Support PrefetchBuffer() in recovery.

Provide PrefetchSharedBuffer(), a variant that takes SMgrRelation, for
use in recovery.  Rename LocalPrefetchBuffer() to PrefetchLocalBuffer()
for consistency.

Add a return value to all of these.  In recovery, tolerate and report
missing files, so we can handle relations unlinked before crash recovery
began.  Also report cache hits and misses, so that callers can do faster
buffer lookups and better I/O accounting.

Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com

4 files changed, 19 insertions, 6 deletions

diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index bf3b8ad340e..e57f84ee9c8 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -327,8 +327,9 @@ extern int	BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id);
 extern void BufTableDelete(BufferTag *tagPtr, uint32 hashcode);
 
 /* localbuf.c */
-extern void LocalPrefetchBuffer(SMgrRelation smgr, ForkNumber forkNum,
-								BlockNumber blockNum);
+extern PrefetchBufferResult PrefetchLocalBuffer(SMgrRelation smgr,
+												ForkNumber forkNum,
+												BlockNumber blockNum);
 extern BufferDesc *LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum,
 									BlockNumber blockNum, bool *foundPtr);
 extern void MarkLocalBufferDirty(Buffer buffer);
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index bf3b12a2de3..ee91b8fa26c 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -46,6 +46,15 @@ typedef enum
 								 * replay; otherwise same as RBM_NORMAL */
 } ReadBufferMode;
 
+/*
+ * Type returned by PrefetchBuffer().
+ */
+typedef struct PrefetchBufferResult
+{
+	Buffer		recent_buffer;	/* If valid, a hit (recheck needed!) */
+	bool		initiated_io;	/* If true, a miss resulting in async I/O */
+} PrefetchBufferResult;
+
 /* forward declared, to avoid having to expose buf_internals.h here */
 struct WritebackContext;
 
@@ -162,8 +171,11 @@ extern PGDLLIMPORT int32 *LocalRefCount;
 /*
  * prototypes for functions in bufmgr.c
  */
-extern void PrefetchBuffer(Relation reln, ForkNumber forkNum,
-						   BlockNumber blockNum);
+extern PrefetchBufferResult PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln,
+												 ForkNumber forkNum,
+												 BlockNumber blockNum);
+extern PrefetchBufferResult PrefetchBuffer(Relation reln, ForkNumber forkNum,
+										   BlockNumber blockNum);
 extern Buffer ReadBuffer(Relation reln, BlockNumber blockNum);
 extern Buffer ReadBufferExtended(Relation reln, ForkNumber forkNum,
 								 BlockNumber blockNum, ReadBufferMode mode,
diff --git a/src/include/storage/md.h b/src/include/storage/md.h
index ec7630ce3b7..07fd1bb7d06 100644
--- a/src/include/storage/md.h
+++ b/src/include/storage/md.h
@@ -28,7 +28,7 @@ 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,
+extern bool mdprefetch(SMgrRelation reln, ForkNumber forknum,
 					   BlockNumber blocknum);
 extern void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 				   char *buffer);
diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index 79dfe0e373a..bb8428f27f6 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -93,7 +93,7 @@ extern void smgrdosyncall(SMgrRelation *rels, int nrels);
 extern void smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo);
 extern void smgrextend(SMgrRelation reln, ForkNumber forknum,
 					   BlockNumber blocknum, char *buffer, bool skipFsync);
-extern void smgrprefetch(SMgrRelation reln, ForkNumber forknum,
+extern bool smgrprefetch(SMgrRelation reln, ForkNumber forknum,
 						 BlockNumber blocknum);
 extern void smgrread(SMgrRelation reln, ForkNumber forknum,
 					 BlockNumber blocknum, char *buffer);