mariadb/sql/event_data_objects.cc

/* Copyright (C) 2004-2006 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

#define MYSQL_LEX 1
#include "mysql_priv.h"
#include "events.h"
#include "event_data_objects.h"
#include "event_db_repository.h"
#include "sp_head.h"

/**
  @addtogroup Event_Scheduler
  @{
*/

/*************************************************************************/

/**
  Event_creation_ctx -- creation context of events.
*/

class Event_creation_ctx :public Stored_program_creation_ctx,
                          public Sql_alloc
{
public:
  static bool load_from_db(THD *thd,
                           MEM_ROOT *event_mem_root,
                           const char *db_name,
                           const char *event_name,
                           TABLE *event_tbl,
                           Stored_program_creation_ctx **ctx);

public:
  virtual Stored_program_creation_ctx *clone(MEM_ROOT *mem_root)
  {
    return new (mem_root)
               Event_creation_ctx(m_client_cs, m_connection_cl, m_db_cl);
  }

protected:
  virtual Object_creation_ctx *create_backup_ctx(THD *thd) const
  {
    /*
      We can avoid usual backup/restore employed in stored programs since we
      know that this is a top level statement and the worker thread is
      allocated exclusively to execute this event.
    */

    return NULL;
  }

private:
  Event_creation_ctx(CHARSET_INFO *client_cs,
                     CHARSET_INFO *connection_cl,
                     CHARSET_INFO *db_cl)
    : Stored_program_creation_ctx(client_cs, connection_cl, db_cl)
  { }
};

/**************************************************************************
  Event_creation_ctx implementation.
**************************************************************************/

bool
Event_creation_ctx::load_from_db(THD *thd,
                                 MEM_ROOT *event_mem_root,
                                 const char *db_name,
                                 const char *event_name,
                                 TABLE *event_tbl,
                                 Stored_program_creation_ctx **ctx)
{
  /* Load character set/collation attributes. */

  CHARSET_INFO *client_cs;
  CHARSET_INFO *connection_cl;
  CHARSET_INFO *db_cl;

  bool invalid_creation_ctx= FALSE;

  if (load_charset(event_mem_root,
                   event_tbl->field[ET_FIELD_CHARACTER_SET_CLIENT],
                   thd->variables.character_set_client,
                   &client_cs))
  {
    sql_print_warning("Event '%s'.'%s': invalid value "
                      "in column mysql.event.character_set_client.",
                      (const char *) db_name,
                      (const char *) event_name);

    invalid_creation_ctx= TRUE;
  }

  if (load_collation(event_mem_root,
                     event_tbl->field[ET_FIELD_COLLATION_CONNECTION],
                     thd->variables.collation_connection,
                     &connection_cl))
  {
    sql_print_warning("Event '%s'.'%s': invalid value "
                      "in column mysql.event.collation_connection.",
                      (const char *) db_name,
                      (const char *) event_name);

    invalid_creation_ctx= TRUE;
  }

  if (load_collation(event_mem_root,
                     event_tbl->field[ET_FIELD_DB_COLLATION],
                     NULL,
                     &db_cl))
  {
    sql_print_warning("Event '%s'.'%s': invalid value "
                      "in column mysql.event.db_collation.",
                      (const char *) db_name,
                      (const char *) event_name);

    invalid_creation_ctx= TRUE;
  }

  /*
    If we failed to resolve the database collation, load the default one
    from the disk.
  */

  if (!db_cl)
    db_cl= get_default_db_collation(thd, db_name);

  /* Create the context. */

  *ctx= new Event_creation_ctx(client_cs, connection_cl, db_cl);

  return invalid_creation_ctx;
}

/*************************************************************************/

/*
  Initiliazes dbname and name of an Event_queue_element_for_exec
  object

  SYNOPSIS
    Event_queue_element_for_exec::init()

  RETURN VALUE
    FALSE  OK
    TRUE   Error (OOM)
*/

bool
Event_queue_element_for_exec::init(LEX_STRING db, LEX_STRING n)
{
  if (!(dbname.str= my_strndup(db.str, dbname.length= db.length, MYF(MY_WME))))
    return TRUE;
  if (!(name.str= my_strndup(n.str, name.length= n.length, MYF(MY_WME))))
  {
    my_free((uchar*) dbname.str, MYF(0));
    return TRUE;
  }
  return FALSE;
}


/*
  Destructor

  SYNOPSIS
    Event_queue_element_for_exec::~Event_queue_element_for_exec()
*/

Event_queue_element_for_exec::~Event_queue_element_for_exec()
{
  my_free((uchar*) dbname.str, MYF(0));
  my_free((uchar*) name.str, MYF(0));
}


/*
  Constructor

  SYNOPSIS
    Event_basic::Event_basic()
*/

Event_basic::Event_basic()
{
  DBUG_ENTER("Event_basic::Event_basic");
  /* init memory root */
  init_alloc_root(&mem_root, 256, 512);
  dbname.str= name.str= NULL;
  dbname.length= name.length= 0;
  time_zone= NULL;
  DBUG_VOID_RETURN;
}


/*
  Destructor

  SYNOPSIS
    Event_basic::Event_basic()
*/

Event_basic::~Event_basic()
{
  DBUG_ENTER("Event_basic::~Event_basic");
  free_root(&mem_root, MYF(0));
  DBUG_VOID_RETURN;
}


/*
  Short function to load a char column into a LEX_STRING

  SYNOPSIS
    Event_basic::load_string_field()
      field_name  The field( enum_events_table_field is not actually used
                  because it's unknown in event_data_objects.h)
      fields      The Field array
      field_value The value
*/

bool
Event_basic::load_string_fields(Field **fields, ...)
{
  bool ret= FALSE;
  va_list args;
  enum enum_events_table_field field_name;
  LEX_STRING *field_value;

