Postgres95 1.01 Distribution - Virgin Sources

src/backend/access/nbtree/nbtscan.c

@@ -0,0 +1,164 @@
+/*-------------------------------------------------------------------------
+ *
+ * btscan.c--
+ *    manage scans on btrees.
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *    $Header: /cvsroot/pgsql/src/backend/access/nbtree/Attic/nbtscan.c,v 1.1.1.1 1996/07/09 06:21:12 scrappy Exp $
+ *
+ *
+ * NOTES
+ *   Because we can be doing an index scan on a relation while we update
+ *   it, we need to avoid missing data that moves around in the index.
+ *   The routines and global variables in this file guarantee that all
+ *   scans in the local address space stay correctly positioned.  This
+ *   is all we need to worry about, since write locking guarantees that
+ *   no one else will be on the same page at the same time as we are.
+ *
+ *   The scheme is to manage a list of active scans in the current backend.
+ *   Whenever we add or remove records from an index, or whenever we
+ *   split a leaf page, we check the list of active scans to see if any
+ *   has been affected.  A scan is affected only if it is on the same
+ *   relation, and the same page, as the update.
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "storage/bufmgr.h"
+#include "storage/bufpage.h"
+
+#include "utils/elog.h"
+#include "utils/palloc.h"
+#include "utils/rel.h"
+#include "utils/excid.h"
+
+#include "access/heapam.h"
+#include "access/genam.h"
+#include "access/sdir.h"
+#include "access/nbtree.h"
+
+typedef struct BTScanListData {
+    IndexScanDesc		btsl_scan;
+    struct BTScanListData	*btsl_next;
+} BTScanListData;
+
+typedef BTScanListData	*BTScanList;
+
+static BTScanList	BTScans = (BTScanList) NULL;
+     
+/*
+ *  _bt_regscan() -- register a new scan.
+ */
+void
+_bt_regscan(IndexScanDesc scan)
+{
+    BTScanList new_el;
+    
+    new_el = (BTScanList) palloc(sizeof(BTScanListData));
+    new_el->btsl_scan = scan;
+    new_el->btsl_next = BTScans;
+    BTScans = new_el;
+}
+
+/*
+ *  _bt_dropscan() -- drop a scan from the scan list
+ */
+void
+_bt_dropscan(IndexScanDesc scan)
+{
+    BTScanList chk, last;
+    
+    last = (BTScanList) NULL;
+    for (chk = BTScans;
+	 chk != (BTScanList) NULL && chk->btsl_scan != scan;
+	 chk = chk->btsl_next) {
+	last = chk;
+    }
+    
+    if (chk == (BTScanList) NULL)
+	elog(WARN, "btree scan list trashed; can't find 0x%lx", scan);
+    
+    if (last == (BTScanList) NULL)
+	BTScans = chk->btsl_next;
+    else
+	last->btsl_next = chk->btsl_next;
+    
+#ifdef PERFECT_MEM
+    pfree (chk);
+#endif /* PERFECT_MEM */
+}
+
+void
+_bt_adjscans(Relation rel, ItemPointer tid)
+{
+    BTScanList l;
+    Oid relid;
+    
+    relid = rel->rd_id;
+    for (l = BTScans; l != (BTScanList) NULL; l = l->btsl_next) {
+	if (relid == l->btsl_scan->relation->rd_id)
+	    _bt_scandel(l->btsl_scan, ItemPointerGetBlockNumber(tid),
+			ItemPointerGetOffsetNumber(tid));
+    }
+}
+
+void
+_bt_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno)
+{
+    ItemPointer current;
+    Buffer buf;
+    BTScanOpaque so;
+    
+    if (!_bt_scantouched(scan, blkno, offno))
+	return;
+    
+    so = (BTScanOpaque) scan->opaque;
+    buf = so->btso_curbuf;
+    
+    current = &(scan->currentItemData);
+    if (ItemPointerIsValid(current)
+	&& ItemPointerGetBlockNumber(current) == blkno
+	&& ItemPointerGetOffsetNumber(current) >= offno) {
+	_bt_step(scan, &buf, BackwardScanDirection);
+	so->btso_curbuf = buf;
+    }
+    
+    current = &(scan->currentMarkData);
+    if (ItemPointerIsValid(current)
+	&& ItemPointerGetBlockNumber(current) == blkno
+	&& ItemPointerGetOffsetNumber(current) >= offno) {
+	ItemPointerData tmp;
+	tmp = *current;
+	*current = scan->currentItemData;
+	scan->currentItemData = tmp;
+	_bt_step(scan, &buf, BackwardScanDirection);
+	so->btso_mrkbuf = buf;
+	tmp = *current;
+	*current = scan->currentItemData;
+	scan->currentItemData = tmp;
+    }
+}
+
+bool
+_bt_scantouched(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno)
+{
+    ItemPointer current;
+    
+    current = &(scan->currentItemData);
+    if (ItemPointerIsValid(current)
+	&& ItemPointerGetBlockNumber(current) == blkno
+	&& ItemPointerGetOffsetNumber(current) >= offno)
+	return (true);
+    
+    current = &(scan->currentMarkData);
+    if (ItemPointerIsValid(current)
+	&& ItemPointerGetBlockNumber(current) == blkno
+	&& ItemPointerGetOffsetNumber(current) >= offno)
+	return (true);
+    
+    return (false);
+}