mariadb/sql/sql_truncate.cc

/* Copyright (c) 2010, 2015, Oracle and/or its affiliates.
   Copyright (c) 2012, 2018, MariaDB

   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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */

#include "mariadb.h"
#include "debug_sync.h"  // DEBUG_SYNC
#include "table.h"       // TABLE, FOREIGN_KEY_INFO
#include "sql_class.h"   // THD
#include "sql_base.h"    // open_and_lock_tables
#include "sql_table.h"   // write_bin_log
#include "datadict.h"    // dd_recreate_table()
#include "lock.h"        // MYSQL_OPEN_* flags
#include "sql_acl.h"     // DROP_ACL
#include "sql_parse.h"   // check_one_table_access()
#include "sql_truncate.h"
#include "wsrep_mysqld.h"
#include "sql_show.h"    //append_identifier()
#include "sql_select.h"
#include "sql_delete.h"

/**
  Append a list of field names to a string.

  @param  str     The string.
  @param  fields  The list of field names.

  @return TRUE on failure, FALSE otherwise.
*/

static bool fk_info_append_fields(THD *thd, String *str,
                                  List<LEX_CSTRING> *fields)
{
  bool res= FALSE;
  LEX_CSTRING *field;
  List_iterator_fast<LEX_CSTRING> it(*fields);

  while ((field= it++))
  {
    res|= append_identifier(thd, str, field);
    res|= str->append(", ");
  }

  str->chop();
  str->chop();

  return res;
}


/**
  Generate a foreign key description suitable for a error message.

  @param thd          Thread context.
  @param fk_info   The foreign key information.

  @return A human-readable string describing the foreign key.
*/

static const char *fk_info_str(THD *thd, FOREIGN_KEY_INFO *fk_info)
{
  bool res= FALSE;
  char buffer[STRING_BUFFER_USUAL_SIZE*2];
  String str(buffer, sizeof(buffer), system_charset_info);

  str.length(0);

  /*
    `db`.`tbl`, CONSTRAINT `id` FOREIGN KEY (`fk`) REFERENCES `db`.`tbl` (`fk`)
  */

  res|= append_identifier(thd, &str, fk_info->foreign_db);
  res|= str.append(".");
  res|= append_identifier(thd, &str, fk_info->foreign_table);
  res|= str.append(", CONSTRAINT ");
  res|= append_identifier(thd, &str, fk_info->foreign_id);
  res|= str.append(" FOREIGN KEY (");
  res|= fk_info_append_fields(thd, &str, &fk_info->foreign_fields);
  res|= str.append(") REFERENCES ");
  res|= append_identifier(thd, &str, fk_info->referenced_db);
  res|= str.append(".");
  res|= append_identifier(thd, &str, fk_info->referenced_table);
  res|= str.append(" (");
  res|= fk_info_append_fields(thd, &str, &fk_info->referenced_fields);
  res|= str.append(')');

  return res ? NULL : thd->strmake(str.ptr(), str.length());
}


/**
  Check and emit a fatal error if the table which is going to be
  affected by TRUNCATE TABLE is a parent table in some non-self-
  referencing foreign key.

  @remark The intention is to allow truncate only for tables that
          are not dependent on other tables.

  @param  thd    Thread context.
  @param  table  Table handle.

  @retval FALSE  This table is not parent in a non-self-referencing foreign
                 key. Statement can proceed.
  @retval TRUE   This table is parent in a non-self-referencing foreign key,
                 error was emitted.
*/

static bool
fk_truncate_illegal_if_parent(THD *thd, TABLE *table)
{
  FOREIGN_KEY_INFO *fk_info;
  List<FOREIGN_KEY_INFO> fk_list;
  List_iterator_fast<FOREIGN_KEY_INFO> it;

  /*
    Bail out early if the table is not referenced by a foreign key.
    In this case, the table could only be, if at all, a child table.
  */
  if (! table->file->referenced_by_foreign_key())
    return FALSE;

  /*
    This table _is_ referenced by a foreign key. At this point, only
    self-referencing keys are acceptable. For this reason, get the list
    of foreign keys referencing this table in order to check the name
    of the child (dependent) tables.
  */
  table->file->get_parent_foreign_key_list(thd, &fk_list);

  /* Out of memory when building list. */
  if (unlikely(thd->is_error()))
    return TRUE;

  it.init(fk_list);

  /* Loop over the set of foreign keys for which this table is a parent. */
  while ((fk_info= it++))
  {
    if (lex_string_cmp(system_charset_info, fk_info->referenced_db,
                       &table->s->db) ||
        lex_string_cmp(system_charset_info, fk_info->referenced_table,
                       &table->s->table_name) ||
        lex_string_cmp(system_charset_info, fk_info->foreign_db,
                       &table->s->db) ||
        lex_string_cmp(system_charset_info, fk_info->foreign_table,
                       &table->s->table_name))
      break;
  }

  /* Table is parent in a non-self-referencing foreign key. */
  if (fk_info)
  {
    my_error(ER_TRUNCATE_ILLEGAL_FK, MYF(0), fk_info_str(thd, fk_info));
    return TRUE;
  }

  return FALSE;
}


/*
  Open and truncate a locked table.

  @param  thd           Thread context.
  @param  table_ref     Table list element for the table to be truncated.
  @param  is_tmp_table  True if element refers to a temp table.

  @retval TRUNCATE_OK   Truncate was successful and statement can be safely
                        binlogged.
  @retval TRUNCATE_FAILED_BUT_BINLOG Truncate failed but still go ahead with
                        binlogging as in case of non transactional tables
                        partial truncation is possible.

  @retval TRUNCATE_FAILED_SKIP_BINLOG Truncate was not successful hence donot
                        binlong the statement.
*/

enum Sql_cmd_truncate_table::truncate_result
Sql_cmd_truncate_table::handler_truncate(THD *thd, TABLE_LIST *table_ref,
                                         bool is_tmp_table)
{
  int error= 0;
  uint flags= 0;
  DBUG_ENTER("Sql_cmd_truncate_table::handler_truncate");

  /*
    Can't recreate, the engine must mechanically delete all rows
    in the table. Use open_and_lock_tables() to open a write cursor.
  */

  /* If it is a temporary table, no need to take locks. */
  if (!is_tmp_table)
  {
    /* We don't need to load triggers. */
    DBUG_ASSERT(table_ref->trg_event_map == 0);
    /*
      Our metadata lock guarantees that no transaction is reading
      or writing into the table. Yet, to open a write cursor we need
      a thr_lock lock. Allow to open base tables only.
    */
    table_ref->required_type= TABLE_TYPE_NORMAL;
    /*
      Ignore pending FLUSH TABLES since we don't want to release
      the MDL lock taken above and otherwise there is no way to
      wait for FLUSH TABLES in deadlock-free fashion.
    */
    flags= MYSQL_OPEN_IGNORE_FLUSH;
    /*
      Even though we have an MDL lock on the table here, we don't
      pass MYSQL_OPEN_HAS_MDL_LOCK to open_and_lock_tables
      since to truncate a MERGE table, we must open and lock
      merge children, and on those we don't have an MDL lock.
      Thus clear the ticket to satisfy MDL asserts.
    */
    table_ref->mdl_request.ticket= NULL;
  }

  /* Open the table as it will handle some required preparations. */
  if (open_and_lock_tables(thd, table_ref, FALSE, flags))
    DBUG_RETURN(TRUNCATE_FAILED_SKIP_BINLOG);

  /* Whether to truncate regardless of foreign keys. */
  if (! (thd->variables.option_bits & OPTION_NO_FOREIGN_KEY_CHECKS))
    if (fk_truncate_illegal_if_parent(thd, table_ref->table))
      DBUG_RETURN(TRUNCATE_FAILED_SKIP_BINLOG);

  error= table_ref->table->file->ha_truncate();
  if (unlikely(error))
  {
    table_ref->table->file->print_error(error, MYF(0));
    /*
      If truncate method is not implemented then we don't binlog the
      statement. If truncation has failed in a transactional engine then also
      we don't binlog the statment. Only in non transactional engine we binlog
      inspite of errors.
     */
    if (error == HA_ERR_WRONG_COMMAND ||
        table_ref->table->file->has_transactions())
      DBUG_RETURN(TRUNCATE_FAILED_SKIP_BINLOG);
    else
      DBUG_RETURN(TRUNCATE_FAILED_BUT_BINLOG);
  }
  DBUG_RETURN(TRUNCATE_OK);
}


/*
  Handle locking a base table for truncate.

  @param[in]  thd               Thread context.
  @param[in]  table_ref         Table list element for the table to
                                be truncated.
  @param[out] hton_can_recreate Set to TRUE if table can be dropped
                                and recreated.

  @retval  FALSE  Success.
  @retval  TRUE   Error.
*/

bool Sql_cmd_truncate_table::lock_table(THD *thd, TABLE_LIST *table_ref,
                                        bool *hton_can_recreate)
{
  TABLE *table= NULL;
  DBUG_ENTER("Sql_cmd_truncate_table::lock_table");

  /* Lock types are set in the parser. */
  DBUG_ASSERT(table_ref->lock_type == TL_WRITE);
  /* The handler truncate protocol dictates a exclusive lock. */
  DBUG_ASSERT(table_ref->mdl_request.type == MDL_EXCLUSIVE);

  /*
    Before doing anything else, acquire a metadata lock on the table,
    or ensure we have one.  We don't use open_and_lock_tables()
    right away because we want to be able to truncate (and recreate)
    corrupted tables, those that we can't fully open.

    MySQL manual documents that TRUNCATE can be used to repair a
    damaged table, i.e. a table that can not be fully "opened".
    In particular MySQL manual says: As long as the table format
    file tbl_name.frm is valid, the table can be re-created as
    an empty table with TRUNCATE TABLE, even if the data or index
    files have become corrupted.
  */
  if (thd->locked_tables_mode)
  {
    if (!(table= find_table_for_mdl_upgrade(thd, table_ref->db.str,
                                            table_ref->table_name.str, NULL)))
      DBUG_RETURN(TRUE);

    *hton_can_recreate= ha_check_storage_engine_flag(table->file->ht,
                                                     HTON_CAN_RECREATE);
    table_ref->mdl_request.ticket= table->mdl_ticket;
  }
  else
  {
    handlerton *hton;
    bool is_sequence;

    /* Acquire an exclusive lock. */
    DBUG_ASSERT(table_ref->next_global == NULL);
    if (lock_table_names(thd, table_ref, NULL,
                         thd->variables.lock_wait_timeout, 0))
      DBUG_RETURN(TRUE);

    if (!ha_table_exists(thd, &table_ref->db, &table_ref->table_name,
                         &hton, &is_sequence) ||
        hton == view_pseudo_hton)
    {
      my_error(ER_NO_SUCH_TABLE, MYF(0), table_ref->db.str,
               table_ref->table_name.str);
      DBUG_RETURN(TRUE);
    }

    if (!hton)
    {
      /*
        The table exists, but its storage engine is unknown, perhaps not
        loaded at the moment. We need to open and parse the frm to know the
        storage engine in question, so let's proceed with the truncation and
        try to open the table. This will produce the correct error message
        about unknown engine.
      */
      *hton_can_recreate= false;
    }
    else
      *hton_can_recreate= !is_sequence && hton->flags & HTON_CAN_RECREATE;
  }

  /*
    A storage engine can recreate or truncate the table only if there
    are no references to it from anywhere, i.e. no cached TABLE in the
    table cache.
  */
  if (thd->locked_tables_mode)
  {
    DEBUG_SYNC(thd, "upgrade_lock_for_truncate");
    /* To remove the table from the cache we need an exclusive lock. */
    if (wait_while_table_is_used(thd, table,
          *hton_can_recreate ? HA_EXTRA_PREPARE_FOR_DROP : HA_EXTRA_NOT_USED))
      DBUG_RETURN(TRUE);
    m_ticket_downgrade= table->mdl_ticket;
    /* Close if table is going to be recreated. */
    if (*hton_can_recreate)
      close_all_tables_for_name(thd, table->s, HA_EXTRA_NOT_USED, NULL);
  }
  else
  {
    /* Table is already locked exclusively. Remove cached instances. */
    tdc_remove_table(thd, TDC_RT_REMOVE_ALL, table_ref->db.str,
                     table_ref->table_name.str, FALSE);
  }

  DBUG_RETURN(FALSE);
}


/*
  Optimized delete of all rows by doing a full generate of the table.

  @remark Will work even if the .MYI and .MYD files are destroyed.
          In other words, it works as long as the .FRM is intact and
          the engine supports re-create.

  @param  thd         Thread context.
  @param  table_ref   Table list element for the table to be truncated.

  @retval  FALSE  Success.
  @retval  TRUE   Error.
*/

bool Sql_cmd_truncate_table::truncate_table(THD *thd, TABLE_LIST *table_ref)
{
  int error;
  bool binlog_stmt;
  DBUG_ENTER("Sql_cmd_truncate_table::truncate_table");

  DBUG_ASSERT((!table_ref->table) ||
              (table_ref->table && table_ref->table->s));

  /* Initialize, or reinitialize in case of reexecution (SP). */
  m_ticket_downgrade= NULL;

  /* If it is a temporary table, no need to take locks. */
  if (is_temporary_table(table_ref))
  {
    /* In RBR, the statement is not binlogged if the table is temporary. */
    binlog_stmt= !thd->is_current_stmt_binlog_format_row();

    thd->close_unused_temporary_table_instances(table_ref);

    error= handler_truncate(thd, table_ref, TRUE);

    /*
      No need to invalidate the query cache, queries with temporary
      tables are not in the cache. No need to write to the binary
      log a failed row-by-row delete even if under RBR as the table
      might not exist on the slave.
    */
  }
  else /* It's not a temporary table. */
  {
    bool hton_can_recreate;

    if (WSREP(thd) &&
        wsrep_to_isolation_begin(thd, table_ref->db.str, table_ref->table_name.str, 0))
        DBUG_RETURN(TRUE);
    if (lock_table(thd, table_ref, &hton_can_recreate))
      DBUG_RETURN(TRUE);

    if (hton_can_recreate)
    {
     /*
        The storage engine can truncate the table by creating an
        empty table with the same structure.
      */
      error= dd_recreate_table(thd, table_ref->db.str, table_ref->table_name.str);

      if (thd->locked_tables_mode && thd->locked_tables_list.reopen_tables(thd, false))
      {
        thd->locked_tables_list.unlink_all_closed_tables(thd, NULL, 0);
        error=1;
      }

      /* No need to binlog a failed truncate-by-recreate. */
      binlog_stmt= !error;
    }
    else
    {
      /*
        The engine does not support truncate-by-recreate.
        Attempt to use the handler truncate method.
      */
      error= handler_truncate(thd, table_ref, FALSE);

      /*
        All effects of a TRUNCATE TABLE operation are committed even if
        truncation fails in the case of non transactional tables. Thus, the
        query must be written to the binary log. The only exception is a
        unimplemented truncate method.
      */
      if (unlikely(error == TRUNCATE_OK || error == TRUNCATE_FAILED_BUT_BINLOG))
        binlog_stmt= true;
      else
        binlog_stmt= false;
    }

    /*
      If we tried to open a MERGE table and failed due to problems with the
      children tables, the table will have been closed and table_ref->table
      will be invalid. Reset the pointer here in any case as
      query_cache_invalidate does not need a valid TABLE object.
    */
    table_ref->table= NULL;
    query_cache_invalidate3(thd, table_ref, FALSE);
  }

  /* DDL is logged in statement format, regardless of binlog format. */
  if (binlog_stmt)
    error|= write_bin_log(thd, !error, thd->query(), thd->query_length());

  /*
    A locked table ticket was upgraded to a exclusive lock. After the
    the query has been written to the binary log, downgrade the lock
    to a shared one.
  */
  if (m_ticket_downgrade)
    m_ticket_downgrade->downgrade_lock(MDL_SHARED_NO_READ_WRITE);

  DBUG_RETURN(error);
}

/**
  Execute a TRUNCATE statement at runtime.

  @param  thd   The current thread.

  @return FALSE on success.
*/

bool Sql_cmd_truncate_table::execute(THD *thd)
{
  bool res= TRUE;
  TABLE_LIST *table= thd->lex->select_lex.table_list.first;
  DBUG_ENTER("Sql_cmd_truncate_table::execute");

  if (check_one_table_access(thd, DROP_ACL, table))
    DBUG_RETURN(res);

  if (! (res= truncate_table(thd, table)))
    my_ok(thd);

  DBUG_RETURN(res);
}