From: Ole John Aske
Date: May 3 2012 12:13pm
Subject: bzr push into mysql-5.5-cluster-7.2 branch (ole.john.aske:3908 to 3909)
List-Archive: http://lists.mysql.com/commits/143735
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 3909 Ole John Aske	2012-05-03
      ha_ndbcluster::read_first_row() was once implemented as part of the SPJ project
      as we then had plans for pushing queries with 'system' tables as root operation.
      (JT_SYSTEM is the only use case for ::read_first_row())
      
      It was later decided that we should not push such queries, but
      ha_ndbcluster::read_first_row() has remained in the code since then.
      
      There is a default implementation of this method (handler::read_first_row()) which
      is almost identical, except that it does not call ha_rnd_end() / ha_index_end()
      before returning. These calls was removed in our ha_ndbcluster::read_first_row()
      as pushed joins required the resultset to stay 'open' due to the child operations.
      
      However:
       - We do not push queries with 'system' tables so such a change
         is not required.
       - As part of fixing bug#13901890 'SQL NODE CRASHES DURING INSERT SELECT'
         we identified part of the root cause to be an overridden
         ::index_read_idx_map() which also omitted calling rnd_end()/index_end()
         before returning.
      
      This fix removes this obsolete, and potential evil code.

    modified:
      sql/ha_ndbcluster.cc
      sql/ha_ndbcluster.h
 3908 Ole John Aske	2012-05-03
      Backported some WL5940 related changes to 7.2-cluster:
      
        The handler extension ::test_push_flag() has now been removed.
        The two remaining HA_PUSH_<foo>-flags related to this extension
        has been made obsolete by:
      
        - HA_PUSH_BLOCK_CONST_TABLE is replaced with the 'test_flag'
          HA_BLOCK_CONST_TABLE. Furthermore it was identified that
          usage of this flag was obsolete at one of the places it was used.
          (As 'system' table optimization is not possible for handlers
           with non-EXACT statistics)
      
        - HA_PUSH_MULTIPLE_DEPENDENCY has been entirely removed as this
          covered a corner case with questionable advantage of being pushed.
          Previous changes to join_no_more_records() has been reverted.

    modified:
      mysql-test/suite/ndb/r/ndb_blob.result
      mysql-test/suite/ndb/r/ndb_dd_sql_features.result
      mysql-test/suite/ndb/r/ndb_join_pushdown_default.result
      sql/ha_ndbcluster.cc
      sql/ha_ndbcluster.h
      sql/ha_ndbcluster_push.cc
      sql/handler.h
      sql/sql_select.cc
=== modified file 'sql/ha_ndbcluster.cc'
--- a/sql/ha_ndbcluster.cc	2012-05-03 10:42:49 +0000
+++ b/sql/ha_ndbcluster.cc	2012-05-03 12:12:39 +0000
@@ -6568,46 +6568,6 @@ int ha_ndbcluster::index_read_last(uchar
 }
 
 
-/**
-  Read first row (only) from a table.
-
-  This is actually (yet) never called for ndbcluster tables, as these table types
-  does not set HA_STATS_RECORDS_IS_EXACT.
-
-  UPDATE: Might be called if the predicate contain '<column> IS NULL', and
-          <column> is defined as 'NOT NULL' (or is part of primary key)
-
-  Implemented regardless of this as the default implememtation would break 
-  any pushed joins as it calls ha_rnd_end() / ha_index_end() at end of execution.
-  */
-int ha_ndbcluster::read_first_row(uchar * buf, uint primary_key)
-{
-  register int error;
-  DBUG_ENTER("ha_ndbcluster::read_first_row");
-
-  ha_statistic_increment(&SSV::ha_read_first_count);
-
-  /*
-    If there is very few deleted rows in the table, find the first row by
-    scanning the table.
-    TODO remove the test for HA_READ_ORDER
-  */
-  if (stats.deleted < 10 || primary_key >= MAX_KEY ||
-      !(index_flags(primary_key, 0, 0) & HA_READ_ORDER))
-  {
-    (void) ha_rnd_init(1);
-    while ((error= rnd_next(buf)) == HA_ERR_RECORD_DELETED) ;
-  }
-  else
-  {
-    /* Find the first row through the primary key */
-    (void) ha_index_init(primary_key, 0);
-    error=index_first(buf);
-  }
-  DBUG_RETURN(error);
-}
-
-
 int ha_ndbcluster::read_range_first_to_buf(const key_range *start_key,
                                            const key_range *end_key,
                                            bool desc, bool sorted,

=== modified file 'sql/ha_ndbcluster.h'
--- a/sql/ha_ndbcluster.h	2012-05-03 10:42:49 +0000
+++ b/sql/ha_ndbcluster.h	2012-05-03 12:12:39 +0000
@@ -180,7 +180,6 @@ class ha_ndbcluster: public handler
   int rnd_next(uchar *buf);
   int rnd_pos(uchar *buf, uchar *pos);
   void position(const uchar *record);
-  int read_first_row(uchar *buf, uint primary_key);
   virtual int cmp_ref(const uchar * ref1, const uchar * ref2);
   int read_range_first(const key_range *start_key,
                        const key_range *end_key,

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