bufmgr: Support multiple in-progress IOs by using resowner

A future patch will add support for extending relations by multiple blocks at
once. To be concurrency safe, the buffers for those blocks need to be marked
as BM_IO_IN_PROGRESS. Until now we only had infrastructure for recovering from
an IO error for a single buffer. This commit extends that infrastructure to
multiple buffers by using the resource owner infrastructure.

This commit increases the size of the ResourceOwnerData struct, which appears
to have a just about measurable overhead in very extreme workloads. Medium
term we are planning to substantially shrink the size of
ResourceOwnerData. Short term the increase is small enough to not worry about
it for now.

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/20221029025420.eplyow6k7tgu6he3@awork3.anarazel.de
Discussion: https://postgr.es/m/20221029200025.w7bvlgvamjfo6z44@awork3.anarazel.de

src/backend/access/transam/xact.c

@@ -2719,8 +2719,7 @@ AbortTransaction(void)
 	pgstat_report_wait_end();
 	pgstat_progress_end_command();
 
-	/* Clean up buffer I/O and buffer context locks, too */
-	AbortBufferIO();
+	/* Clean up buffer context locks, too */
 	UnlockBuffers();
 
 	/* Reset WAL record construction state */
@@ -5080,7 +5079,6 @@ AbortSubTransaction(void)
 
 	pgstat_report_wait_end();
 	pgstat_progress_end_command();
-	AbortBufferIO();
 	UnlockBuffers();
 
 	/* Reset WAL record construction state */

src/backend/postmaster/autovacuum.c

@@ -526,7 +526,6 @@ AutoVacLauncherMain(int argc, char *argv[])
 		 */
 		LWLockReleaseAll();
 		pgstat_report_wait_end();
-		AbortBufferIO();
 		UnlockBuffers();
 		/* this is probably dead code, but let's be safe: */
 		if (AuxProcessResourceOwner)

src/backend/postmaster/bgwriter.c

@@ -167,7 +167,6 @@ BackgroundWriterMain(void)
 		 */
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
-		AbortBufferIO();
 		UnlockBuffers();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Buffers(false);

src/backend/postmaster/checkpointer.c

@@ -271,7 +271,6 @@ CheckpointerMain(void)
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
 		pgstat_report_wait_end();
-		AbortBufferIO();
 		UnlockBuffers();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Buffers(false);

src/backend/postmaster/walwriter.c

@@ -163,7 +163,6 @@ WalWriterMain(void)
 		LWLockReleaseAll();
 		ConditionVariableCancelSleep();
 		pgstat_report_wait_end();
-		AbortBufferIO();
 		UnlockBuffers();
 		ReleaseAuxProcessResources(false);
 		AtEOXact_Buffers(false);

src/backend/storage/buffer/bufmgr.c

@@ -159,10 +159,6 @@ int			checkpoint_flush_after = DEFAULT_CHECKPOINT_FLUSH_AFTER;
 int			bgwriter_flush_after = DEFAULT_BGWRITER_FLUSH_AFTER;
 int			backend_flush_after = DEFAULT_BACKEND_FLUSH_AFTER;
 
-/* local state for StartBufferIO and related functions */
-static BufferDesc *InProgressBuf = NULL;
-static bool IsForInput;
-
 /* local state for LockBufferForCleanup */
 static BufferDesc *PinCountWaitBuf = NULL;
 
@@ -2705,7 +2701,6 @@ InitBufferPoolAccess(void)
 static void
 AtProcExit_Buffers(int code, Datum arg)
 {
-	AbortBufferIO();
 	UnlockBuffers();
 
 	CheckForBufferLeaks();
@@ -4647,7 +4642,7 @@ StartBufferIO(BufferDesc *buf, bool forInput)
 {
 	uint32		buf_state;
 
-	Assert(!InProgressBuf);
+	ResourceOwnerEnlargeBufferIOs(CurrentResourceOwner);
 
 	for (;;)
 	{
@@ -4671,8 +4666,8 @@ StartBufferIO(BufferDesc *buf, bool forInput)
 	buf_state |= BM_IO_IN_PROGRESS;
 	UnlockBufHdr(buf, buf_state);
 
-	InProgressBuf = buf;
-	IsForInput = forInput;
+	ResourceOwnerRememberBufferIO(CurrentResourceOwner,
+								  BufferDescriptorGetBuffer(buf));
 
 	return true;
 }
@@ -4698,8 +4693,6 @@ TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits)
 {
 	uint32		buf_state;
 
-	Assert(buf == InProgressBuf);
-
 	buf_state = LockBufHdr(buf);
 
 	Assert(buf_state & BM_IO_IN_PROGRESS);
@@ -4711,13 +4704,14 @@ TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits)
 	buf_state |= set_flag_bits;
 	UnlockBufHdr(buf, buf_state);
 
-	InProgressBuf = NULL;
+	ResourceOwnerForgetBufferIO(CurrentResourceOwner,
+								BufferDescriptorGetBuffer(buf));
 
 	ConditionVariableBroadcast(BufferDescriptorGetIOCV(buf));
 }
 
 /*
- * AbortBufferIO: Clean up any active buffer I/O after an error.
+ * AbortBufferIO: Clean up active buffer I/O after an error.
  *
  *	All LWLocks we might have held have been released,
  *	but we haven't yet released buffer pins, so the buffer is still pinned.
@@ -4726,46 +4720,42 @@ TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits)
  *	possible the error condition wasn't related to the I/O.
  */
 void
-AbortBufferIO(void)
+AbortBufferIO(Buffer buf)
 {
-	BufferDesc *buf = InProgressBuf;
+	BufferDesc *buf_hdr = GetBufferDescriptor(buf - 1);
+	uint32		buf_state;
 
-	if (buf)
-	{
-		uint32		buf_state;
+	buf_state = LockBufHdr(buf_hdr);
+	Assert(buf_state & (BM_IO_IN_PROGRESS | BM_TAG_VALID));
 
-		buf_state = LockBufHdr(buf);
-		Assert(buf_state & BM_IO_IN_PROGRESS);
-		if (IsForInput)
-		{
-			Assert(!(buf_state & BM_DIRTY));
+	if (!(buf_state & BM_VALID))
+	{
+		Assert(!(buf_state & BM_DIRTY));
+		UnlockBufHdr(buf_hdr, buf_state);
+	}
+	else
+	{
+		Assert(!(buf_state & BM_DIRTY));
+		UnlockBufHdr(buf_hdr, buf_state);
 
-			/* We'd better not think buffer is valid yet */
-			Assert(!(buf_state & BM_VALID));
-			UnlockBufHdr(buf, buf_state);
-		}
-		else
+		/* Issue notice if this is not the first failure... */
+		if (buf_state & BM_IO_ERROR)
 		{
-			Assert(buf_state & BM_DIRTY);
-			UnlockBufHdr(buf, buf_state);
-			/* Issue notice if this is not the first failure... */
-			if (buf_state & BM_IO_ERROR)
-			{
-				/* Buffer is pinned, so we can read tag without spinlock */
-				char	   *path;
-
-				path = relpathperm(BufTagGetRelFileLocator(&buf->tag),
-								   BufTagGetForkNum(&buf->tag));
-				ereport(WARNING,
-						(errcode(ERRCODE_IO_ERROR),
-						 errmsg("could not write block %u of %s",
-								buf->tag.blockNum, path),
-						 errdetail("Multiple failures --- write error might be permanent.")));
-				pfree(path);
-			}
+			/* Buffer is pinned, so we can read tag without spinlock */
+			char	   *path;
+
+			path = relpathperm(BufTagGetRelFileLocator(&buf_hdr->tag),
+							   BufTagGetForkNum(&buf_hdr->tag));
+			ereport(WARNING,
+					(errcode(ERRCODE_IO_ERROR),
+					 errmsg("could not write block %u of %s",
+							buf_hdr->tag.blockNum, path),
+					 errdetail("Multiple failures --- write error might be permanent.")));
+			pfree(path);
 		}
-		TerminateBufferIO(buf, false, BM_IO_ERROR);
 	}
+
+	TerminateBufferIO(buf_hdr, false, BM_IO_ERROR);
 }
 
 /*

src/backend/utils/resowner/resowner.c

@@ -121,6 +121,7 @@ typedef struct ResourceOwnerData
 
 	/* We have built-in support for remembering: */
 	ResourceArray bufferarr;	/* owned buffers */
+	ResourceArray bufferioarr;	/* in-progress buffer IO */
 	ResourceArray catrefarr;	/* catcache references */
 	ResourceArray catlistrefarr;	/* catcache-list pins */
 	ResourceArray relrefarr;	/* relcache references */
@@ -441,6 +442,7 @@ ResourceOwnerCreate(ResourceOwner parent, const char *name)
 	}
 
