Ensure that all details of the ARC algorithm are hidden within freelist.c.

This refactoring does not change any algorithms or data structures, just
remove visibility of the ARC datastructures from other source files.

Author: tglsfdc

src/backend/storage/buffer/buf_init.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/buf_init.c,v 1.70 2004/12/31 22:00:49 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/buf_init.c,v 1.71 2005/02/03 23:29:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -73,7 +73,6 @@ long int	LocalBufferFlushCount;
  *		aborts, it should only unpin the buffers exactly the number of times it
  *		has pinned them, so that it will not blow away buffers of another
  *		backend.
- *
  */
 
 
@@ -120,14 +119,17 @@ InitBufferPool(void)
 		block = BufferBlocks;
 
 		/*
-		 * link the buffers into a single linked list. This will become
-		 * the LIFO list of unused buffers returned by
-		 * StrategyGetBuffer().
+		 * Initialize all the buffer headers.
 		 */
 		for (i = 0; i < NBuffers; block += BLCKSZ, buf++, i++)
 		{
 			Assert(ShmemIsValid((unsigned long) block));
 
+			/*
+			 * The bufNext fields link together all totally-unused buffers.
+			 * Subsequent management of this list is done by
+			 * StrategyGetBuffer().
+			 */
 			buf->bufNext = i + 1;
 
 			CLEAR_BUFFERTAG(buf->tag);
@@ -142,7 +144,7 @@ InitBufferPool(void)
 			buf->wait_backend_id = 0;
 		}
 
-		/* Correct last entry */
+		/* Correct last entry of linked list */
 		BufferDescriptors[NBuffers - 1].bufNext = -1;
 
 		LWLockRelease(BufMgrLock);
@@ -178,7 +180,8 @@ InitBufferPoolAccess(void)
 
 	/*
 	 * Convert shmem offsets into addresses as seen by this process. This
-	 * is just to speed up the BufferGetBlock() macro.
+	 * is just to speed up the BufferGetBlock() macro.  It is OK to do this
+	 * without any lock since the data pointers never change.
 	 */
 	for (i = 0; i < NBuffers; i++)
 		BufferBlockPointers[i] = (Block) MAKE_PTR(BufferDescriptors[i].data);
@@ -201,14 +204,8 @@ BufferShmemSize(void)
 	/* size of data pages */
 	size += NBuffers * MAXALIGN(BLCKSZ);
 
-	/* size of buffer hash table */
-	size += hash_estimate_size(NBuffers * 2, sizeof(BufferLookupEnt));
-
-	/* size of the shared replacement strategy control block */
-	size += MAXALIGN(sizeof(BufferStrategyControl));
-
-	/* size of the ARC directory blocks */
-	size += MAXALIGN(NBuffers * 2 * sizeof(BufferStrategyCDB));
+	/* size of stuff controlled by freelist.c */
+	size += StrategyShmemSize();
 
 	return size;
 }

src/backend/storage/buffer/buf_table.c

@@ -1,11 +1,11 @@
 /*-------------------------------------------------------------------------
  *
  * buf_table.c
- *	  routines for finding buffers in the buffer pool.
+ *	  routines for mapping BufferTags to buffer indexes.
  *
- * NOTE: these days, what this table actually provides is a mapping from
- * BufferTags to CDB indexes, not directly to buffers.	The function names
- * are thus slight misnomers.
+ * NOTE: this module is called only by freelist.c, and the "buffer IDs"
+ * it deals with are whatever freelist.c needs them to be; they may not be
+ * directly equivalent to Buffer numbers.
  *
  * Note: all routines in this file assume that the BufMgrLock is held
  * by the caller, so no synchronization is needed.
@@ -16,7 +16,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.38 2004/12/31 22:00:49 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.39 2005/02/03 23:29:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -26,12 +26,29 @@
 #include "storage/bufmgr.h"
 
 
+/* entry for buffer lookup hashtable */
+typedef struct
+{
+	BufferTag	key;			/* Tag of a disk page */
+	int			id;				/* Associated buffer ID */
+} BufferLookupEnt;
+
 static HTAB *SharedBufHash;
 
 
+/*
+ * Estimate space needed for mapping hashtable
+ *		size is the desired hash table size (possibly more than NBuffers)
+ */
+int
+BufTableShmemSize(int size)
+{
+	return hash_estimate_size(size, sizeof(BufferLookupEnt));
+}
+
 /*
  * Initialize shmem hash table for mapping buffers
- *		size is the desired hash table size (2*NBuffers for ARC algorithm)
+ *		size is the desired hash table size (possibly more than NBuffers)
  */
 void
 InitBufTable(int size)
@@ -56,7 +73,7 @@ InitBufTable(int size)
 