  DBUG_ENTER("Event_basic::load_string_fields");

  va_start(args, fields);
  field_name= (enum enum_events_table_field) va_arg(args, int);
  while (field_name < ET_FIELD_COUNT)
  {
    field_value= va_arg(args, LEX_STRING *);
    if ((field_value->str= get_field(&mem_root, fields[field_name])) == NullS)
    {
      ret= TRUE;
      break;
    }
    field_value->length= strlen(field_value->str);

    field_name= (enum enum_events_table_field) va_arg(args, int);
  }
  va_end(args);

  DBUG_RETURN(ret);
}


bool
Event_basic::load_time_zone(THD *thd, const LEX_STRING tz_name)
{
  String str(tz_name.str, &my_charset_latin1);
  time_zone= my_tz_find(thd, &str);

  return (time_zone == NULL);
}


/*
  Constructor

  SYNOPSIS
    Event_queue_element::Event_queue_element()
*/

Event_queue_element::Event_queue_element():
  status_changed(FALSE), last_executed_changed(FALSE),
  on_completion(Event_parse_data::ON_COMPLETION_DROP),
  status(Event_parse_data::ENABLED), expression(0), dropped(FALSE),
  execution_count(0)
{
  DBUG_ENTER("Event_queue_element::Event_queue_element");

  starts= ends= execute_at= last_executed= 0;
  starts_null= ends_null= execute_at_null= TRUE;

  DBUG_VOID_RETURN;
}


/*
  Destructor

  SYNOPSIS
    Event_queue_element::Event_queue_element()
*/
Event_queue_element::~Event_queue_element()
{
}


/*
  Constructor

  SYNOPSIS
    Event_timed::Event_timed()
*/

Event_timed::Event_timed():
  created(0), modified(0), sql_mode(0)
{
  DBUG_ENTER("Event_timed::Event_timed");
  init();
  DBUG_VOID_RETURN;
}


/*
  Destructor

  SYNOPSIS
    Event_timed::~Event_timed()
*/

Event_timed::~Event_timed()
{
}


/*
  Constructor

  SYNOPSIS
    Event_job_data::Event_job_data()
*/

Event_job_data::Event_job_data()
  :sql_mode(0)
{
}

/*
  Init all member variables

  SYNOPSIS
    Event_timed::init()
*/

void
Event_timed::init()
{
  DBUG_ENTER("Event_timed::init");

  definer_user.str= definer_host.str= body.str= comment.str= NULL;
  definer_user.length= definer_host.length= body.length= comment.length= 0;

  sql_mode= 0;

  DBUG_VOID_RETURN;
}


/**
  Load an event's body from a row from mysql.event.

  @details This method is silent on errors and should behave like that.
  Callers should handle throwing of error messages. The reason is that the
  class should not know about how to deal with communication.

  @return Operation status
    @retval FALSE OK
    @retval TRUE  Error
*/

bool
Event_job_data::load_from_row(THD *thd, TABLE *table)
{
  char *ptr;
  uint len;
  LEX_STRING tz_name;

  DBUG_ENTER("Event_job_data::load_from_row");

  if (!table)
    DBUG_RETURN(TRUE);

  if (table->s->fields < ET_FIELD_COUNT)
    DBUG_RETURN(TRUE);

  if (load_string_fields(table->field,
                         ET_FIELD_DB, &dbname,
                         ET_FIELD_NAME, &name,
                         ET_FIELD_BODY, &body,
                         ET_FIELD_DEFINER, &definer,
                         ET_FIELD_TIME_ZONE, &tz_name,
                         ET_FIELD_COUNT))
    DBUG_RETURN(TRUE);

  if (load_time_zone(thd, tz_name))
    DBUG_RETURN(TRUE);

  Event_creation_ctx::load_from_db(thd, &mem_root, dbname.str, name.str, table,
                                   &creation_ctx);

  ptr= strchr(definer.str, '@');

  if (! ptr)
    ptr= definer.str;

  len= ptr - definer.str;
  definer_user.str= strmake_root(&mem_root, definer.str, len);
  definer_user.length= len;
  len= definer.length - len - 1;
  /* 1:because of @ */
  definer_host.str= strmake_root(&mem_root, ptr + 1, len);
  definer_host.length= len;

  sql_mode= (ulong) table->field[ET_FIELD_SQL_MODE]->val_int();

  DBUG_RETURN(FALSE);
}


/**
  Load an event's body from a row from mysql.event.

  @details This method is silent on errors and should behave like that.
  Callers should handle throwing of error messages. The reason is that the
  class should not know about how to deal with communication.

  @return Operation status
    @retval FALSE OK
    @retval TRUE  Error
*/

bool
Event_queue_element::load_from_row(THD *thd, TABLE *table)
{
  char *ptr;
  MYSQL_TIME time;
  LEX_STRING tz_name;

  DBUG_ENTER("Event_queue_element::load_from_row");

  if (!table)
    DBUG_RETURN(TRUE);

  if (table->s->fields < ET_FIELD_COUNT)
    DBUG_RETURN(TRUE);

  if (load_string_fields(table->field,
                         ET_FIELD_DB, &dbname,
                         ET_FIELD_NAME, &name,
                         ET_FIELD_DEFINER, &definer,
                         ET_FIELD_TIME_ZONE, &tz_name,
                         ET_FIELD_COUNT))
    DBUG_RETURN(TRUE);

  if (load_time_zone(thd, tz_name))
    DBUG_RETURN(TRUE);

  starts_null= table->field[ET_FIELD_STARTS]->is_null();
  my_bool not_used= FALSE;
  if (!starts_null)
  {
    table->field[ET_FIELD_STARTS]->get_date(&time, TIME_NO_ZERO_DATE);
    starts= my_tz_OFFSET0->TIME_to_gmt_sec(&time,&not_used);
  }

  ends_null= table->field[ET_FIELD_ENDS]->is_null();
  if (!ends_null)
  {
    table->field[ET_FIELD_ENDS]->get_date(&time, TIME_NO_ZERO_DATE);
    ends= my_tz_OFFSET0->TIME_to_gmt_sec(&time,&not_used);
  }

  if (!table->field[ET_FIELD_INTERVAL_EXPR]->is_null())
    expression= table->field[ET_FIELD_INTERVAL_EXPR]->val_int();
  else
    expression= 0;
  /*
    If neigher STARTS and ENDS is set, then both fields are empty.
    Hence, if ET_FIELD_EXECUTE_AT is empty there is an error.
  */
  execute_at_null= table->field[ET_FIELD_EXECUTE_AT]->is_null();
  DBUG_ASSERT(!(starts_null && ends_null && !expression && execute_at_null));
  if (!expression && !execute_at_null)
  {
    if (table->field[ET_FIELD_EXECUTE_AT]->get_date(&time,
                                                    TIME_NO_ZERO_DATE))
      DBUG_RETURN(TRUE);
    execute_at= my_tz_OFFSET0->TIME_to_gmt_sec(&time,&not_used);
  }

  /*
    We load the interval type from disk as string and then map it to
    an integer. This decouples the values of enum interval_type
    and values actually stored on disk. Therefore the type can be
    reordered without risking incompatibilities of data between versions.
  */
  if (!table->field[ET_FIELD_TRANSIENT_INTERVAL]->is_null())
  {
    int i;
    char buff[MAX_FIELD_WIDTH];
    String str(buff, sizeof(buff), &my_charset_bin);
    LEX_STRING tmp;

    table->field[ET_FIELD_TRANSIENT_INTERVAL]->val_str(&str);
    if (!(tmp.length= str.length()))
      DBUG_RETURN(TRUE);

    tmp.str= str.c_ptr_safe();

    i= find_string_in_array(interval_type_to_name, &tmp, system_charset_info);
    if (i < 0)
      DBUG_RETURN(TRUE);
    interval= (interval_type) i;
  }

  if (!table->field[ET_FIELD_LAST_EXECUTED]->is_null())
  {
    table->field[ET_FIELD_LAST_EXECUTED]->get_date(&time,
                                                   TIME_NO_ZERO_DATE);
    last_executed= my_tz_OFFSET0->TIME_to_gmt_sec(&time,&not_used);
  }
  last_executed_changed= FALSE;

  if ((ptr= get_field(&mem_root, table->field[ET_FIELD_STATUS])) == NullS)
    DBUG_RETURN(TRUE);

  DBUG_PRINT("load_from_row", ("Event [%s] is [%s]", name.str, ptr));

  /* Set event status (ENABLED | SLAVESIDE_DISABLED | DISABLED) */
  switch (ptr[0])
  {
  case 'E' :
    status = Event_parse_data::ENABLED;
    break;
  case 'S' :
    status = Event_parse_data::SLAVESIDE_DISABLED;
    break;
  case 'D' :
  default:
    status = Event_parse_data::DISABLED;
    break;
  }
  if ((ptr= get_field(&mem_root, table->field[ET_FIELD_ORIGINATOR])) == NullS)
    DBUG_RETURN(TRUE);
  originator = table->field[ET_FIELD_ORIGINATOR]->val_int(); 

  /* ToDo : Andrey . Find a way not to allocate ptr on event_mem_root */
  if ((ptr= get_field(&mem_root,
                      table->field[ET_FIELD_ON_COMPLETION])) == NullS)
    DBUG_RETURN(TRUE);

  on_completion= (ptr[0]=='D'? Event_parse_data::ON_COMPLETION_DROP:
                               Event_parse_data::ON_COMPLETION_PRESERVE);

  DBUG_RETURN(FALSE);
}


/**
  Load an event's body from a row from mysql.event.

  @details This method is silent on errors and should behave like that.
  Callers should handle throwing of error messages. The reason is that the
  class should not know about how to deal with communication.

  @return Operation status
    @retval FALSE OK
    @retval TRUE  Error
*/

bool
Event_timed::load_from_row(THD *thd, TABLE *table)
{
  char *ptr;
  uint len;

  DBUG_ENTER("Event_timed::load_from_row");

  if (Event_queue_element::load_from_row(thd, table))
    DBUG_RETURN(TRUE);

  if (load_string_fields(table->field,
                         ET_FIELD_BODY, &body,
                         ET_FIELD_BODY_UTF8, &body_utf8,
                         ET_FIELD_COUNT))
    DBUG_RETURN(TRUE);

  if (Event_creation_ctx::load_from_db(thd, &mem_root, dbname.str, name.str,
                                       table, &creation_ctx))
  {
    push_warning_printf(thd,
                        MYSQL_ERROR::WARN_LEVEL_WARN,
                        ER_EVENT_INVALID_CREATION_CTX,
                        ER(ER_EVENT_INVALID_CREATION_CTX),
                        (const char *) dbname.str,
                        (const char *) name.str);
  }

  ptr= strchr(definer.str, '@');

  if (! ptr)
    ptr= definer.str;

  len= ptr - definer.str;
  definer_user.str= strmake_root(&mem_root, definer.str, len);
  definer_user.length= len;
  len= definer.length - len - 1;
  /* 1:because of @ */
  definer_host.str= strmake_root(&mem_root, ptr + 1,  len);
  definer_host.length= len;

  created= table->field[ET_FIELD_CREATED]->val_int();
  modified= table->field[ET_FIELD_MODIFIED]->val_int();

  comment.str= get_field(&mem_root, table->field[ET_FIELD_COMMENT]);
  if (comment.str != NullS)
    comment.length= strlen(comment.str);
  else
    comment.length= 0;

  sql_mode= (ulong) table->field[ET_FIELD_SQL_MODE]->val_int();

  DBUG_RETURN(FALSE);
}


/*
  add_interval() adds a specified interval to time 'ltime' in time
  zone 'time_zone', and returns the result converted to the number of
  seconds since epoch (aka Unix time; in UTC time zone).  Zero result
  means an error.
*/
static
my_time_t
add_interval(MYSQL_TIME *ltime, const Time_zone *time_zone,
             interval_type scale, INTERVAL interval)
{
  if (date_add_interval(ltime, scale, interval))
    return 0;

  my_bool not_used;
  return time_zone->TIME_to_gmt_sec(ltime, &not_used);
}


/*
  Computes the sum of a timestamp plus interval.

