WL#3984 (Revise locking of mysql.general_log and mysql.slow_log)

Bug#25422 (Hang with log tables)
Bug 17876 (Truncating mysql.slow_log in a SP after using cursor locks the
          thread)
Bug 23044 (Warnings on flush of a log table)
Bug 29129 (Resetting general_log while the GLOBAL READ LOCK is set causes
           a deadlock)

Prior to this fix, the server would hang when performing concurrent
ALTER TABLE or TRUNCATE TABLE statements against the LOG TABLES,
which are mysql.general_log and mysql.slow_log.

The root cause traces to the following code:
in sql_base.cc, open_table()
  if (table->in_use != thd)
  {
    /* wait_for_condition will unlock LOCK_open for us */
    wait_for_condition(thd, &LOCK_open, &COND_refresh);
  }
The problem with this code is that the current implementation of the
LOGGER creates 'fake' THD objects, like
- Log_to_csv_event_handler::general_log_thd
- Log_to_csv_event_handler::slow_log_thd
which are not associated to a real thread running in the server,
so that waiting for these non-existing threads to release table locks
cause the dead lock.

In general, the design of Log_to_csv_event_handler does not fit into the
general architecture of the server, so that the concept of general_log_thd
and slow_log_thd has to be abandoned:
- this implementation does not work with table locking
- it will not work with commands like SHOW PROCESSLIST
- having the log tables always opened does not integrate well with DDL
operations / FLUSH TABLES / SET GLOBAL READ_ONLY

With this patch, the fundamental design of the LOGGER has been changed to:
- always open and close a log table when writing a log
- remove totally the usage of fake THD objects
- clarify how locking of log tables is implemented in general.

See WL#3984 for details related to the new locking design.

Additional changes (misc bugs exposed and fixed):

1)

mysqldump which would ignore some tables in dump_all_tables_in_db(),
 but forget to ignore the same in dump_all_views_in_db().

2)

mysqldump would also issue an empty "LOCK TABLE" command when all the tables
to lock are to be ignored (numrows == 0), instead of not issuing the query.

3)

Internal errors handlers could intercept errors but not warnings
(see sql_error.cc).

4)

Implementing a nested call to open tables, for the performance schema tables,
exposed an existing bug in remove_table_from_cache(), which would perform:
  in_use->some_tables_deleted=1;
against another thread, without any consideration about thread locking.
This call inside remove_table_from_cache() was not required anyway,
since calling mysql_lock_abort() takes care of aborting -- cleanly -- threads
that might hold a lock on a table.
This line (in_use->some_tables_deleted=1) has been removed.

2 files changed, 1 insertions, 40 deletions

diff --git a/storage/myisam/ha_myisam.cc b/storage/myisam/ha_myisam.cc
index c86459ae0a7..77334b2cfba 100644
--- a/storage/myisam/ha_myisam.cc
+++ b/storage/myisam/ha_myisam.cc
@@ -607,41 +607,7 @@ err:
 #endif /* HAVE_REPLICATION */
 
 
-bool ha_myisam::check_if_locking_is_allowed(uint sql_command,
-                                            ulong type, TABLE *table,
-                                            uint count, uint current,
-                                            uint *system_count,
-                                            bool called_by_privileged_thread)
-{
-  /*
-    To be able to open and lock for reading system tables like 'mysql.proc',
-    when we already have some tables opened and locked, and avoid deadlocks
-    we have to disallow write-locking of these tables with any other tables.
-  */
-  if (table->s->system_table &&
-      table->reginfo.lock_type >= TL_WRITE_ALLOW_WRITE)
-    (*system_count)++;
-
-  /* 'current' is an index, that's why '<=' below. */
-  if (*system_count > 0 && *system_count <= current)
-  {
-    my_error(ER_WRONG_LOCK_OF_SYSTEM_TABLE, MYF(0));
-    return FALSE;
-  }
-
-  /*
-    Deny locking of the log tables, which is incompatible with
-    concurrent insert. Unless called from a logger THD (general_log_thd
-    or slow_log_thd) or by a privileged thread.
-  */
-  if (!called_by_privileged_thread)
-    return check_if_log_table_locking_is_allowed(sql_command, type, table);
-
-  return TRUE;
-}
-
-	/* Name is here without an extension */
-
+/* Name is here without an extension */
 int ha_myisam::open(const char *name, int mode, uint test_if_locked)
 {
   MI_KEYDEF *keyinfo;
diff --git a/storage/myisam/ha_myisam.h b/storage/myisam/ha_myisam.h
index 024675075c2..635f314b3da 100644
--- a/storage/myisam/ha_myisam.h
+++ b/storage/myisam/ha_myisam.h
@@ -60,11 +60,6 @@ class ha_myisam: public handler
   uint max_supported_key_part_length() const { return MI_MAX_KEY_LENGTH; }
   uint checksum() const;
 
-  virtual bool check_if_locking_is_allowed(uint sql_command,
-                                           ulong type, TABLE *table,
-                                           uint count, uint current,
-                                           uint *system_count,
-                                           bool called_by_logger_thread);
   int open(const char *name, int mode, uint test_if_locked);
   int close(void);
   int write_row(uchar * buf);