Bug#14521864: MYSQL 5.1 TO 5.5 BUGS PARTITIONING

Due to an internal change in the server code in between 5.1 and 5.5
(wl#2649) the hash function used in KEY partitioning changed
for numeric and date/time columns (from binary hash calculation
to character based hash calculation).

Also enum/set changed from latin1 ci based hash calculation to
binary hash between 5.1 and 5.5. (bug#11759782).

These changes makes KEY [sub]partitioned tables on any of
the affected column types incompatible with 5.5 and above,
since the calculation of partition id differs.

Also since InnoDB asserts that a deleted row was previously
read (positioned), the server asserts on delete of a row that
is in the wrong partition.

The solution for this situation is:

1) The partitioning engine will check that delete/update will go to the
partition the row was read from and give an error otherwise, consisting
of the rows partitioning fields. This will avoid asserts in InnoDB and
also alert the user that there is a misplaced row. A detailed error
message will be given, including an entry to the error log consisting
of both table name, partition and row content (PK if exists, otherwise
all partitioning columns).


2) A new optional syntax for KEY () partitioning in 5.5 is allowed:
[SUB]PARTITION BY KEY [ALGORITHM = N] (list_of_cols)
Where N = 1 uses the same hashing as 5.1 (Numeric/date/time fields uses
binary hashing, ENUM/SET uses charset hashing) N = 2 uses the same
hashing as 5.5 (Numeric/date/time fields uses charset hashing,
ENUM/SET uses binary hashing). If not set on CREATE/ALTER it will
default to 2.

This new syntax should probably be ignored by NDB.


3) Since there is a demand for avoiding scanning through the full
table, during upgrade the ALTER TABLE t PARTITION BY ... command is
considered a no-op (only .frm change) if everything except ALGORITHM
is the same and ALGORITHM was not set before, which allows manually
upgrading such table by something like:
ALTER TABLE t PARTITION BY KEY ALGORITHM = 1 () or
ALTER TABLE t PARTITION BY KEY ALGORITHM = 2 ()


4) Enhanced partitioning with CHECK/REPAIR to also check for/repair
misplaced rows. (Also works for ALTER TABLE t CHECK/REPAIR PARTITION)

CHECK FOR UPGRADE:
If the .frm version is < 5.5.3
and uses KEY [sub]partitioning
and an affected column type
then it will fail with an message:
KEY () partitioning changed, please run:
ALTER TABLE `test`.`t1`  PARTITION BY KEY ALGORITHM = 1 (a)
PARTITIONS 12
(i.e. current partitioning clause, with the addition of
ALGORITHM = 1)

CHECK without FOR UPGRADE:
if MEDIUM (default) or EXTENDED options are given:
Scan all rows and verify that it is in the correct partition.
Fail for the first misplaced row.

REPAIR:
if default or EXTENDED (i.e. not QUICK/USE_FRM):
Scan all rows and every misplaced row is moved into its correct
partitions.


5) Updated mysqlcheck (called by mysql_upgrade) to handle the
new output from CHECK FOR UPGRADE, to run the ALTER statement
instead of running REPAIR.

This will allow mysql_upgrade (or CHECK TABLE t FOR UPGRADE) to upgrade
a KEY [sub]partitioned table that has any affected field type
and a .frm version < 5.5.3 to ALGORITHM = 1 without rebuild.


Also notice that if the .frm has a version of >= 5.5.3 and ALGORITHM
is not set, it is not possible to know if it consists of rows from
5.1 or 5.5! In these cases I suggest that the user does:
(optional)
LOCK TABLE t WRITE;
SHOW CREATE TABLE t;
(verify that it has no ALGORITHM = N, and to be safe, I would suggest
backing up the .frm file, to be used if one need to change to another
ALGORITHM = N, without needing to rebuild/repair)
ALTER TABLE t <old partitioning clause, but with ALGORITHM = N>;
which should set the ALGORITHM to N (if the table has rows from
5.1 I would suggest N = 1, otherwise N = 2)
CHECK TABLE t;
(here one could use the backed up .frm instead and change to a new N
and run CHECK again and see if it passes)
and if there are misplaced rows:
REPAIR TABLE t;
(optional)
UNLOCK TABLES;

