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: