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).

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/ha_ndbcluster_binlog.cc b/sql/ha_ndbcluster_binlog.cc
index edb6aeebb5c..330891c1a10 100644
--- a/sql/ha_ndbcluster_binlog.cc
+++ b/sql/ha_ndbcluster_binlog.cc
@@ -263,7 +263,7 @@ static void run_query(THD *thd, char *buf, char *end,
   ulonglong save_thd_options= thd->variables.option_bits;
   DBUG_ASSERT(sizeof(save_thd_options) == sizeof(thd->variables.option_bits));
   NET save_thd_net= thd->net;
-  const char* found_semicolon= NULL;
+  Parser_state parser_state(thd, thd->query(), thd->query_length());
 
   bzero((char*) &thd->net, sizeof(NET));
   thd->set_query(buf, (uint) (end - buf));
@@ -277,7 +277,7 @@ static void run_query(THD *thd, char *buf, char *end,
   DBUG_ASSERT(!thd->in_sub_stmt);
   DBUG_ASSERT(!thd->locked_tables_mode);
 
-  mysql_parse(thd, thd->query(), thd->query_length(), &found_semicolon);
+  mysql_parse(thd, thd->query(), thd->query_length(), &parser_state);
 
   if (no_print_error && thd->is_slave_error)
   {