1 files changed, 463 insertions, 20 deletions

diff --git a/sql/ha_partition.cc b/sql/ha_partition.cc
index 6e1b3fc37b8..4afae052b76 100644
--- a/sql/ha_partition.cc
+++ b/sql/ha_partition.cc
@@ -1,5 +1,5 @@
 /*
-  Copyright (c) 2005, 2012, Oracle and/or its affiliates. All rights reserved.
+  Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 
   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
@@ -62,6 +62,8 @@
 #include "key.h"
 #include "sql_plugin.h"
 #include "table.h"                           /* HA_DATA_PARTITION */
+#include "sql_show.h"                        // append_identifier
+#include "sql_admin.h"                       // SQL_ADMIN_MSG_TEXT_SIZE
 
 #include "debug_sync.h"
 
@@ -271,6 +273,7 @@ void ha_partition::init_handler_variables()
   m_rec_length= 0;
   m_last_part= 0;
   m_rec0= 0;
+  m_err_rec= NULL;
   m_curr_key_info[0]= NULL;
   m_curr_key_info[1]= NULL;
   m_part_func_monotonicity_info= NON_MONOTONIC;
@@ -1035,10 +1038,11 @@ int ha_partition::preload_keys(THD *thd, HA_CHECK_OPT *check_opt)
     0                         Success
 */
 
-static int handle_opt_part(THD *thd, HA_CHECK_OPT *check_opt,
-                           handler *file, uint flag)
+int ha_partition::handle_opt_part(THD *thd, HA_CHECK_OPT *check_opt,
+                                  uint part_id, uint flag)
 {
   int error;
+  handler *file= m_file[part_id];
   DBUG_ENTER("handle_opt_part");
   DBUG_PRINT("enter", ("flag = %u", flag));
 
@@ -1047,9 +1051,27 @@ static int handle_opt_part(THD *thd, HA_CHECK_OPT *check_opt,
   else if (flag == ANALYZE_PARTS)
     error= file->ha_analyze(thd, check_opt);
   else if (flag == CHECK_PARTS)
+  {
     error= file->ha_check(thd, check_opt);
+    if (!error ||
+        error == HA_ADMIN_ALREADY_DONE ||
+        error == HA_ADMIN_NOT_IMPLEMENTED)
+    {
+      if (check_opt->flags & (T_MEDIUM | T_EXTEND))
+        error= check_misplaced_rows(part_id, false);
+    }
+  }
   else if (flag == REPAIR_PARTS)
+  {
     error= file->ha_repair(thd, check_opt);
+    if (!error ||
+        error == HA_ADMIN_ALREADY_DONE ||
+        error == HA_ADMIN_NOT_IMPLEMENTED)
+    {
+      if (check_opt->flags & (T_MEDIUM | T_EXTEND))
+        error= check_misplaced_rows(part_id, true);
+    }
+  }
   else if (flag == ASSIGN_KEYCACHE_PARTS)
     error= file->assign_to_keycache(thd, check_opt);
   else if (flag == PRELOAD_KEYS_PARTS)
@@ -1168,7 +1190,7 @@ int ha_partition::handle_opt_partitions(THD *thd, HA_CHECK_OPT *check_opt,
           part= i * num_subparts + j;
           DBUG_PRINT("info", ("Optimize subpartition %u (%s)",
                      part, sub_elem->partition_name));
-          if ((error= handle_opt_part(thd, check_opt, m_file[part], flag)))
+          if ((error= handle_opt_part(thd, check_opt, part, flag)))
           {
             /* print a line which partition the error belongs to */
             if (error != HA_ADMIN_NOT_IMPLEMENTED &&
@@ -1194,7 +1216,7 @@ int ha_partition::handle_opt_partitions(THD *thd, HA_CHECK_OPT *check_opt,
       {
         DBUG_PRINT("info", ("Optimize partition %u (%s)", i,
                             part_elem->partition_name));
-        if ((error= handle_opt_part(thd, check_opt, m_file[i], flag)))
+        if ((error= handle_opt_part(thd, check_opt, i, flag)))
         {
           /* print a line which partition the error belongs to */
           if (error != HA_ADMIN_NOT_IMPLEMENTED &&
@@ -3368,7 +3390,7 @@ exit:
 