  SYNOPSIS
    get_next_time()
      time_zone     event time zone
      next          the sum
      start         add interval_value to this time
      time_now      current time
      i_value       quantity of time type interval to add
      i_type        type of interval to add (SECOND, MINUTE, HOUR, WEEK ...)

  RETURN VALUE
    0  OK
    1  Error

  NOTES
    1) If the interval is conversible to SECOND, like MINUTE, HOUR, DAY, WEEK.
       Then we use TIMEDIFF()'s implementation as underlying and number of
       seconds as resolution for computation.
    2) In all other cases - MONTH, QUARTER, YEAR we use MONTH as resolution
       and PERIOD_DIFF()'s implementation
*/

static
bool get_next_time(const Time_zone *time_zone, my_time_t *next,
                   my_time_t start, my_time_t time_now,
                   int i_value, interval_type i_type)
{
  DBUG_ENTER("get_next_time");
  DBUG_PRINT("enter", ("start: %lu  now: %lu", (long) start, (long) time_now));

  DBUG_ASSERT(start <= time_now);

  longlong months=0, seconds=0;

  switch (i_type) {
  case INTERVAL_YEAR:
    months= i_value*12;
    break;
  case INTERVAL_QUARTER:
    /* Has already been converted to months */
  case INTERVAL_YEAR_MONTH:
  case INTERVAL_MONTH:
    months= i_value;
    break;
  case INTERVAL_WEEK:
    /* WEEK has already been converted to days */
  case INTERVAL_DAY:
    seconds= i_value*24*3600;
    break;
  case INTERVAL_DAY_HOUR:
  case INTERVAL_HOUR:
    seconds= i_value*3600;
    break;
  case INTERVAL_DAY_MINUTE:
  case INTERVAL_HOUR_MINUTE:
  case INTERVAL_MINUTE:
    seconds= i_value*60;
    break;
  case INTERVAL_DAY_SECOND:
  case INTERVAL_HOUR_SECOND:
  case INTERVAL_MINUTE_SECOND:
  case INTERVAL_SECOND:
    seconds= i_value;
    break;
  case INTERVAL_DAY_MICROSECOND:
  case INTERVAL_HOUR_MICROSECOND:
  case INTERVAL_MINUTE_MICROSECOND:
  case INTERVAL_SECOND_MICROSECOND:
  case INTERVAL_MICROSECOND:
    /*
     We should return an error here so SHOW EVENTS/ SELECT FROM I_S.EVENTS
     would give an error then.
    */
    DBUG_RETURN(1);
    break;
  case INTERVAL_LAST:
    DBUG_ASSERT(0);
  }
  DBUG_PRINT("info", ("seconds: %ld  months: %ld", (long) seconds, (long) months));

  MYSQL_TIME local_start;
  MYSQL_TIME local_now;

  /* Convert times from UTC to local. */
  {
    time_zone->gmt_sec_to_TIME(&local_start, start);
    time_zone->gmt_sec_to_TIME(&local_now, time_now);
  }

  INTERVAL interval;
  bzero(&interval, sizeof(interval));
  my_time_t next_time= 0;

  if (seconds)
  {
    longlong seconds_diff;
    long microsec_diff;
    bool negative= calc_time_diff(&local_now, &local_start, 1,
                                  &seconds_diff, &microsec_diff);
    if (!negative)
    {
      /*
        The formula below returns the interval that, when added to
        local_start, will always give the time in the future.
      */
      interval.second= seconds_diff - seconds_diff % seconds + seconds;
      next_time= add_interval(&local_start, time_zone,
                              INTERVAL_SECOND, interval);
      if (next_time == 0)
        goto done;
    }

    if (next_time <= time_now)
    {
      /*
        If 'negative' is true above, then 'next_time == 0', and
        'next_time <= time_now' is also true.  If negative is false,
        then next_time was set, but perhaps to the value that is less
        then time_now.  See below for elaboration.
      */
      DBUG_ASSERT(negative || next_time > 0);

      /*
        If local_now < local_start, i.e. STARTS time is in the future
        according to the local time (it always in the past according
        to UTC---this is a prerequisite of this function), then
        STARTS is almost always in the past according to the local
        time too.  However, in the time zone that has backward
        Daylight Saving Time shift, the following may happen: suppose
        we have a backward DST shift at certain date after 2:59:59,
        i.e. local time goes 1:59:59, 2:00:00, ... , 2:59:59, (shift
        here) 2:00:00 (again), ... , 2:59:59 (again), 3:00:00, ... .
        Now suppose the time has passed the first 2:59:59, has been
        shifted backward, and now is (the second) 2:20:00.  The user
        does CREATE EVENT with STARTS 'current-date 2:40:00'.  Local
        time 2:40:00 from create statement is treated by time
        functions as the first such time, so according to UTC it comes
        before the second 2:20:00.  But according to local time it is
        obviously in the future, so we end up in this branch.

        Since we are in the second pass through 2:00:00--2:59:59, and
        any local time form this interval is treated by system
        functions as the time from the first pass, we have to find the
        time for the next execution that is past the DST-affected
        interval (past the second 2:59:59 for our example,
        i.e. starting from 3:00:00).  We do this in the loop until the
        local time is mapped onto future UTC time.  'start' time is in
        the past, so we may use 'do { } while' here, and add the first
        interval right away.

