[Commits] Rev 3556: Better comments in file:///home/psergey/dev2/5.3-look5/

Sergey Petrunya psergey at askmonty.org
Tue Aug 21 21:24:35 EEST 2012


At file:///home/psergey/dev2/5.3-look5/

------------------------------------------------------------
revno: 3556
revision-id: psergey at askmonty.org-20120821182434-v4qwqc82ptql3v5m
parent: igor at askmonty.org-20120814212556-jr7fdqpm89ooyvdz
committer: Sergey Petrunya <psergey at askmonty.org>
branch nick: 5.3-look5
timestamp: Tue 2012-08-21 22:24:34 +0400
message:
  Better comments
=== modified file 'sql/opt_subselect.cc'
--- a/sql/opt_subselect.cc	2012-06-05 14:25:10 +0000
+++ b/sql/opt_subselect.cc	2012-08-21 18:24:34 +0000
@@ -143,18 +143,18 @@
   3.2.1 Non-merged semi-joins and join optimization
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   For join optimization purposes, non-merged semi-join nests are similar to
-  base tables - they've got one JOIN_TAB, which can be accessed with one of
-  two methods:
+  base tables. Each such nest is represented by one one JOIN_TAB, which has 
+  two possible access strategies:
    - full table scan (representing SJ-Materialization-Scan strategy)
    - eq_ref-like table lookup (representing SJ-Materialization-Lookup)
 
   Unlike regular base tables, non-merged semi-joins have:
    - non-zero JOIN_TAB::startup_cost, and
    - join_tab->table->is_filled_at_execution()==TRUE, which means one
-     cannot do const table detection or range analysis or other table data-
-     dependent inferences
-  // instead, get_delayed_table_estimates() runs optimization on the nest so that 
-  // we get an idea about temptable size
+     cannot do const table detection, range analysis or other dataset-dependent
+     optimizations.
+     Instead, get_delayed_table_estimates() will run optimization for the
+     subquery and produce an E(materialized table size).
   
   3.2.2 Merged semi-joins and join optimization
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



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