Upgrade localbuf.c to use a hash table instead of linear search to

find already-allocated local buffers.  This is the last obstacle
in the way of setting NLocBuffer to something reasonably large.

src/backend/storage/buffer/localbuf.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.64 2005/03/18 16:16:09 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/localbuf.c,v 1.65 2005/03/19 17:39:43 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,18 +18,24 @@
 #include "storage/buf_internals.h"
 #include "storage/bufmgr.h"
 #include "storage/smgr.h"
-#include "utils/relcache.h"
+#include "utils/memutils.h"
 #include "utils/resowner.h"
 
 
 /*#define LBDEBUG*/
 
+/* entry for buffer lookup hashtable */
+typedef struct
+{
+	BufferTag	key;			/* Tag of a disk page */
+	int			id;				/* Associated local buffer's index */
+} LocalBufferLookupEnt;
+
 /* Note: this macro only works on local buffers, not shared ones! */
 #define LocalBufHdrGetBlock(bufHdr)	\
 	LocalBufferBlockPointers[-((bufHdr)->buf_id + 2)]
 
-/* should be a GUC parameter some day */
-int			NLocBuffer = 64;
+int			NLocBuffer = 0;		/* until buffers are initialized */
 
 BufferDesc *LocalBufferDescriptors = NULL;
 Block	   *LocalBufferBlockPointers = NULL;
@@ -37,10 +43,12 @@ int32	   *LocalRefCount = NULL;
 
 static int	nextFreeLocalBuf = 0;
 
+static HTAB *LocalBufHash = NULL;
+
 
 /*
  * LocalBufferAlloc -
- *	  allocate a local buffer. We do round robin allocation for now.
+ *	  Find or create a local buffer for the given page of the given relation.
  *
  * API is similar to bufmgr.c's BufferAlloc, except that we do not need
  * to do any locking since this is all local.	Also, IO_IN_PROGRESS
@@ -50,35 +58,39 @@ BufferDesc *
 LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
 {
 	BufferTag	newTag;			/* identity of requested block */
-	int			i;
-	int			trycounter;
+	LocalBufferLookupEnt *hresult;
 	BufferDesc *bufHdr;
+	int			b;
+	int			trycounter;
+	bool		found;
 
 	INIT_BUFFERTAG(newTag, reln, blockNum);
 
-	/* a low tech search for now -- should use a hashtable */
-	for (i = 0; i < NLocBuffer; i++)
+	/* See if the desired buffer already exists */
+	hresult = (LocalBufferLookupEnt *)
+		hash_search(LocalBufHash, (void *) &newTag, HASH_FIND, NULL);
+
+	if (hresult)
 	{
-		bufHdr = &LocalBufferDescriptors[i];
-		if (BUFFERTAGS_EQUAL(bufHdr->tag, newTag))
-		{
+		b = hresult->id;
+		bufHdr = &LocalBufferDescriptors[b];
+		Assert(BUFFERTAGS_EQUAL(bufHdr->tag, newTag));
 #ifdef LBDEBUG
-			fprintf(stderr, "LB ALLOC (%u,%d) %d\n",
-					RelationGetRelid(reln), blockNum, -i - 1);
+		fprintf(stderr, "LB ALLOC (%u,%d) %d\n",
+				RelationGetRelid(reln), blockNum, -b - 1);
 #endif
 
-			LocalRefCount[i]++;
-			ResourceOwnerRememberBuffer(CurrentResourceOwner,
-									  BufferDescriptorGetBuffer(bufHdr));
-			if (bufHdr->flags & BM_VALID)
-				*foundPtr = TRUE;
-			else
-			{
-				/* Previous read attempt must have failed; try again */
-				*foundPtr = FALSE;
-			}
-			return bufHdr;
+		LocalRefCount[b]++;
+		ResourceOwnerRememberBuffer(CurrentResourceOwner,
+									BufferDescriptorGetBuffer(bufHdr));
+		if (bufHdr->flags & BM_VALID)
+			*foundPtr = TRUE;
+		else
+		{
+			/* Previous read attempt must have failed; try again */
+			*foundPtr = FALSE;
 		}
+		return bufHdr;
 	}
 
 #ifdef LBDEBUG
@@ -93,7 +105,7 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
 	trycounter = NLocBuffer;
 	for (;;)
 	{
-		int			b = nextFreeLocalBuf;
+		b = nextFreeLocalBuf;
 
 		if (++nextFreeLocalBuf >= NLocBuffer)
 			nextFreeLocalBuf = 0;
@@ -136,31 +148,50 @@ LocalBufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr)
 				  (char *) LocalBufHdrGetBlock(bufHdr),
 				  true);
 
+		/* Mark not-dirty now in case we error out below */
+		bufHdr->flags &= ~BM_DIRTY;
+
 		LocalBufferFlushCount++;
 	}
 