        Alternatively, it could be that local_now >= local_start.  Now
        for the example above imagine we do CREATE EVENT with STARTS
        'current-date 2:10:00'.  Local start 2:10 is in the past (now
        is local 2:20), so we add an interval, and get next execution
        time, say, 2:40.  It is in the future according to local time,
        but, again, since we are in the second pass through
        2:00:00--2:59:59, 2:40 will be converted into UTC time in the
        past.  So we will end up in this branch again, and may add
        intervals in a 'do { } while' loop.

        Note that for any given event we may end up here only if event
        next execution time will map to the time interval that is
        passed twice, and only if the server was started during the
        second pass, or the event is being created during the second
        pass.  After that, we never will get here (unless we again
        start the server during the second pass).  In other words,
        such a condition is extremely rare.
      */
      interval.second= seconds;
      do
      {
        next_time= add_interval(&local_start, time_zone,
                                INTERVAL_SECOND, interval);
        if (next_time == 0)
          goto done;
      }
      while (next_time <= time_now);
    }
  }
  else
  {
    long diff_months= (long) (local_now.year - local_start.year)*12 +
                      (local_now.month - local_start.month);
    /*
      Unlike for seconds above, the formula below returns the interval
      that, when added to the local_start, will give the time in the
      past, or somewhere in the current month.  We are interested in
      the latter case, to see if this time has already passed, or is
      yet to come this month.

      Note that the time is guaranteed to be in the past unless
      (diff_months % months == 0), but no good optimization is
      possible here, because (diff_months % months == 0) is what will
      happen most of the time, as get_next_time() will be called right
      after the execution of the event.  We could pass last_executed
      time to this function, and see if the execution has already
      happened this month, but for that we will have to convert
      last_executed from seconds since epoch to local broken-down
      time, and this will greatly reduce the effect of the
      optimization.  So instead we keep the code simple and clean.
    */
    interval.month= (ulong) (diff_months - diff_months % months);
    next_time= add_interval(&local_start, time_zone,
                            INTERVAL_MONTH, interval);
    if (next_time == 0)
      goto done;

    if (next_time <= time_now)
    {
      interval.month= (ulong) months;
      next_time= add_interval(&local_start, time_zone,
                              INTERVAL_MONTH, interval);
      if (next_time == 0)
        goto done;
    }
  }

  DBUG_ASSERT(time_now < next_time);

  *next= next_time;

done:
  DBUG_PRINT("info", ("next_time: %ld", (long) next_time));
  DBUG_RETURN(next_time == 0);
}


/*
  Computes next execution time.

  SYNOPSIS
    Event_queue_element::compute_next_execution_time()

  RETURN VALUE
    FALSE  OK
    TRUE   Error

  NOTES
    The time is set in execute_at, if no more executions the latter is
    set to 0.
*/

bool
Event_queue_element::compute_next_execution_time()
{
  my_time_t time_now;
  DBUG_ENTER("Event_queue_element::compute_next_execution_time");
  DBUG_PRINT("enter", ("starts: %lu  ends: %lu  last_executed: %lu  this: 0x%lx",
                       (long) starts, (long) ends, (long) last_executed,
                       (long) this));

  if (status != Event_parse_data::ENABLED)
  {
    DBUG_PRINT("compute_next_execution_time",
               ("Event %s is DISABLED", name.str));
    goto ret;
  }
  /* If one-time, no need to do computation */
  if (!expression)
  {
    /* Let's check whether it was executed */
    if (last_executed)
    {
      DBUG_PRINT("info",("One-time event %s.%s of was already executed",
                         dbname.str, name.str));
      dropped= (on_completion == Event_parse_data::ON_COMPLETION_DROP);
      DBUG_PRINT("info",("One-time event will be dropped: %d.", dropped));

      status= Event_parse_data::DISABLED;
      status_changed= TRUE;
    }
    goto ret;
  }

  time_now= (my_time_t) current_thd->query_start();

  DBUG_PRINT("info",("NOW: [%lu]", (ulong) time_now));

  /* if time_now is after ends don't execute anymore */
  if (!ends_null && ends < time_now)
  {
    DBUG_PRINT("info", ("NOW after ENDS, don't execute anymore"));
    /* time_now is after ends. don't execute anymore */
    execute_at= 0;
    execute_at_null= TRUE;
    if (on_completion == Event_parse_data::ON_COMPLETION_DROP)
      dropped= TRUE;
    DBUG_PRINT("info", ("Dropped: %d", dropped));
    status= Event_parse_data::DISABLED;
    status_changed= TRUE;

    goto ret;
  }

  /*
    Here time_now is before or equals ends if the latter is set.
    Let's check whether time_now is before starts.
    If so schedule for starts.
  */
  if (!starts_null && time_now <= starts)
  {
    if (time_now == starts && starts == last_executed)
    {
      /*
        do nothing or we will schedule for second time execution at starts.
      */
    }
    else
    {
      DBUG_PRINT("info", ("STARTS is future, NOW <= STARTS,sched for STARTS"));
      /*
        starts is in the future
        time_now before starts. Scheduling for starts
      */
      execute_at= starts;
      execute_at_null= FALSE;
      goto ret;
    }
  }

  if (!starts_null && !ends_null)
  {
    /*
      Both starts and m_ends are set and time_now is between them (incl.)
      If last_executed is set then increase with m_expression. The new MYSQL_TIME is
      after m_ends set execute_at to 0. And check for on_completion
      If not set then schedule for now.
    */
    DBUG_PRINT("info", ("Both STARTS & ENDS are set"));
    if (!last_executed)
    {
      DBUG_PRINT("info", ("Not executed so far."));
    }

    {
      my_time_t next_exec;

      if (get_next_time(time_zone, &next_exec, starts, time_now,
                        (int) expression, interval))
        goto err;

