From 6facd4cb13170e8695d9ae4f1e30611af0b0a472 Mon Sep 17 00:00:00 2001
From: Alexander Nozdrin <alik@sun.com>
Date: Fri, 14 May 2010 22:11:25 +0400
Subject: Patch for Bug#27863 (excessive memory usage for many small queries in
 a multiquery packet).

Background:

  - a query can contain multiple SQL statements;

  - the server frees resources allocated to process a query when the
    whole query is handled. In other words, resources allocated to process
    one SQL statement from a multi-statement query are freed when all SQL
    statements are handled.

The problem was that the parser allocated a buffer of size of the whole
query for each SQL statement in a multi-statement query. Thus, if a query
had many SQL-statements (so, the query was long), but each SQL statement
was short, ther parser tried to allocate huge amount of memory (number of
small SQL statements * length of the whole query).

The memory was allocated for a so-called "cpp buffer", which is intended to
store pre-processed SQL statement -- SQL text without version specific
comments.

The fix is to allocate memory for the "cpp buffer" once for all SQL
statements (once for a query).
---
 sql/sql_lex.h | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

(limited to 'sql/sql_lex.h')

diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 85ae2697f21..5230753e374 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -1377,6 +1377,8 @@ public:
   Lex_input_stream(THD *thd, const char* buff, unsigned int length);
   ~Lex_input_stream();
 
+  void reset(const char *buff, unsigned int length);
+
   /**
     Set the echo mode.
 
@@ -2206,8 +2208,8 @@ struct LEX: public Query_tables_list
 class Set_signal_information
 {
 public:
-  /** Constructor. */
-  Set_signal_information();
+  /** Empty default constructor, use clear() */
+ Set_signal_information() {} 
 
   /** Copy constructor. */
   Set_signal_information(const Set_signal_information& set);
@@ -2220,7 +2222,7 @@ public:
   void clear();
 
   /**
-    For each contition item assignment, m_item[] contains the parsed tree
+    For each condition item assignment, m_item[] contains the parsed tree
     that represents the expression assigned, if any.
     m_item[] is an array indexed by Diag_condition_item_name.
   */
@@ -2237,8 +2239,16 @@ class Yacc_state
 {
 public:
   Yacc_state()
-    : yacc_yyss(NULL), yacc_yyvs(NULL)
-  {}
+  {
+    reset();
+  }
+
+  void reset()
+  {
+    yacc_yyss= NULL;
+    yacc_yyvs= NULL;
+    m_set_signal_info.clear();
+  }
 
   ~Yacc_state();
 
@@ -2283,6 +2293,12 @@ public:
 
   Lex_input_stream m_lip;
   Yacc_state m_yacc;
+
+  void reset(const char *found_semicolon, unsigned int length)
+  {
+    m_lip.reset(found_semicolon, length);
+    m_yacc.reset();
+  }
 };
 
 
-- 
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