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Patch for Bug#27863 (excessive memory usage for many small queries in a

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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).
This commit is contained in:
Alexander Nozdrin
2010-05-14 22:11:25 +04:00
parent 4333980a49
commit 6facd4cb13
8 changed files with 103 additions and 60 deletions
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2
sql/sql_parse.h
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@ -84,7 +84,7 @@ bool is_log_table_write_query(enum enum_sql_command command);
bool alloc_query(THD *thd, const char *packet, uint packet_length);
void mysql_init_select(LEX *lex);
void mysql_parse(THD *thd, const char *inBuf, uint length,
const char ** semicolon);
Parser_state *parser_state);
void mysql_reset_thd_for_next_command(THD *thd);
bool mysql_new_select(LEX *lex, bool move_down);
void create_select_for_variable(const char *var_name);