      /* There was previous execution */
      if (ends < next_exec)
      {
        DBUG_PRINT("info", ("Next execution of %s after ENDS. Stop executing.",
                   name.str));
        /* Next execution after ends. No more executions */
        execute_at= 0;
        execute_at_null= TRUE;
        if (on_completion == Event_parse_data::ON_COMPLETION_DROP)
          dropped= TRUE;
        status= Event_parse_data::DISABLED;
        status_changed= TRUE;
      }
      else
      {
        DBUG_PRINT("info",("Next[%lu]", (ulong) next_exec));
        execute_at= next_exec;
        execute_at_null= FALSE;
      }
    }
    goto ret;
  }
  else if (starts_null && ends_null)
  {
    /* starts is always set, so this is a dead branch !! */
    DBUG_PRINT("info", ("Neither STARTS nor ENDS are set"));
    /*
      Both starts and m_ends are not set, so we schedule for the next
      based on last_executed.
    */
    if (last_executed)
    {
      my_time_t next_exec;
      if (get_next_time(time_zone, &next_exec, starts, time_now,
                        (int) expression, interval))
        goto err;
      execute_at= next_exec;
      DBUG_PRINT("info",("Next[%lu]", (ulong) next_exec));
    }
    else
    {
      /* last_executed not set. Schedule the event for now */
      DBUG_PRINT("info", ("Execute NOW"));
      execute_at= time_now;
    }
    execute_at_null= FALSE;
  }
  else
  {
    /* either starts or m_ends is set */
    if (!starts_null)
    {
      DBUG_PRINT("info", ("STARTS is set"));
      /*
        - starts is set.
        - starts is not in the future according to check made before
        Hence schedule for starts + m_expression in case last_executed
        is not set, otherwise to last_executed + m_expression
      */
      if (!last_executed)
      {
        DBUG_PRINT("info", ("Not executed so far."));
      }

      {
        my_time_t next_exec;
        if (get_next_time(time_zone, &next_exec, starts, time_now,
                          (int) expression, interval))
          goto err;
        execute_at= next_exec;
        DBUG_PRINT("info",("Next[%lu]", (ulong) next_exec));
      }
      execute_at_null= FALSE;
    }
    else
    {
      /* this is a dead branch, because starts is always set !!! */
      DBUG_PRINT("info", ("STARTS is not set. ENDS is set"));
      /*
        - m_ends is set
        - m_ends is after time_now or is equal
        Hence check for m_last_execute and increment with m_expression.
        If last_executed is not set then schedule for now
      */

      if (!last_executed)
        execute_at= time_now;
      else
      {
        my_time_t next_exec;

        if (get_next_time(time_zone, &next_exec, starts, time_now,
                          (int) expression, interval))
          goto err;

        if (ends < next_exec)
        {
          DBUG_PRINT("info", ("Next execution after ENDS. Stop executing."));
          execute_at= 0;
          execute_at_null= TRUE;
          status= Event_parse_data::DISABLED;
          status_changed= TRUE;
          if (on_completion == Event_parse_data::ON_COMPLETION_DROP)
            dropped= TRUE;
        }
        else
        {
          DBUG_PRINT("info", ("Next[%lu]", (ulong) next_exec));
          execute_at= next_exec;
          execute_at_null= FALSE;
        }
      }
    }
    goto ret;
  }
ret:
  DBUG_PRINT("info", ("ret: 0 execute_at: %lu", (long) execute_at));
  DBUG_RETURN(FALSE);
err:
  DBUG_PRINT("info", ("ret=1"));
  DBUG_RETURN(TRUE);
}


/*
  Set the internal last_executed MYSQL_TIME struct to now. NOW is the
  time according to thd->query_start(), so the THD's clock.

  SYNOPSIS
    Event_queue_element::mark_last_executed()
      thd   thread context
*/

void
Event_queue_element::mark_last_executed(THD *thd)
{
  last_executed= (my_time_t) thd->query_start();
  last_executed_changed= TRUE;

  execution_count++;
}


/*
  Saves status and last_executed_at to the disk if changed.

  SYNOPSIS
    Event_queue_element::update_timing_fields()
      thd - thread context

  RETURN VALUE
    FALSE   OK
    TRUE    Error while opening mysql.event for writing or during
            write on disk
*/

bool
Event_queue_element::update_timing_fields(THD *thd)
{
  Event_db_repository *db_repository= Events::get_db_repository();
  int ret;

  DBUG_ENTER("Event_queue_element::update_timing_fields");

  DBUG_PRINT("enter", ("name: %*s", (int) name.length, name.str));

  /* No need to update if nothing has changed */
  if (!(status_changed || last_executed_changed))
    DBUG_RETURN(0);

  ret= db_repository->update_timing_fields_for_event(thd,
                                                     dbname, name,
                                                     last_executed_changed,
                                                     last_executed,
                                                     status_changed,
                                                     (ulonglong) status);
  last_executed_changed= status_changed= FALSE;
  DBUG_RETURN(ret);
}


static
void
append_datetime(String *buf, Time_zone *time_zone, my_time_t secs,
                const char *name, uint len)
{
  char dtime_buff[20*2+32];/* +32 to make my_snprintf_{8bit|ucs2} happy */
  buf->append(STRING_WITH_LEN(" "));
  buf->append(name, len);
  buf->append(STRING_WITH_LEN(" '"));
  /*
    Pass the buffer and the second param tells fills the buffer and
    returns the number of chars to copy.
  */
  MYSQL_TIME time;
  time_zone->gmt_sec_to_TIME(&time, secs);
  buf->append(dtime_buff, my_datetime_to_str(&time, dtime_buff));
  buf->append(STRING_WITH_LEN("'"));
}


/*
  Get SHOW CREATE EVENT as string

  SYNOPSIS
    Event_timed::get_create_event(THD *thd, String *buf)
      thd    Thread
      buf    String*, should be already allocated. CREATE EVENT goes inside.

