Postgres95 1.01 Distribution - Virgin Sources

src/backend/storage/buffer/buf_table.c

@@ -0,0 +1,162 @@
+/*-------------------------------------------------------------------------
+ *
+ * buf_table.c--
+ *    routines for finding buffers in the buffer pool.
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *    $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_table.c,v 1.1.1.1 1996/07/09 06:21:53 scrappy Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+/*
+ * OLD COMMENTS
+ *
+ * Data Structures:
+ *
+ *	Buffers are identified by their BufferTag (buf.h).  This
+ * file contains routines for allocating a shmem hash table to
+ * map buffer tags to buffer descriptors.
+ *
+ * Synchronization:
+ *  
+ *  All routines in this file assume buffer manager spinlock is
+ *  held by their caller.
+ */
+#include "storage/bufmgr.h"
+#include "storage/buf_internals.h"	/* where the declarations go */
+#include "storage/shmem.h"
+#include "storage/spin.h"
+#include "utils/hsearch.h"
+#include "utils/elog.h"
+
+static HTAB *SharedBufHash;
+
+extern HTAB *ShmemInitHash();
+
+typedef struct lookup { 
+    BufferTag	key; 
+    Buffer	id; 
+} LookupEnt;
+
+/*
+ * Initialize shmem hash table for mapping buffers
+ */
+void
+InitBufTable()
+{
+    HASHCTL info;
+    int hash_flags;
+    
+    /* assume lock is held */
+    
+    /* BufferTag maps to Buffer */
+    info.keysize = sizeof(BufferTag);
+    info.datasize = sizeof(Buffer);
+    info.hash = tag_hash;
+    
+    hash_flags = (HASH_ELEM | HASH_FUNCTION);
+    
+    
+    SharedBufHash = (HTAB *) ShmemInitHash("Shared Buf Lookup Table",
+					   NBuffers,NBuffers,
+					   &info,hash_flags);
+    
+    if (! SharedBufHash) {
+	elog(FATAL,"couldn't initialize shared buffer pool Hash Tbl");
+	exit(1);
+    }
+    
+}
+
+BufferDesc *
+BufTableLookup(BufferTag *tagPtr)
+{
+    LookupEnt *	result;
+    bool	found;
+    
+    if (tagPtr->blockNum == P_NEW)
+	return(NULL);
+    
+    result = (LookupEnt *) 
+	hash_search(SharedBufHash,(char *) tagPtr,HASH_FIND,&found);
+    
+    if (! result){
+	elog(WARN,"BufTableLookup: BufferLookup table corrupted");
+	return(NULL);
+    }
+    if (! found) {
+	return(NULL);
+    }
+    return(&(BufferDescriptors[result->id]));
+}
+
+/*
+ * BufTableDelete
+ */
+bool
+BufTableDelete(BufferDesc *buf)
+{
+    LookupEnt *	result;
+    bool	found;
+    
+    /* buffer not initialized or has been removed from
+     * table already.  BM_DELETED keeps us from removing 
+     * buffer twice.
+     */
+    if (buf->flags & BM_DELETED) {
+	return(TRUE);
+    }
+    
+    buf->flags |= BM_DELETED;
+    
+    result = (LookupEnt *)
+	hash_search(SharedBufHash,(char *) &(buf->tag),HASH_REMOVE,&found);
+    
+    if (! (result && found)) {
+	elog(WARN,"BufTableDelete: BufferLookup table corrupted");    
+	return(FALSE);
+    }
+    
+    return(TRUE);
+}
+
+bool
+BufTableInsert(BufferDesc *buf)
+{
+    LookupEnt *	result;
+    bool	found;
+    
+    /* cannot insert it twice */
+    Assert (buf->flags & BM_DELETED);
+    buf->flags &= ~(BM_DELETED);
+    
+    result = (LookupEnt *)
+	hash_search(SharedBufHash,(char *) &(buf->tag),HASH_ENTER,&found);
+    
+    if (! result) {
+	Assert(0);
+	elog(WARN,"BufTableInsert: BufferLookup table corrupted");
+	return(FALSE);
+    }
+    /* found something else in the table ! */
+    if (found) {
+	Assert(0);
+	elog(WARN,"BufTableInsert: BufferLookup table corrupted");
+	return(FALSE);
+    } 
+    
+    result->id = buf->buf_id;
+    return(TRUE);
+}
+
+/* prints out collision stats for the buf table */
+void
+DBG_LookupListCheck(int nlookup)
+{
+    nlookup = 10;
+    
+    hash_stats("Shared",SharedBufHash);
+}