Refactor the fsync queue for wider use.

Previously, md.c and checkpointer.c were tightly integrated so that
fsync calls could be handed off and processed in the background.
Introduce a system of callbacks and file tags, so that other modules
can hand off fsync work in the same way.

For now only md.c uses the new interface, but other users are being
proposed.  Since there may be use cases that are not strictly SMGR
implementations, use a new function table for sync handlers rather
than extending the traditional SMGR one.

Instead of using a bitmapset of segment numbers for each RelFileNode
in the checkpointer's hash table, make the segment number part of the
key.  This requires sending explicit "forget" requests for every
segment individually when relations are dropped, but suits the file
layout schemes of proposed future users better (ie sparse or high
segment numbers).

Author: Shawn Debnath and Thomas Munro
Reviewed-by: Thomas Munro, Andres Freund
Discussion: https://postgr.es/m/CAEepm=2gTANm=e3ARnJT=n0h8hf88wqmaZxk0JYkxw+b21fNrw@mail.gmail.com

5 files changed, 130 insertions, 41 deletions

diff --git a/src/include/postmaster/bgwriter.h b/src/include/postmaster/bgwriter.h
index 53b8f5fe3cb..630366f49ef 100644
--- a/src/include/postmaster/bgwriter.h
+++ b/src/include/postmaster/bgwriter.h
@@ -17,6 +17,8 @@
 
 #include "storage/block.h"
 #include "storage/relfilenode.h"
+#include "storage/smgr.h"
+#include "storage/sync.h"
 
 
 /* GUC options */
@@ -31,9 +33,9 @@ extern void CheckpointerMain(void) pg_attribute_noreturn();
 extern void RequestCheckpoint(int flags);
 extern void CheckpointWriteDelay(int flags, double progress);
 
-extern bool ForwardFsyncRequest(RelFileNode rnode, ForkNumber forknum,
-					BlockNumber segno);
-extern void AbsorbFsyncRequests(void);
+extern bool ForwardSyncRequest(const FileTag *ftag, SyncRequestType type);
+
+extern void AbsorbSyncRequests(void);
 
 extern Size CheckpointerShmemSize(void);
 extern void CheckpointerShmemInit(void);
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index 74c34757fb5..a03b4d14a26 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -54,6 +54,18 @@ extern PGDLLIMPORT bool data_sync_retry;
  */
 extern int	max_safe_fds;
 
+/*
+ * On Windows, we have to interpret EACCES as possibly meaning the same as
+ * ENOENT, because if a file is unlinked-but-not-yet-gone on that platform,
+ * that's what you get.  Ugh.  This code is designed so that we don't
+ * actually believe these cases are okay without further evidence (namely,
+ * a pending fsync request getting canceled ... see ProcessSyncRequests).
+ */
+#ifndef WIN32
+#define FILE_POSSIBLY_DELETED(err)	((err) == ENOENT)
+#else
+#define FILE_POSSIBLY_DELETED(err)	((err) == ENOENT || (err) == EACCES)
+#endif
 
 /*
  * prototypes for functions in fd.c
diff --git a/src/include/storage/md.h b/src/include/storage/md.h
new file mode 100644
index 00000000000..a6758a10dcb
--- /dev/null
+++ b/src/include/storage/md.h
@@ -0,0 +1,51 @@
+/*-------------------------------------------------------------------------
+ *
+ * md.h
+ *	  magnetic disk storage manager public interface declarations.
+ *
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/md.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef MD_H
+#define MD_H
+
+#include "storage/block.h"
+#include "storage/relfilenode.h"
+#include "storage/smgr.h"
+#include "storage/sync.h"
+
+/* md storage manager functionality */
+extern void mdinit(void);
+extern void mdclose(SMgrRelation reln, ForkNumber forknum);
+extern void mdcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
+extern bool mdexists(SMgrRelation reln, ForkNumber forknum);
+extern void mdunlink(RelFileNodeBackend rnode, ForkNumber forknum, bool isRedo);
+extern void mdextend(SMgrRelation reln, ForkNumber forknum,
+		 BlockNumber blocknum, char *buffer, bool skipFsync);
+extern void mdprefetch(SMgrRelation reln, ForkNumber forknum,
+		   BlockNumber blocknum);
+extern void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
+	   char *buffer);
+extern void mdwrite(SMgrRelation reln, ForkNumber forknum,
+		BlockNumber blocknum, char *buffer, bool skipFsync);
+extern void mdwriteback(SMgrRelation reln, ForkNumber forknum,
+			BlockNumber blocknum, BlockNumber nblocks);
+extern BlockNumber mdnblocks(SMgrRelation reln, ForkNumber forknum);
+extern void mdtruncate(SMgrRelation reln, ForkNumber forknum,
+		   BlockNumber nblocks);
+extern void mdimmedsync(SMgrRelation reln, ForkNumber forknum);
+
+extern void ForgetDatabaseSyncRequests(Oid dbid);
+extern void DropRelationFiles(RelFileNode *delrels, int ndelrels, bool isRedo);
+
+/* md sync callbacks */
+extern int mdsyncfiletag(const FileTag *ftag, char *path);
+extern int mdunlinkfiletag(const FileTag *ftag, char *path);
+extern bool mdfiletagmatches(const FileTag *ftag, const FileTag *candidate);
+
+#endif							/* MD_H */
diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index 8e982738789..770193e285e 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -18,7 +18,6 @@
 #include "storage/block.h"
 #include "storage/relfilenode.h"
 