 	/*
 	 * lazy memory allocation: allocate space on first use of a buffer.
-	 *
-	 * Note this path cannot be taken for a buffer that was previously in
-	 * use, so it's okay to do it (and possibly error out) before marking
-	 * the buffer as not dirty.
 	 */
 	if (LocalBufHdrGetBlock(bufHdr) == NULL)
 	{
-		char	   *data = (char *) malloc(BLCKSZ);
+		char	   *data;
 
-		if (data == NULL)
-			ereport(ERROR,
-					(errcode(ERRCODE_OUT_OF_MEMORY),
-					 errmsg("out of memory")));
+		data = (char *) MemoryContextAlloc(TopMemoryContext, BLCKSZ);
 
-		/*
-		 * Set pointer for use by BufferGetBlock() macro.
-		 */
+		/* Set pointer for use by BufferGetBlock() macro */
 		LocalBufHdrGetBlock(bufHdr) = (Block) data;
 	}
 
+	/*
+	 * Update the hash table: remove old entry, if any, and make new one.
+	 */
+	if (bufHdr->flags & BM_TAG_VALID)
+	{
+		hresult = (LocalBufferLookupEnt *)
+			hash_search(LocalBufHash, (void *) &bufHdr->tag,
+						HASH_REMOVE, NULL);
+		if (!hresult)				/* shouldn't happen */
+			elog(ERROR, "local buffer hash table corrupted");
+		/* mark buffer invalid just in case hash insert fails */
+		CLEAR_BUFFERTAG(bufHdr->tag);
+		bufHdr->flags &= ~(BM_VALID | BM_TAG_VALID);
+	}
+
+	hresult = (LocalBufferLookupEnt *)
+		hash_search(LocalBufHash, (void *) &newTag, HASH_ENTER, &found);
+	if (!hresult)
+		ereport(ERROR,
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("out of memory")));
+	if (found)				/* shouldn't happen */
+		elog(ERROR, "local buffer hash table corrupted");
+	hresult->id = b;
+
 	/*
 	 * it's all ours now.
 	 */
@@ -215,20 +246,39 @@ WriteLocalBuffer(Buffer buffer, bool release)
 void
 InitLocalBuffer(void)
 {
+	int			nbufs = 64;		/* should be from a GUC var */
+	HASHCTL		info;
 	int			i;
 
-	/*
-	 * these aren't going away. I'm not gonna use palloc.
-	 */
+	/* Create the lookup hash table */
+	MemSet(&info, 0, sizeof(info));
+	info.keysize = sizeof(BufferTag);
+	info.entrysize = sizeof(LocalBufferLookupEnt);
+	info.hash = tag_hash;
+
+	LocalBufHash = hash_create("Local Buffer Lookup Table",
+							   nbufs,
+							   &info,
+							   HASH_ELEM | HASH_FUNCTION);
+
+	if (!LocalBufHash)
+		elog(ERROR, "could not initialize local buffer hash table");
+
+	/* Allocate and zero buffer headers and auxiliary arrays */
 	LocalBufferDescriptors = (BufferDesc *)
-		calloc(NLocBuffer, sizeof(*LocalBufferDescriptors));
+		MemoryContextAllocZero(TopMemoryContext,
+							   nbufs * sizeof(BufferDesc));
 	LocalBufferBlockPointers = (Block *)
-		calloc(NLocBuffer, sizeof(*LocalBufferBlockPointers));
+		MemoryContextAllocZero(TopMemoryContext,
+							   nbufs * sizeof(Block));
 	LocalRefCount = (int32 *)
-		calloc(NLocBuffer, sizeof(*LocalRefCount));
+		MemoryContextAllocZero(TopMemoryContext,
+							   nbufs * sizeof(int32));
+
 	nextFreeLocalBuf = 0;
 
-	for (i = 0; i < NLocBuffer; i++)
+	/* initialize fields that need to start off nonzero */
+	for (i = 0; i < nbufs; i++)
 	{
 		BufferDesc *buf = &LocalBufferDescriptors[i];
 
@@ -240,6 +290,9 @@ InitLocalBuffer(void)
 		 */
 		buf->buf_id = -i - 2;
 	}
+
+	/* Initialization done, mark buffers allocated */
+	NLocBuffer = nbufs;
 }
 
 /*
@@ -271,5 +324,6 @@ void
 AtProcExit_LocalBuffers(void)
 {
 	/* just zero the refcounts ... */
-	MemSet(LocalRefCount, 0, NLocBuffer * sizeof(*LocalRefCount));
+	if (LocalRefCount)
+		MemSet(LocalRefCount, 0, NLocBuffer * sizeof(*LocalRefCount));
 }