Implementation Details: query_cache_with_comments

This feature adds the souce code file:

query_strip_comments.h

This file defines the 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 strips all comments and double-spaces from the entire query, saves this in internal buffer [Oleg: “internal buffer” = the query cache?], and also reserves spaсe for additional information.

After

set

we can call

query and query_length

to access the rewritten query.

If the feature is enabled, SET works as described above. If the feature is 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 follows the 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 feature uses

class QueryStripComments

to replace the original query by the stripped query</code>.

This feature uses

class QueryStripComments

and

class QueryStripComments_Backup

to replace the original query by a similar rewriting to what was described above.