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MDEV-30164 System variable for default collations

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This patch adds a way to override default collations
(or "character set collations") for desired character sets.

The SQL standard says:
> Each collation known in an SQL-environment is applicable to one
> or more character sets, and for each character set, one or more
> collations are applicable to it, one of which is associated with
> it as its character set collation.

In MariaDB, character set collations has been hard-coded so far,
e.g. utf8mb4_general_ci has been a hard-coded character set collation
for utf8mb4.

This patch allows to override (globally per server, or per session)
character set collations, so for example, uca1400_ai_ci can be set as a
character set collation for Unicode character sets
(instead of compiled xxx_general_ci).

The array of overridden character set collations is stored in a new
(session and global) system variable @@character_set_collations and
can be set as a comma separated list of charset=collation pairs, e.g.:

SET @@character_set_collations='utf8mb3=uca1400_ai_ci,utf8mb4=uca1400_ai_ci';

The variable is empty by default, which mean use the hard-coded
character set collations (e.g. utf8mb4_general_ci for utf8mb4).

The variable can also be set globally by passing to the server startup command
line, and/or in my.cnf.
This commit is contained in:
Alexander Barkov
2022-12-14 18:46:27 +04:00
parent 584c2351de
commit 75f25e4ca7
59 changed files with 2228 additions and 111 deletions
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40
sql/sql_prepare.cc
View File

@ -226,6 +226,20 @@ private:
*/
MEM_ROOT main_mem_root;
sql_mode_t m_sql_mode;
THD::used_t m_prepare_time_thd_used_flags;
uint m_prepare_time_charset_collation_map_version;
bool check_charset_collation_map_version(THD *thd,
Reprepare_observer *observer)
{
if ((m_prepare_time_thd_used_flags & THD::CHARACTER_SET_COLLATIONS_USED) &&
m_prepare_time_charset_collation_map_version !=
thd->variables.character_set_collations.version())
{
observer->report_error(thd);
return true;
}
return false;
}
private:
bool set_db(const LEX_CSTRING *db);
bool set_parameters(String *expanded_query,
@ -3891,7 +3905,9 @@ Prepared_statement::Prepared_statement(THD *thd_arg)
iterations(0),
start_param(0),
read_types(0),
m_sql_mode(thd->variables.sql_mode)
m_sql_mode(thd->variables.sql_mode),
m_prepare_time_thd_used_flags(0),
m_prepare_time_charset_collation_map_version(0)
{
init_sql_alloc(key_memory_prepared_statement_main_mem_root,
&main_mem_root, thd_arg->variables.query_alloc_block_size,
@ -4274,6 +4290,9 @@ bool Prepared_statement::prepare(const char *packet, uint packet_len)
}
// The same format as for triggers to compare
hr_prepare_time= my_hrtime();
m_prepare_time_thd_used_flags= thd->used;
m_prepare_time_charset_collation_map_version=
thd->variables.character_set_collations.version();
DBUG_RETURN(error);
}
@ -4829,6 +4848,13 @@ Prepared_statement::swap_prepared_statement(Prepared_statement *copy)
/* Ditto */
swap_variables(LEX_CSTRING, db, copy->db);
swap_variables(uint,
m_prepare_time_charset_collation_map_version,
copy->m_prepare_time_charset_collation_map_version);
swap_variables(THD::used_t,
m_prepare_time_thd_used_flags,
copy->m_prepare_time_thd_used_flags);
DBUG_ASSERT(param_count == copy->param_count);
DBUG_ASSERT(thd == copy->thd);
last_error[0]= '\0';
@ -4872,6 +4898,9 @@ bool Prepared_statement::execute(String *expanded_query, bool open_cursor)
LEX_CSTRING stmt_db_name= db;
if (check_charset_collation_map_version(thd, thd->m_reprepare_observer))
return true;
status_var_increment(thd->status_var.com_stmt_execute);
if (flags & (uint) IS_IN_USE)
@ -4989,6 +5018,15 @@ bool Prepared_statement::execute(String *expanded_query, bool open_cursor)
MYSQL_QUERY_EXEC_START(thd->query(), thd->thread_id, thd->get_db(),
&thd->security_ctx->priv_user[0],
(char *) thd->security_ctx->host_or_ip, 1);
/*
Some thd->used flags are set only during PREPARE.
For example CHARACTER_SET_COLLATIONS_USED is in most cases
set during parsing only.
Mix PREPARE time thd->used flags to EXECUTE time thd->used flags,
e.g. to have the log event header write an optional chunk with
the @@character_set_collations map.
*/
thd->used|= m_prepare_time_thd_used_flags;
error= mysql_execute_command(thd, true);
MYSQL_QUERY_EXEC_DONE(error);
thd->update_server_status();