     Called from sql_select.cc, sql_acl.cc, sql_update.cc, and sql_insert.cc.
     new_data is always record[0]
-    old_data is normally record[1] but may be anything
+    old_data is always record[1]
 */
 
 int ha_partition::update_row(const uchar *old_data, uchar *new_data)
@@ -3379,6 +3401,7 @@ int ha_partition::update_row(const uchar *old_data, uchar *new_data)
   longlong func_value;
   timestamp_auto_set_type orig_timestamp_type= table->timestamp_field_type;
   DBUG_ENTER("ha_partition::update_row");
+  m_err_rec= NULL;
 
   /*
     We need to set timestamp field once before we calculate
@@ -3396,6 +3419,25 @@ int ha_partition::update_row(const uchar *old_data, uchar *new_data)
     m_part_info->err_value= func_value;
     goto exit;
   }
+  /*
+    The protocol for updating a row is:
+    1) position the handler (cursor) on the row to be updated,
+       either through the last read row (rnd or index) or by rnd_pos.
+    2) call update_row with both old and new full records as arguments.
+
+    This means that m_last_part should already be set to actual partition
+    where the row was read from. And if that is not the same as the
+    calculated part_id we found a misplaced row, we return an error to
+    notify the user that something is broken in the row distribution
+    between partitions! Since we don't check all rows on read, we return an
+    error instead of correcting m_last_part, to make the user aware of the
+    problem!
+  */
+  if (old_part_id != m_last_part)
+  {
+    m_err_rec= old_data;
+    DBUG_RETURN(HA_ERR_NO_PARTITION_FOUND);
+  }
 
   m_last_part= new_part_id;
   start_part_bulk_insert(thd, new_part_id);
@@ -3501,12 +3543,34 @@ int ha_partition::delete_row(const uchar *buf)
   int error;
   THD *thd= ha_thd();
   DBUG_ENTER("ha_partition::delete_row");
+  m_err_rec= NULL;
 
   if ((error= get_part_for_delete(buf, m_rec0, m_part_info, &part_id)))
   {
     DBUG_RETURN(error);
   }
-  m_last_part= part_id;
+  /*
+    The protocol for deleting a row is:
+    1) position the handler (cursor) on the row to be deleted,
+       either through the last read row (rnd or index) or by rnd_pos.
+    2) call delete_row with the full record as argument.
+
+    This means that m_last_part should already be set to actual partition
+    where the row was read from. And if that is not the same as the
+    calculated part_id we found a misplaced row, we return an error to
+    notify the user that something is broken in the row distribution
+    between partitions! Since we don't check all rows on read, we return an
+    error instead of forwarding the delete to the correct (m_last_part)
+    partition!
+    TODO: change the assert in InnoDB into an error instead and make this one
+    an assert instead and remove the get_part_for_delete()!
+  */
+  if (part_id != m_last_part)
+  {
+    m_err_rec= buf;
+    DBUG_RETURN(HA_ERR_NO_PARTITION_FOUND);
+  }
+
   tmp_disable_binlog(thd);
   error= m_file[part_id]->ha_delete_row(buf);
   reenable_binlog(thd);
@@ -4347,7 +4411,6 @@ int ha_partition::index_init(uint inx, bool sorted)
   file= m_file;
   do
   {
-    /* TODO RONM: Change to index_init() when code is stable */
     if (bitmap_is_set(&(m_part_info->used_partitions), (file - m_file)))
       if ((error= (*file)->ha_index_init(inx, sorted)))
       {
@@ -6827,6 +6890,57 @@ enum row_type ha_partition::get_row_type() const
 }
 
