Improve inv_getsize() per suggestion from Denis Perchine; also fix

thinkos in inv_seek().

diff --git a/src/backend/storage/large_object/inv_api.c b/src/backend/storage/large_object/inv_api.c
index 607c4861dc58dba43c52e6a9dde1a490b12b0973..2c8e855dda2bbd9212cb73e4dd6bd26ad9fec286 100644 (file)
--- a/src/backend/storage/large_object/inv_api.c
+++ b/src/backend/storage/large_object/inv_api.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/storage/large_object/inv_api.c,v 1.79 2000/10/24 01:38:29 tgl Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/storage/large_object/inv_api.c,v 1.80 2000/11/02 23:52:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -186,7 +186,6 @@ inv_getsize(LargeObjectDesc *obj_desc)
 {
    bool            found = false;
    uint32          lastbyte = 0;
-   uint32          thislastbyte;
    ScanKeyData     skey[1];
    IndexScanDesc   sd;
    RetrieveIndexResult indexRes;
@@ -209,7 +208,13 @@ inv_getsize(LargeObjectDesc *obj_desc)
    tuple.t_datamcxt = CurrentMemoryContext;
    tuple.t_data = NULL;
 
-   while ((indexRes = index_getnext(sd, ForwardScanDirection)))
+   /*
+    * Because the pg_largeobject index is on both loid and pageno,
+    * but we constrain only loid, a backwards scan should visit all
+    * pages of the large object in reverse pageno order.  So, it's
+    * sufficient to examine the first valid tuple (== last valid page).
+    */
+   while ((indexRes = index_getnext(sd, BackwardScanDirection)))
    {
        tuple.t_self = indexRes->heap_iptr;
        heap_fetch(obj_desc->heap_r, SnapshotNow, &tuple, &buffer);
@@ -226,12 +231,11 @@ inv_getsize(LargeObjectDesc *obj_desc)
                heap_tuple_untoast_attr((varattrib *) datafield);
            pfreeit = true;
        }
-       thislastbyte = data->pageno * LOBLKSIZE + getbytealen(datafield);
-       if (thislastbyte > lastbyte)
-           lastbyte = thislastbyte;
+       lastbyte = data->pageno * LOBLKSIZE + getbytealen(datafield);
        if (pfreeit)
            pfree(datafield);
        ReleaseBuffer(buffer);
+       break;
    }
    
    index_endscan(sd);
@@ -254,16 +258,17 @@ inv_seek(LargeObjectDesc *obj_desc, int offset, int whence)
            obj_desc->offset = offset;
            break;
        case SEEK_CUR:
-           if ((obj_desc->offset + offset) < 0)
+           if (offset < 0 && obj_desc->offset < ((uint32) (- offset)))
                elog(ERROR, "inv_seek: invalid offset: %d", offset);
            obj_desc->offset += offset;
            break;
        case SEEK_END:
            {
-               uint32 size = inv_getsize(obj_desc);
-               if (offset < 0 || ((uint32) offset) > size)
-                   elog(ERROR, "inv_seek: invalid offset");
-               obj_desc->offset = size - offset;
+               uint32  size = inv_getsize(obj_desc);
+
+               if (offset < 0 && size < ((uint32) (- offset)))
+                   elog(ERROR, "inv_seek: invalid offset: %d", offset);
+               obj_desc->offset = size + offset;
            }
            break;
        default: