Patch: query_cache_with_comments

This patch adds an option to make the server ignore comments when checking for a query cache hit. For example pick these two queries:

/* first query  */ select name from users where users.name like 'Bob%';
/* retry search */ select name from users where users.name like 'Bob%';

By default (option disabled) the queries are considered different so the server will execute them both and cache them both.

If the option is enabled the queries are considered identical so the server will execute and cache the first one and will directly serve the second one from the query cache.

Makes the server ignore comments when checking for a query cache hit.

This patch add file

query_strip_comments.h

This file contain class QueryStripComments

class QueryStripComments
{
private:
  QueryStripComments(const QueryStripComments&);
  QueryStripComments& operator=(const QueryStripComments&);
public:
  QueryStripComments();
  ~QueryStripComments();
  void set(const char* a_query, uint a_query_length, uint a_additional_length);
  char* query()        { return buffer; }
  uint  query_length() { return length; }
};

In call

void set(const char* a_query, uint a_query_length, uint a_additional_length);

, QueryStripComments strip all comments and double-spaces from query length, save this in internal buffer, and also reserved plaсe for additional information. After

set

we can call

query and query_length

for access rewrited query.

If feature is enabled, set work as described above. If the feature disabled,

class QueryStripComments

simple map to arguments.

QueryStripComments is a member of

class THD

, file

sql/mysql_class.h

, and life time of this class equal life time of THD. On desctruction of member internal buffer was cleaned.

This class follow RAII and Scope guard idioms.

In call

QueryStripComments_Backup guard(thd,thd->query_script_comments)

instance of class call

thd->query_script_comments->set(thd->query(),thd->query_length());

and on call

QueryStripComments_Backup::~QueryStripComments_Backup()

(destruction of guard) instance was restore previous value query and query_length in THD.

MySQL query cache contain file

sql/sql_cache.cc

Function

send_result_to_client

. Before search this method write to query string, after the end additional information - database info, flags, so on. After it this buffer:

|/* first query  */ select name from users where users.name like 'Bob%';\0|database.name|flags|

uses as key for search in cache. This patch use

class QueryStripComments

for replace original query by striped query</code>.

This patch use

class QueryStripComments

and

class QueryStripComments_Backup

for replace original query by rewrited similar described in above.

RAII

Scope guard