 
+void ha_partition::append_row_to_str(String &str)
+{
+  Field **field_ptr;
+  const uchar *rec;
+  bool is_rec0= !m_err_rec || m_err_rec == table->record[0];
+  if (is_rec0)
+    rec= table->record[0];
+  else
+    rec= m_err_rec;
+  // If PK, use full PK instead of full part field array!
+  if (table->s->primary_key != MAX_KEY)
+  {
+    KEY *key= table->key_info + table->s->primary_key;
+    KEY_PART_INFO *key_part=     key->key_part;
+    KEY_PART_INFO *key_part_end= key_part + key->key_parts;
+    if (!is_rec0)
+      set_key_field_ptr(key, rec, table->record[0]);
+    for (; key_part != key_part_end; key_part++)
+    {
+      Field *field= key_part->field;
+      str.append(" ");
+      str.append(field->field_name);
+      str.append(":");
+      field_unpack(&str, field, rec, 0, false);
+    }
+    if (!is_rec0)
+      set_key_field_ptr(key, table->record[0], rec);
+  }
+  else
+  {
+    if (!is_rec0)
+      set_field_ptr(m_part_info->full_part_field_array, rec,
+                    table->record[0]);
+    /* No primary key, use full partition field array. */
+    for (field_ptr= m_part_info->full_part_field_array;
+         *field_ptr;
+         field_ptr++)
+    {
+      Field *field= *field_ptr;
+      str.append(" ");
+      str.append(field->field_name);
+      str.append(":");
+      field_unpack(&str, field, rec, 0, false);
+    }
+    if (!is_rec0)
+      set_field_ptr(m_part_info->full_part_field_array, table->record[0],
+                    rec);
+  }
+}
+
+
 void ha_partition::print_error(int error, myf errflag)
 {
   THD *thd= ha_thd();
@@ -6835,24 +6949,72 @@ void ha_partition::print_error(int error, myf errflag)
   /* Should probably look for my own errors first */
   DBUG_PRINT("enter", ("error: %d", error));
 
-  if ((error == HA_ERR_NO_PARTITION_FOUND) &&
-      ! (thd->lex->alter_info.flags & ALTER_TRUNCATE_PARTITION))
-    m_part_info->print_no_partition_found(table);
-  else
+  if (error == HA_ERR_NO_PARTITION_FOUND)
   {
-    /* In case m_file has not been initialized, like in bug#42438 */
-    if (m_file)
+    switch(thd_sql_command(thd))
     {
-      if (m_last_part >= m_tot_parts)
+    case SQLCOM_DELETE:
+    case SQLCOM_DELETE_MULTI:
+    case SQLCOM_UPDATE:
+    case SQLCOM_UPDATE_MULTI:
+      if (m_err_rec)
+      {
+        uint max_length;
+        char buf[MAX_KEY_LENGTH];
+        const char *msg= "Found a row in wrong partition (";
+        String str(buf,sizeof(buf),system_charset_info);
+        uint32 part_id;
+        /* Should only happen on DELETE or UPDATE! */
+        str.length(0);
+        str.append_ulonglong(m_last_part);
+        str.append(" != ");
+        if (!get_part_for_delete(m_err_rec, m_rec0, m_part_info, &part_id))
+        {
+          str.append_ulonglong(part_id);
+        }
+        str.append(")");
+        append_row_to_str(str);
+        /* Log this error, so the DBA can notice it and fix it! */
+        sql_print_error("Table '%-192s' corrupted: %s%s\n"
+                        "Please CHECK and REPAIR the table!",
+                        table->s->table_name.str, msg, str.c_ptr_safe());
+
+        max_length= (MYSQL_ERRMSG_SIZE-
+                     (uint) strlen(msg));
+        if (str.length() >= max_length)
+        {
+          str.length(max_length-4);
+          str.append(STRING_WITH_LEN("..."));
+        }
+        my_printf_error(ER_NO_PARTITION_FOR_GIVEN_VALUE, "%s%s", MYF(0),
+                        msg, str.c_ptr_safe());
+        m_err_rec= NULL;
+        DBUG_VOID_RETURN;
+      }
+    default:
       {
-        DBUG_ASSERT(0);
-        m_last_part= 0;
+        if (!(thd->lex->alter_info.flags & ALTER_TRUNCATE_PARTITION))
+        {
+          m_part_info->print_no_partition_found(table);
+          DBUG_VOID_RETURN;
+        }
       }
-      m_file[m_last_part]->print_error(error, errflag);
+      /* fall through to generic error handling. */
     }
-    else
-      handler::print_error(error, errflag);
   }
+
+  /* In case m_file has not been initialized, like in bug#42438 */
+  if (m_file)
+  {
+    if (m_last_part >= m_tot_parts)
+    {
+      DBUG_ASSERT(0);
+      m_last_part= 0;
+    }
+    m_file[m_last_part]->print_error(error, errflag);
+  }
+  else
+    handler::print_error(error, errflag);
   DBUG_VOID_RETURN;
 }
 
@@ -7561,6 +7723,287 @@ int ha_partition::indexes_are_disabled(void)
 }
 
 
+/**
+  Check/fix misplaced rows.
+
+  @param read_part_id  Partition to check/fix.
+  @param repair        If true, move misplaced rows to correct partition.
+
+  @return Operation status.
+    @retval 0     Success
+    @retval != 0  Error
+*/
+
+int ha_partition::check_misplaced_rows(uint read_part_id, bool repair)
+{
+  int result= 0;
+  uint32 correct_part_id;
+  longlong func_value;
+  longlong num_misplaced_rows= 0;
+
+  DBUG_ENTER("ha_partition::check_misplaced_rows");
+
+  DBUG_ASSERT(m_file);
+
+  if (repair)
+  {
+    /* We must read the full row, if we need to move it! */
+    bitmap_set_all(table->read_set);
+    bitmap_set_all(table->write_set);
+  }
+  else
+  {
+    /* Only need to read the partitioning fields. */
+    bitmap_union(table->read_set, &m_part_info->full_part_field_set);
+  }
+
+  if ((result= m_file[read_part_id]->ha_rnd_init(1)))
+    DBUG_RETURN(result);
+
+  while (true)
+  {
+    if ((result= m_file[read_part_id]->rnd_next(m_rec0)))
+    {
+      if (result == HA_ERR_RECORD_DELETED)
+        continue;
+      if (result != HA_ERR_END_OF_FILE)
+        break;
+
+      if (num_misplaced_rows > 0)
+      {
+        print_admin_msg(ha_thd(), "warning", table_share->db.str, table->alias,
+                        opt_op_name[REPAIR_PARTS],
+                        "Moved %lld misplaced rows",
+                        num_misplaced_rows);
+      }
+      /* End-of-file reached, all rows are now OK, reset result and break. */
+      result= 0;
+      break;
+    }
+
+    result= m_part_info->get_partition_id(m_part_info, &correct_part_id,
+                                          &func_value);
+    if (result)
+      break;
+
+    if (correct_part_id != read_part_id)
+    {
+      num_misplaced_rows++;
+      if (!repair)
+      {
+        /* Check. */
+        print_admin_msg(ha_thd(), "error", table_share->db.str, table->alias,
+                        opt_op_name[CHECK_PARTS],
+                        "Found a misplaced row");
+        /* Break on first misplaced row! */
+        result= HA_ADMIN_NEEDS_UPGRADE;
+        break;
+      }
+      else
+      {
+        DBUG_PRINT("info", ("Moving row from partition %d to %d",
+                            read_part_id, correct_part_id));
+
+        /*
+          Insert row into correct partition. Notice that there are no commit
+          for every N row, so the repair will be one large transaction!
+        */
+        if ((result= m_file[correct_part_id]->ha_write_row(m_rec0)))
+        {
+          /*
+            We have failed to insert a row, it might have been a duplicate!
+          */
+          char buf[MAX_KEY_LENGTH];
+          String str(buf,sizeof(buf),system_charset_info);
+          str.length(0);
+          if (result == HA_ERR_FOUND_DUPP_KEY)
+          {
+            str.append("Duplicate key found, "
+                       "please update or delete the record:\n");
+            result= HA_ADMIN_CORRUPT;
+          }
+          m_err_rec= NULL;
+          append_row_to_str(str);
+
+          /*
+            If the engine supports transactions, the failure will be
+            rollbacked.
+          */
+          if (!m_file[correct_part_id]->has_transactions())
+          {
+            /* Log this error, so the DBA can notice it and fix it! */
+            sql_print_error("Table '%-192s' failed to move/insert a row"
+                            " from part %d into part %d:\n%s",
+                            table->s->table_name.str,
+                            read_part_id,
+                            correct_part_id,
+                            str.c_ptr_safe());
+          }
+          print_admin_msg(ha_thd(), "error", table_share->db.str, table->alias,
+                          opt_op_name[REPAIR_PARTS],
+                          "Failed to move/insert a row"
+                          " from part %d into part %d:\n%s",
+                          read_part_id,
+                          correct_part_id,
