Implement ORDER BY DESC optimization, which reads values in descending

order directly from the index instead of using a filesort.


mysql-test/mysql-test-run.sh:
  [ -n $SKIP_TEST ] --> [ -n "$SKIP_TEST" ]; portability fix
mysql-test/r/order_by.result:
  Added test for ORDER BY DESC optimization
mysql-test/t/order_by.test:
  Added test for ORDER BY DESC optimization
sql/opt_range.cc:
  Added QUICK_SELECT_DESC class which implements ORDER BY DESC optimization.
sql/opt_range.h:
  Added QUICK_SELECT_DESC class which implements ORDER BY DESC optimization.
sql/sql_select.cc:
  Added QUICK_SELECT_DESC class which implements ORDER BY DESC optimization.
BitKeeper/etc/ignore:
  Added .gdbinit .vimrc to the ignore list
BitKeeper/etc/logging_ok:
  Logging to logging@openlogging.org accepted

1 files changed, 14 insertions, 0 deletions

diff --git a/sql/opt_range.h b/sql/opt_range.h
index 247dd260817..0c8dcf7fed3 100644
--- a/sql/opt_range.h
+++ b/sql/opt_range.h
@@ -80,6 +80,20 @@ public:
   bool unique_key_range();
 };
 
+class QUICK_SELECT_DESC: public QUICK_SELECT
+{
+public:
+  QUICK_SELECT_DESC(QUICK_SELECT *q);
+  int get_next();
+private:
+  int cmp_prev(QUICK_RANGE *range);
+  bool range_reads_after_key(QUICK_RANGE *range);
+
+  QUICK_SELECT *quick;
+  List<QUICK_RANGE> rev_ranges;
+  List_iterator<QUICK_RANGE> rev_it;
+};
+
 class SQL_SELECT :public Sql_alloc {
  public:
   QUICK_SELECT *quick;		// If quick-select used