 /*
  * BufTableLookup
- *		Lookup the given BufferTag; return CDB index, or -1 if not found
+ *		Lookup the given BufferTag; return buffer ID, or -1 if not found
  */
 int
 BufTableLookup(BufferTag *tagPtr)
@@ -76,10 +93,10 @@ BufTableLookup(BufferTag *tagPtr)
 
 /*
  * BufTableInsert
- *		Insert a hashtable entry for given tag and CDB index
+ *		Insert a hashtable entry for given tag and buffer ID
  */
 void
-BufTableInsert(BufferTag *tagPtr, int cdb_id)
+BufTableInsert(BufferTag *tagPtr, int buf_id)
 {
 	BufferLookupEnt *result;
 	bool		found;
@@ -92,15 +109,15 @@ BufTableInsert(BufferTag *tagPtr, int cdb_id)
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of shared memory")));
 
-	if (found)					/* found something else in the table? */
+	if (found)					/* found something already in the table? */
 		elog(ERROR, "shared buffer hash table corrupted");
 
-	result->id = cdb_id;
+	result->id = buf_id;
 }
 
 /*
  * BufTableDelete
- *		Delete the hashtable entry for given tag
+ *		Delete the hashtable entry for given tag (which must exist)
  */
 void
 BufTableDelete(BufferTag *tagPtr)

src/backend/storage/buffer/freelist.c

@@ -3,6 +3,11 @@
  * freelist.c
  *	  routines for manipulating the buffer pool's replacement strategy.
  *
+ * The name "freelist.c" is now a bit of a misnomer, since this module
+ * controls not only the list of free buffers per se, but the entire
+ * mechanism for looking up existing shared buffers and the strategy
+ * for choosing replacement victims when needed.
+ *
  * Note: all routines in this file assume that the BufMgrLock is held
  * by the caller, so no synchronization is needed.
  *
@@ -12,7 +17,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/freelist.c,v 1.49 2004/12/31 22:00:49 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/freelist.c,v 1.50 2005/02/03 23:29:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,6 +30,51 @@
 #include "storage/bufmgr.h"
 
 
+/*
+ * Definitions for the buffer replacement strategy
+ */
+#define STRAT_LIST_UNUSED	(-1)
+#define STRAT_LIST_B1		0
+#define STRAT_LIST_T1		1
+#define STRAT_LIST_T2		2
+#define STRAT_LIST_B2		3
+#define STRAT_NUM_LISTS		4
+
+/*
+ * The Cache Directory Block (CDB) of the Adaptive Replacement Cache (ARC)
+ */
+typedef struct
+{
+	int			prev;			/* list links */
+	int			next;
+	short		list;			/* ID of list it is currently in */
+	bool		t1_vacuum;		/* t => present only because of VACUUM */
+	TransactionId t1_xid;		/* the xid this entry went onto T1 */
+	BufferTag	buf_tag;		/* page identifier */
+	int			buf_id;			/* currently assigned data buffer, or -1 */
+} BufferStrategyCDB;
+
+/*
+ * The shared ARC control information.
+ */
+typedef struct
+{
+	int			target_T1_size; /* What T1 size are we aiming for */
+	int			listUnusedCDB;	/* All unused StrategyCDB */
+	int			listHead[STRAT_NUM_LISTS];		/* ARC lists B1, T1, T2
+												 * and B2 */
+	int			listTail[STRAT_NUM_LISTS];
+	int			listSize[STRAT_NUM_LISTS];
+	Buffer		listFreeBuffers;	/* List of unused buffers */
+
+	long		num_lookup;		/* Some hit statistics */
+	long		num_hit[STRAT_NUM_LISTS];
+	time_t		stat_report;
+
+	/* Array of CDB's starts here */
+	BufferStrategyCDB cdb[1];	/* VARIABLE SIZE ARRAY */
+} BufferStrategyControl;
+
 /* GUC variable: time in seconds between statistics reports */
 int			DebugSharedBuffers = 0;
 
@@ -812,6 +862,28 @@ StrategyDirtyBufferList(BufferDesc **buffers, BufferTag *buftags,
 }
 
 
+/*
+ * StrategyShmemSize
+ *
+ * estimate the size of shared memory used by the freelist-related structures.
+ */
+int
+StrategyShmemSize(void)
+{
+	int			size = 0;
+
+	/* size of CDB lookup hash table */
+	size += BufTableShmemSize(NBuffers * 2);
+
+	/* size of the shared replacement strategy control block */
+	size += MAXALIGN(sizeof(BufferStrategyControl));
+
+	/* size of the ARC directory blocks */
+	size += MAXALIGN(NBuffers * 2 * sizeof(BufferStrategyCDB));
+
+	return size;
+}
+
 /*
  * StrategyInitialize -- initialize the buffer cache replacement
  *		strategy.