• konstantin@mysql.com's avatar
    A fix and a test case for · 117b76a5
    konstantin@mysql.com authored
     Bug#19022 "Memory bug when switching db during trigger execution"
     Bug#17199 "Problem when view calls function from another database."
     Bug#18444 "Fully qualified stored function names don't work correctly in
                SELECT statements"
    
     Documentation note: this patch introduces a change in behaviour of prepared
     statements.
    
     This patch adds a few new invariants with regard to how THD::db should
     be used. These invariants should be preserved in future:
    
      - one should never refer to THD::db by pointer and always make a deep copy
        (strmake, strdup)
      - one should never compare two databases by pointer, but use strncmp or
        my_strncasecmp
      - TABLE_LIST object table->db should be always initialized in the parser or
        by creator of the object.
    
        For prepared statements it means that if the current database is changed
        after a statement is prepared, the database that was current at prepare
        remains active. This also means that you can not prepare a statement that
        implicitly refers to the current database if the latter is not set.
        This is not documented, and therefore needs documentation. This is NOT a
        change in behavior for almost all SQL statements except:
         - ALTER TABLE t1 RENAME t2 
         - OPTIMIZE TABLE t1
         - ANALYZE TABLE t1
         - TRUNCATE TABLE t1 --
         until this patch t1 or t2 could be evaluated at the first execution of
         prepared statement. 
    
         CURRENT_DATABASE() still works OK and is evaluated at every execution
         of prepared statement.
    
         Note, that in stored routines this is not an issue as the default
         database is the database of the stored procedure and "use" statement
         is prohibited in stored routines.
    
      This patch makes obsolete the use of check_db_used (it was never used in the
      old code too) and all other places that check for table->db and assign it
      from THD::db if it's NULL, except the parser.
    
     How this patch was created: THD::{db,db_length} were replaced with a
     LEX_STRING, THD::db. All the places that refer to THD::{db,db_length} were
     manually checked and:
      - if the place uses thd->db by pointer, it was fixed to make a deep copy
      - if a place compared two db pointers, it was fixed to compare them by value
        (via strcmp/my_strcasecmp, whatever was approproate)
     Then this intermediate patch was used to write a smaller patch that does the
     same thing but without a rename.
    
     TODO in 5.1:
       - remove check_db_used
       - deploy THD::set_db in mysql_change_db
    
     See also comments to individual files.
    117b76a5
sp.h 3.57 KB