  RETURN VALUE
    0                       OK
    EVEX_MICROSECOND_UNSUP  Error (for now if mysql.event has been
                            tampered and MICROSECONDS interval or
                            derivative has been put there.
*/

int
Event_timed::get_create_event(THD *thd, String *buf)
{
  char tmp_buf[2 * STRING_BUFFER_USUAL_SIZE];
  String expr_buf(tmp_buf, sizeof(tmp_buf), system_charset_info);
  expr_buf.length(0);

  DBUG_ENTER("get_create_event");
  DBUG_PRINT("ret_info",("body_len=[%d]body=[%s]",
                         (int) body.length, body.str));

  if (expression && Events::reconstruct_interval_expression(&expr_buf, interval,
                                                            expression))
    DBUG_RETURN(EVEX_MICROSECOND_UNSUP);

  buf->append(STRING_WITH_LEN("CREATE EVENT "));
  append_identifier(thd, buf, name.str, name.length);

  if (expression)
  {
    buf->append(STRING_WITH_LEN(" ON SCHEDULE EVERY "));
    buf->append(expr_buf);
    buf->append(' ');
    LEX_STRING *ival= &interval_type_to_name[interval];
    buf->append(ival->str, ival->length);

    if (!starts_null)
      append_datetime(buf, time_zone, starts, STRING_WITH_LEN("STARTS"));

    if (!ends_null)
      append_datetime(buf, time_zone, ends, STRING_WITH_LEN("ENDS"));
  }
  else
  {
    append_datetime(buf, time_zone, execute_at,
                    STRING_WITH_LEN("ON SCHEDULE AT"));
  }

  if (on_completion == Event_parse_data::ON_COMPLETION_DROP)
    buf->append(STRING_WITH_LEN(" ON COMPLETION NOT PRESERVE "));
  else
    buf->append(STRING_WITH_LEN(" ON COMPLETION PRESERVE "));

  if (status == Event_parse_data::ENABLED)
    buf->append(STRING_WITH_LEN("ENABLE"));
  else if (status == Event_parse_data::SLAVESIDE_DISABLED)
    buf->append(STRING_WITH_LEN("DISABLE ON SLAVE"));
  else
    buf->append(STRING_WITH_LEN("DISABLE"));

  if (comment.length)
  {
    buf->append(STRING_WITH_LEN(" COMMENT "));
    append_unescaped(buf, comment.str, comment.length);
  }
  buf->append(STRING_WITH_LEN(" DO "));
  buf->append(body.str, body.length);

  DBUG_RETURN(0);
}


/**
  Get an artificial stored procedure to parse as an event definition.
*/

bool
Event_job_data::construct_sp_sql(THD *thd, String *sp_sql)
{
  LEX_STRING buffer;
  const uint STATIC_SQL_LENGTH= 44;

  DBUG_ENTER("Event_job_data::construct_sp_sql");

  /*
    Allocate a large enough buffer on the thread execution memory
    root to avoid multiple [re]allocations on system heap
  */
  buffer.length= STATIC_SQL_LENGTH + name.length + body.length;
  if (! (buffer.str= (char*) thd->alloc(buffer.length)))
    DBUG_RETURN(TRUE);

  sp_sql->set(buffer.str, buffer.length, system_charset_info);
  sp_sql->length(0);


  sp_sql->append(C_STRING_WITH_LEN("CREATE "));
  sp_sql->append(C_STRING_WITH_LEN("PROCEDURE "));
  /*
    Let's use the same name as the event name to perhaps produce a
    better error message in case it is a part of some parse error.
    We're using append_identifier here to successfully parse
    events with reserved names.
  */
  append_identifier(thd, sp_sql, name.str, name.length);

  /*
    The default SQL security of a stored procedure is DEFINER. We
    have already activated the security context of the event, so
    let's execute the procedure with the invoker rights to save on
    resets of security contexts.
  */
  sp_sql->append(C_STRING_WITH_LEN("() SQL SECURITY INVOKER "));

  sp_sql->append(body.str, body.length);

  DBUG_RETURN(thd->is_fatal_error);
}


/**
  Get DROP EVENT statement to binlog the drop of ON COMPLETION NOT
  PRESERVE event.
*/

bool
Event_job_data::construct_drop_event_sql(THD *thd, String *sp_sql)
{
  LEX_STRING buffer;
  const uint STATIC_SQL_LENGTH= 14;

  DBUG_ENTER("Event_job_data::construct_drop_event_sql");

  buffer.length= STATIC_SQL_LENGTH + name.length*2 + dbname.length*2;
  if (! (buffer.str= (char*) thd->alloc(buffer.length)))
    DBUG_RETURN(TRUE);

  sp_sql->set(buffer.str, buffer.length, system_charset_info);
  sp_sql->length(0);

  sp_sql->append(C_STRING_WITH_LEN("DROP EVENT "));
  append_identifier(thd, sp_sql, dbname.str, dbname.length);
  sp_sql->append('.');
  append_identifier(thd, sp_sql, name.str, name.length);

  DBUG_RETURN(thd->is_fatal_error);
}

/**
  Compiles and executes the event (the underlying sp_head object)

  @retval TRUE  error (reported to the error log)
  @retval FALSE success
*/

bool
Event_job_data::execute(THD *thd, bool drop)
{
  String sp_sql;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
  Security_context event_sctx, *save_sctx= NULL;
#endif
  List<Item> empty_item_list;
  bool ret= TRUE;

  DBUG_ENTER("Event_job_data::execute");

  mysql_reset_thd_for_next_command(thd);

  /*
    MySQL parser currently assumes that current database is either
    present in THD or all names in all statements are fully specified.
    And yet not fully specified names inside stored programs must be 
    be supported, even if the current database is not set:
    CREATE PROCEDURE db1.p1() BEGIN CREATE TABLE t1; END//
    -- in this example t1 should be always created in db1 and the statement
    must parse even if there is no current database.

