ha_innodb.cc, row0sel.c, row0mysql.c, row0mysql.h:

  Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key

innobase/include/row0mysql.h

@@ -419,13 +419,21 @@ struct row_prebuilt_struct {
 					index where the ordering column is
 					the row id: in this case this flag
 					is set to TRUE */
-	dict_index_t*	index;		/* current index for a search, if any */
+	dict_index_t*	index;		/* current index for a search, if
+					any */
 	ulint		read_just_key;	/* set to 1 when MySQL calls
 					ha_innobase::extra with the
 					argument HA_EXTRA_KEYREAD; it is enough
 					to read just columns defined in
 					the index (i.e., no read of the
 					clustered index record necessary) */
+	ibool		used_in_HANDLER;/* TRUE if we have been using this
+					handle in a MySQL HANDLER low level
+					index cursor command: then we must
+					store the pcur position even in a
+					unique search from a clustered index,
+					because HANDLER allows NEXT and PREV
+					in such a situation */
 	ulint		template_type;	/* ROW_MYSQL_WHOLE_ROW, 
 					ROW_MYSQL_REC_FIELDS,
 					ROW_MYSQL_DUMMY_TEMPLATE, or

innobase/row/row0mysql.c

@@ -324,6 +324,9 @@ row_create_prebuilt(
 	prebuilt->mysql_has_locked = FALSE;
 
 	prebuilt->index = NULL;
+
+	prebuilt->used_in_HANDLER = FALSE;
+
 	prebuilt->n_template = 0;
 	prebuilt->mysql_template = NULL;
 

innobase/row/row0sel.c

@@ -2690,9 +2690,9 @@ row_search_for_mysql(
 
 		/* MySQL sometimes seems to do fetch next or fetch prev even
 		if the search condition is unique; this can, for example,
-		happen with the HANDLER commands; we do not store pcur position
-		in this case, so we cannot restore cursor position, and must
-		return immediately */
+		happen with the HANDLER commands; we do not always store the
+		pcur position in this case, so we cannot restore cursor
+		position, and must return immediately */
 
 		/* printf("%s record not found 1\n", index->name); */
 	
@@ -2703,13 +2703,13 @@ row_search_for_mysql(
 	mtr_start(&mtr);
 
 	/* In a search where at most one record in the index may match, we
-	can use a LOCK_REC_NOT_GAP type record lock when locking a non-delete
+	can use a LOCK_REC_NOT_GAP type record lock when locking a non-delete-
 	marked matching record.
 
-	Note that in a unique secondary index there may be different delete
+	Note that in a unique secondary index there may be different delete-
 	marked versions of a record where only the primary key values differ:
 	thus in a secondary index we must use next-key locks when locking
-	delete marked records. */
+	delete-marked records. */
 	
 	if (match_mode == ROW_SEL_EXACT
 	    && index->type & DICT_UNIQUE
@@ -2730,10 +2730,9 @@ row_search_for_mysql(
 	if (unique_search	
 	    && index->type & DICT_CLUSTERED
 	    && !prebuilt->templ_contains_blob
+	    && !prebuilt->used_in_HANDLER
 	    && (prebuilt->mysql_row_len < UNIV_PAGE_SIZE / 8)) {
 
-		ut_a(direction == 0);	/* We cannot do fetch prev, as we have
-					not stored the cursor position */
 		mode = PAGE_CUR_GE;
 
 		unique_search_from_clust_index = TRUE;
@@ -3217,11 +3216,16 @@ row_search_for_mysql(
 		}
 	}
 got_row:
-	/* TODO: should we in every case store the cursor position, even
-	if this is just a join, for example? */
+	/* We have an optimization to save CPU time: if this is a consistent
+	read on a unique condition on the clustered index, then we do not
+	store the pcur position, because any fetch next or prev will anyway
+	return 'end of file'. An exception is the MySQL HANDLER command
+	where the user can move the cursor with PREV or NEXT even after
+	a unique search. */
 
 	if (!unique_search_from_clust_index
-				|| prebuilt->select_lock_type == LOCK_X) {
+				|| prebuilt->select_lock_type == LOCK_X
+				|| prebuilt->used_in_HANDLER) {
 
 		/* Inside an update always store the cursor position */
 

sql/ha_innodb.cc

@@ -601,7 +601,7 @@ innobase_invalidate_query_cache(
 Call this when you have opened a new table handle in HANDLER, before you
 call index_read_idx() etc. Actually, we can let the cursor stay open even
 over a transaction commit! Then you should call this before every operation,
-fecth next etc. This function inits the necessary things even after a
+fetch next etc. This function inits the necessary things even after a
 transaction commit. */
 
 void
@@ -648,6 +648,8 @@ ha_innobase::init_table_handle_for_HANDLER(void)
 	we???? */
 
         prebuilt->read_just_key = FALSE;
+
+	prebuilt->used_in_HANDLER = TRUE;
 }
 
 /*************************************************************************
@@ -4048,6 +4050,8 @@ ha_innobase::external_lock(
 
 		  	trx->mysql_n_tables_locked = 0;
 
+			prebuilt->used_in_HANDLER = FALSE;
+
 			/* Here we release the search latch and InnoDB
 			thread FIFO ticket if they were reserved. */