-
 /*
  * smgr.c maintains a table of SMgrRelation objects, which are essentially
  * cached file handles.  An SMgrRelation is created (if not already present)
@@ -106,43 +105,6 @@ extern BlockNumber smgrnblocks(SMgrRelation reln, ForkNumber forknum);
 extern void smgrtruncate(SMgrRelation reln, ForkNumber forknum,
 			 BlockNumber nblocks);
 extern void smgrimmedsync(SMgrRelation reln, ForkNumber forknum);
-extern void smgrpreckpt(void);
-extern void smgrsync(void);
-extern void smgrpostckpt(void);
 extern void AtEOXact_SMgr(void);
 
-
-/* internals: move me elsewhere -- ay 7/94 */
-
-/* in md.c */
-extern void mdinit(void);
-extern void mdclose(SMgrRelation reln, ForkNumber forknum);
-extern void mdcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
-extern bool mdexists(SMgrRelation reln, ForkNumber forknum);
-extern void mdunlink(RelFileNodeBackend rnode, ForkNumber forknum, bool isRedo);
-extern void mdextend(SMgrRelation reln, ForkNumber forknum,
-		 BlockNumber blocknum, char *buffer, bool skipFsync);
-extern void mdprefetch(SMgrRelation reln, ForkNumber forknum,
-		   BlockNumber blocknum);
-extern void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
-	   char *buffer);
-extern void mdwrite(SMgrRelation reln, ForkNumber forknum,
-		BlockNumber blocknum, char *buffer, bool skipFsync);
-extern void mdwriteback(SMgrRelation reln, ForkNumber forknum,
-			BlockNumber blocknum, BlockNumber nblocks);
-extern BlockNumber mdnblocks(SMgrRelation reln, ForkNumber forknum);
-extern void mdtruncate(SMgrRelation reln, ForkNumber forknum,
-		   BlockNumber nblocks);
-extern void mdimmedsync(SMgrRelation reln, ForkNumber forknum);
-extern void mdpreckpt(void);
-extern void mdsync(void);
-extern void mdpostckpt(void);
-
-extern void SetForwardFsyncRequests(void);
-extern void RememberFsyncRequest(RelFileNode rnode, ForkNumber forknum,
-					 BlockNumber segno);
-extern void ForgetRelationFsyncRequests(RelFileNode rnode, ForkNumber forknum);
-extern void ForgetDatabaseFsyncRequests(Oid dbid);
-extern void DropRelationFiles(RelFileNode *delrels, int ndelrels, bool isRedo);
-
 #endif							/* SMGR_H */
diff --git a/src/include/storage/sync.h b/src/include/storage/sync.h
new file mode 100644
index 00000000000..124a49ea984
--- /dev/null
+++ b/src/include/storage/sync.h
@@ -0,0 +1,62 @@
+/*-------------------------------------------------------------------------
+ *
+ * sync.h
+ *	  File synchronization management code.
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/sync.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SYNC_H
+#define SYNC_H
+
+#include "storage/relfilenode.h"
+
+/*
+ * Type of sync request.  These are used to manage the set of pending
+ * requests to call a sync handler's sync or unlink functions at the next
+ * checkpoint.
+ */
+typedef enum SyncRequestType
+{
+	SYNC_REQUEST,				/* schedule a call of sync function */
+	SYNC_UNLINK_REQUEST,		/* schedule a call of unlink function */
+	SYNC_FORGET_REQUEST,		/* forget all calls for a tag */
+	SYNC_FILTER_REQUEST			/* forget all calls satisfying match fn */
+} SyncRequestType;
+
+/*
+ * Which set of functions to use to handle a given request.  See the function
+ * table in sync.c.
+ */
+typedef enum SyncRequestHandler
+{
+	SYNC_HANDLER_MD = 0			/* md smgr */
+} SyncRequestHandler;
+
+/*
+ * A tag identifying a file.  Currently it has the members required for md.c's
+ * usage, but sync.c has no knowledge of the internal structure, and it is
+ * liable to change as required by future handlers.
+ */
+typedef struct FileTag
+{
+	int16		handler;		/* SyncRequstHandler value, saving space */
+	int16		forknum;		/* ForkNumber, saving space */
+	RelFileNode rnode;
+	uint32		segno;
+} FileTag;
+
+extern void InitSync(void);
+extern void SyncPreCheckpoint(void);
+extern void SyncPostCheckpoint(void);
+extern void ProcessSyncRequests(void);
+extern void RememberSyncRequest(const FileTag *ftag, SyncRequestType type);
+extern void EnableSyncRequestForwarding(void);
+extern bool RegisterSyncRequest(const FileTag *ftag, SyncRequestType type,
+					bool retryOnError);
+
+#endif							/* SYNC_H */