intermediate

Author: Daniel Shelepanov

engine.c

@@ -672,9 +672,39 @@ ptrack_walkdir(const char *path, Oid tablespaceOid, Oid dbOid)
 	FreeDir(dir);				/* we ignore any error here */
 }
 
+/*
+ * Get a second position within ptrack map so that it fits 
+ * within the same cache line.
+ */
+size_t
+get_slot2(size_t slot1, uint64 hash) {
+	size_t		cache_line_ep;	// ending point of a cache line
+	size_t		cache_line_sp;	// starting point of a cache line
+	size_t		cache_line_interval;
+	size_t		slot2;
+
+	/* Get the ending point of a cache line within entries[]. */
+	cache_line_ep = (CACHE_LINE_ALIGN(offsetof(PtrackMapHdr, entries) + slot1*sizeof(XLogRecPtr))
+			- offsetof(PtrackMapHdr, entries)) / sizeof(XLogRecPtr);
+	/* handling an overflow beyond the entries boundary */
+	cache_line_ep = cache_line_ep > PtrackContentNblocks ? PtrackContentNblocks : cache_line_ep;
+
+	/* Get the starting point of a cache line within entries[]. */
+	cache_line_sp = cache_line_ep - ENTRIES_PER_LINE;
+
+	/* Handling overflow below zero (sp then must be larger than ep) */
+	cache_line_sp = cache_line_sp > cache_line_ep ? 0 : cache_line_sp;
+
+	cache_line_interval = cache_line_ep - cache_line_sp;
+	slot2 = (size_t)(cache_line_sp + (((hash << 32) | (hash >> 32)) % cache_line_interval));
+	slot2 = (slot1 == slot2) ? ((slot1+1) % cache_line_interval) : slot2;
+	return slot2;
+}
+
 /*
  * Mark modified block in ptrack_map.
  */
+
 void
 ptrack_mark_block(RelFileNodeBackend smgr_rnode,
 				  ForkNumber forknum, BlockNumber blocknum)
@@ -703,7 +733,7 @@ ptrack_mark_block(RelFileNodeBackend smgr_rnode,
 
 	hash = BID_HASH_FUNC(bid);
 	slot1 = (size_t)(hash % PtrackContentNblocks);
-	slot2 = (size_t)(((hash << 32) | (hash >> 32)) % PtrackContentNblocks);
+	slot2 = get_slot2(slot1, hash);
 
 	if (RecoveryInProgress())
 		new_lsn = GetXLogReplayRecPtr(NULL);

engine.h

@@ -40,6 +40,14 @@
  */
 #define PTRACK_BUF_SIZE ((uint64) 8000)
 
+/*
+ * A reasonable assumption for most systems. Postgres core
+ * leverages the same value for this purpose.
+ */
+#define CACHE_LINE_SIZE	64
+#define CACHE_LINE_ALIGN(LEN)	TYPEALIGN(CACHE_LINE_SIZE, (LEN))
+#define ENTRIES_PER_LINE		(CACHE_LINE_SIZE/sizeof(XLogRecPtr))
+
 /* Ptrack magic bytes */
 #define PTRACK_MAGIC "ptk"
 #define PTRACK_MAGIC_SIZE 4
@@ -117,6 +125,7 @@ extern void ptrack_mark_block(RelFileNodeBackend smgr_rnode,
 							  ForkNumber forkno, BlockNumber blkno);
 
 extern bool is_cfm_file_path(const char *path);
+extern size_t get_slot2(size_t slot1, uint64 hash);
 #ifdef PGPRO_EE
 extern off_t    get_cfs_relation_file_decompressed_size(RelFileNodeBackend rnode,
 					const char *fullpath, ForkNumber forknum);

ptrack.c

@@ -651,7 +651,7 @@ ptrack_get_pagemapset(PG_FUNCTION_ARGS)
 		/* Only probe the second slot if the first one is marked */
 		if (update_lsn1 >= ctx->lsn)
 		{
-			slot2 = (size_t)(((hash << 32) | (hash >> 32)) % PtrackContentNblocks);
+			slot2 = get_slot2(slot1, hash);
 			update_lsn2 = pg_atomic_read_u64(&ptrack_map->entries[slot2]);
 
 			if (update_lsn2 != InvalidXLogRecPtr)