLock *
LWLockAssign(void)
@@ -368,14 +370,17 @@ LWLockAssign(void)
volatile int *LWLockCounter;
LWLockCounter = (int *) ((char *) MainLWLockArray - 3 * sizeof(int));
- SpinLockAcquire(ShmemLock);
+ if (!ShmemInitInProgress)
+ SpinLockAcquire(ShmemLock);
if (LWLockCounter[0] >= LWLockCounter[1])
{
- SpinLockRelease(ShmemLock);
+ if (!ShmemInitInProgress)
+ SpinLockRelease(ShmemLock);
elog(ERROR, "no more LWLocks available");
}
result = &MainLWLockArray[LWLockCounter[0]++].lock;
- SpinLockRelease(ShmemLock);
+ if (!ShmemInitInProgress)
+ SpinLockRelease(ShmemLock);
return result;
}
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 37eca7a..0f1e00a 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -63,6 +63,7 @@ typedef void (*shmem_startup_hook_type) (void);
/* ipc.c */
extern bool proc_exit_inprogress;
+extern bool ShmemInitInProgress;
extern void proc_exit(int code) __attribute__((noreturn));
extern void shmem_exit(int code);
--
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