 	ResourceArrayInit(&(owner->bufferarr), BufferGetDatum(InvalidBuffer));
+	ResourceArrayInit(&(owner->bufferioarr), BufferGetDatum(InvalidBuffer));
 	ResourceArrayInit(&(owner->catrefarr), PointerGetDatum(NULL));
 	ResourceArrayInit(&(owner->catlistrefarr), PointerGetDatum(NULL));
 	ResourceArrayInit(&(owner->relrefarr), PointerGetDatum(NULL));
@@ -517,6 +519,24 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
 
 	if (phase == RESOURCE_RELEASE_BEFORE_LOCKS)
 	{
+		/*
+		 * Abort failed buffer IO. AbortBufferIO()->TerminateBufferIO() calls
+		 * ResourceOwnerForgetBufferIOs(), so we just have to iterate till
+		 * there are none.
+		 *
+		 * Needs to be before we release buffer pins.
+		 *
+		 * During a commit, there shouldn't be any in-progress IO.
+		 */
+		while (ResourceArrayGetAny(&(owner->bufferioarr), &foundres))
+		{
+			Buffer		res = DatumGetBuffer(foundres);
+
+			if (isCommit)
+				elog(PANIC, "lost track of buffer IO on buffer %u", res);
+			AbortBufferIO(res);
+		}
+
 		/*
 		 * Release buffer pins.  Note that ReleaseBuffer will remove the
 		 * buffer entry from our array, so we just have to iterate till there
@@ -746,6 +766,7 @@ ResourceOwnerDelete(ResourceOwner owner)
 
 	/* And it better not own any resources, either */
 	Assert(owner->bufferarr.nitems == 0);
+	Assert(owner->bufferioarr.nitems == 0);
 	Assert(owner->catrefarr.nitems == 0);
 	Assert(owner->catlistrefarr.nitems == 0);
 	Assert(owner->relrefarr.nitems == 0);
@@ -775,6 +796,7 @@ ResourceOwnerDelete(ResourceOwner owner)
 
 	/* And free the object. */
 	ResourceArrayFree(&(owner->bufferarr));
+	ResourceArrayFree(&(owner->bufferioarr));
 	ResourceArrayFree(&(owner->catrefarr));
 	ResourceArrayFree(&(owner->catlistrefarr));
 	ResourceArrayFree(&(owner->relrefarr));
@@ -976,6 +998,44 @@ ResourceOwnerForgetBuffer(ResourceOwner owner, Buffer buffer)
 			 buffer, owner->name);
 }
 
+
+/*
+ * Make sure there is room for at least one more entry in a ResourceOwner's
+ * buffer array.
+ *
+ * This is separate from actually inserting an entry because if we run out
+ * of memory, it's critical to do so *before* acquiring the resource.
+ */
+void
+ResourceOwnerEnlargeBufferIOs(ResourceOwner owner)
+{
+	/* We used to allow pinning buffers without a resowner, but no more */
+	Assert(owner != NULL);
+	ResourceArrayEnlarge(&(owner->bufferioarr));
+}
+
+/*
+ * Remember that a buffer IO is owned by a ResourceOwner
+ *
+ * Caller must have previously done ResourceOwnerEnlargeBufferIOs()
+ */
+void
+ResourceOwnerRememberBufferIO(ResourceOwner owner, Buffer buffer)
+{
+	ResourceArrayAdd(&(owner->bufferioarr), BufferGetDatum(buffer));
+}
+
+/*
+ * Forget that a buffer IO is owned by a ResourceOwner
+ */
+void
+ResourceOwnerForgetBufferIO(ResourceOwner owner, Buffer buffer)
+{
+	if (!ResourceArrayRemove(&(owner->bufferioarr), BufferGetDatum(buffer)))
+		elog(PANIC, "buffer IO %d is not owned by resource owner %s",
+			 buffer, owner->name);
+}
+
 /*
  * Remember that a Local Lock is owned by a ResourceOwner
  *

src/include/storage/bufmgr.h

@@ -181,7 +181,7 @@ extern bool ConditionalLockBufferForCleanup(Buffer buffer);
 extern bool IsBufferCleanupOK(Buffer buffer);
 extern bool HoldingBufferPinThatDelaysRecovery(void);
 
-extern void AbortBufferIO(void);
+extern void AbortBufferIO(Buffer buffer);
 
 extern bool BgBufferSync(struct WritebackContext *wb_context);
 

src/include/utils/resowner_private.h

@@ -30,6 +30,11 @@ extern void ResourceOwnerEnlargeBuffers(ResourceOwner owner);
 extern void ResourceOwnerRememberBuffer(ResourceOwner owner, Buffer buffer);
 extern void ResourceOwnerForgetBuffer(ResourceOwner owner, Buffer buffer);
 
+/* support for IO-in-progress management */
+extern void ResourceOwnerEnlargeBufferIOs(ResourceOwner owner);
+extern void ResourceOwnerRememberBufferIO(ResourceOwner owner, Buffer buffer);
+extern void ResourceOwnerForgetBufferIO(ResourceOwner owner, Buffer buffer);
+
 /* support for local lock management */
 extern void ResourceOwnerRememberLock(ResourceOwner owner, LOCALLOCK *locallock);
 extern void ResourceOwnerForgetLock(ResourceOwner owner, LOCALLOCK *locallock);