    To support this feature and still address the parser limitation,
    we need to set the current database here.
    We don't have to call mysql_change_db, since the checks performed
    in it are unnecessary for the purpose of parsing, and
    mysql_change_db will be invoked anyway later, to activate the
    procedure database before it's executed.
  */
  thd->set_db(dbname.str, dbname.length);

#ifndef NO_EMBEDDED_ACCESS_CHECKS
  if (event_sctx.change_security_context(thd,
                                         &definer_user, &definer_host,
                                         &dbname, &save_sctx))
  {
    sql_print_error("Event Scheduler: "
                    "[%s].[%s.%s] execution failed, "
                    "failed to authenticate the user.",
                    definer.str, dbname.str, name.str);
    goto end_no_lex_start;
  }
#endif

  if (check_access(thd, EVENT_ACL, dbname.str,
                   0, 0, 0, is_schema_db(dbname.str)))
  {
    /*
      This aspect of behavior is defined in the worklog,
      and this is how triggers work too: if TRIGGER
      privilege is revoked from trigger definer,
      triggers are not executed.
    */
    sql_print_error("Event Scheduler: "
                    "[%s].[%s.%s] execution failed, "
                    "user no longer has EVENT privilege.",
                    definer.str, dbname.str, name.str);
    goto end_no_lex_start;
  }

  if (construct_sp_sql(thd, &sp_sql))
    goto end_no_lex_start;

  /*
    Set up global thread attributes to reflect the properties of
    this Event. We can simply reset these instead of usual
    backup/restore employed in stored programs since we know that
    this is a top level statement and the worker thread is
    allocated exclusively to execute this event.
  */

  thd->variables.sql_mode= sql_mode;
  thd->variables.time_zone= time_zone;

  /*
    Peculiar initialization order is a crutch to avoid races in SHOW
    PROCESSLIST which reads thd->{query/query_length} without a mutex.
  */
  thd->query_length= 0;
  thd->query= sp_sql.c_ptr_safe();
  thd->query_length= sp_sql.length();

  {
    Lex_input_stream lip(thd, thd->query, thd->query_length);
    lex_start(thd);

    if (parse_sql(thd, &lip, creation_ctx))
    {
      sql_print_error("Event Scheduler: "
                      "%serror during compilation of %s.%s",
                      thd->is_fatal_error ? "fatal " : "",
                      (const char *) dbname.str, (const char *) name.str);
      goto end;
    }
  }

  {
    sp_head *sphead= thd->lex->sphead;

    DBUG_ASSERT(sphead);

    if (thd->enable_slow_log)
      sphead->m_flags|= sp_head::LOG_SLOW_STATEMENTS;
    sphead->m_flags|= sp_head::LOG_GENERAL_LOG;

    sphead->set_info(0, 0, &thd->lex->sp_chistics, sql_mode);
    sphead->set_creation_ctx(creation_ctx);
    sphead->optimize();

    ret= sphead->execute_procedure(thd, &empty_item_list);
    /*
      There is no pre-locking and therefore there should be no
      tables open and locked left after execute_procedure.
    */
  }

end:
  if (thd->lex->sphead)                        /* NULL only if a parse error */
  {
    delete thd->lex->sphead;
    thd->lex->sphead= NULL;
  }

end_no_lex_start:
  if (drop && !thd->is_fatal_error)
  {
    /*
      We must do it here since here we're under the right authentication
      ID of the event definer.
    */
    sql_print_information("Event Scheduler: Dropping %s.%s",
                          (const char *) dbname.str, (const char *) name.str);
    /*
      Construct a query for the binary log, to ensure the event is dropped
      on the slave
    */
    if (construct_drop_event_sql(thd, &sp_sql))
      ret= 1;
    else
    {
      ulong saved_master_access;
      /*
        Peculiar initialization order is a crutch to avoid races in SHOW
        PROCESSLIST which reads thd->{query/query_length} without a mutex.
      */
      thd->query_length= 0;
      thd->query= sp_sql.c_ptr_safe();
      thd->query_length= sp_sql.length();

      /*
        NOTE: even if we run in read-only mode, we should be able to lock
        the mysql.event table for writing. In order to achieve this, we
        should call mysql_lock_tables() under the super-user.
      */

      saved_master_access= thd->security_ctx->master_access;
      thd->security_ctx->master_access |= SUPER_ACL;

      ret= Events::drop_event(thd, dbname, name, FALSE);

      thd->security_ctx->master_access= saved_master_access;
    }
  }
#ifndef NO_EMBEDDED_ACCESS_CHECKS
  if (save_sctx)
    event_sctx.restore_security_context(thd, save_sctx);
#endif
  lex_end(thd->lex);
  thd->lex->unit.cleanup();
  thd->end_statement();
  thd->cleanup_after_query();
  /* Avoid races with SHOW PROCESSLIST */
  thd->query_length= 0;
  thd->query= NULL;

  DBUG_PRINT("info", ("EXECUTED %s.%s  ret: %d", dbname.str, name.str, ret));

  DBUG_RETURN(ret);
}


/*
  Checks whether two events are in the same schema

  SYNOPSIS
    event_basic_db_equal()
      db  Schema
      et  Compare et->dbname to `db`

  RETURN VALUE
    TRUE   Equal
    FALSE  Not equal
*/

bool
event_basic_db_equal(LEX_STRING db, Event_basic *et)
{
  return !sortcmp_lex_string(et->dbname, db, system_charset_info);
}


/*
  Checks whether an event has equal `db` and `name`

  SYNOPSIS
    event_basic_identifier_equal()
      db   Schema
      name Name
      et   The event object

  RETURN VALUE
    TRUE   Equal
    FALSE  Not equal
*/

bool
event_basic_identifier_equal(LEX_STRING db, LEX_STRING name, Event_basic *b)
{
  return !sortcmp_lex_string(name, b->name, system_charset_info) &&
         !sortcmp_lex_string(db, b->dbname, system_charset_info);
}

/**
  @} (End of group Event_Scheduler)
*/