+                          str.c_ptr_safe());
+          break;
+        }
+
+        /* Delete row from wrong partition. */
+        if ((result= m_file[read_part_id]->ha_delete_row(m_rec0)))
+        {
+          if (m_file[correct_part_id]->has_transactions())
+            break;
+          /*
+            We have introduced a duplicate, since we failed to remove it
+            from the wrong partition.
+          */
+          char buf[MAX_KEY_LENGTH];
+          String str(buf,sizeof(buf),system_charset_info);
+          str.length(0);
+          m_err_rec= NULL;
+          append_row_to_str(str);
+
+          /* Log this error, so the DBA can notice it and fix it! */
+          sql_print_error("Table '%-192s': Delete from part %d failed with"
+                          " error %d. But it was already inserted into"
+                          " part %d, when moving the misplaced row!"
+                          "\nPlease manually fix the duplicate row:\n%s",
+                          table->s->table_name.str,
+                          read_part_id,
+                          result,
+                          correct_part_id,
+                          str.c_ptr_safe());
+          break;
+        }
+      }
+    }
+  }
+
+  int tmp_result= m_file[read_part_id]->ha_rnd_end();
+  DBUG_RETURN(result ? result : tmp_result);
+}
+
+
+#define KEY_PARTITIONING_CHANGED_STR \
+  "KEY () partitioning changed, please run:\nALTER TABLE %s.%s %s"
+
+int ha_partition::check_for_upgrade(HA_CHECK_OPT *check_opt)
+{
+  int error= HA_ADMIN_NEEDS_CHECK;
+  DBUG_ENTER("ha_partition::check_for_upgrade");
+
+  /*
+    This is called even without FOR UPGRADE,
+    if the .frm version is lower than the current version.
+    In that case return that it needs checking!
+  */
+  if (!(check_opt->sql_flags & TT_FOR_UPGRADE))
+    DBUG_RETURN(error);
+
+  /*
+    Partitions will be checked for during their ha_check!
+
+    Check if KEY (sub)partitioning was used and any field's hash calculation
+    differs from 5.1, see bug#14521864.
+  */
+  if (table->s->mysql_version < 50503 &&              // 5.1 table (<5.5.3)
+      ((m_part_info->part_type == HASH_PARTITION &&   // KEY partitioned
+        m_part_info->list_of_part_fields) ||
+       (m_is_sub_partitioned &&                       // KEY subpartitioned
+        m_part_info->list_of_subpart_fields)))
+  {
+    Field **field;
+    if (m_is_sub_partitioned)
+    {
+      field= m_part_info->subpart_field_array;
+    }
+    else
+    {
+      field= m_part_info->part_field_array;
+    }
+    for (; *field; field++)
+    {
+      switch ((*field)->real_type()) {
+      case MYSQL_TYPE_TINY:
+      case MYSQL_TYPE_SHORT:
+      case MYSQL_TYPE_LONG:
+      case MYSQL_TYPE_FLOAT:
+      case MYSQL_TYPE_DOUBLE:
+      case MYSQL_TYPE_NEWDECIMAL:
+      case MYSQL_TYPE_TIMESTAMP:
+      case MYSQL_TYPE_LONGLONG:
+      case MYSQL_TYPE_INT24:
+      case MYSQL_TYPE_TIME:
+      case MYSQL_TYPE_DATETIME:
+      case MYSQL_TYPE_YEAR:
+      case MYSQL_TYPE_NEWDATE:
+      case MYSQL_TYPE_ENUM:
+      case MYSQL_TYPE_SET:
+        {
+          THD *thd= ha_thd();
+          char *part_buf;
+          String db_name, table_name;
+          uint part_buf_len;
+          bool skip_generation= false;
+          partition_info::enum_key_algorithm old_algorithm;
+          old_algorithm= m_part_info->key_algorithm;
+          error= HA_ADMIN_FAILED;
+          append_identifier(ha_thd(), &db_name, table_share->db.str,
+                            table_share->db.length);
+          append_identifier(ha_thd(), &table_name, table_share->table_name.str,
+                            table_share->table_name.length);
+          if (m_part_info->key_algorithm != partition_info::KEY_ALGORITHM_NONE)
+          {
+            /*
+              Only possible when someone tampered with .frm files,
+              like during tests :)
+            */
+            skip_generation= true;
+          }
+          m_part_info->key_algorithm= partition_info::KEY_ALGORITHM_51;
+          if (skip_generation ||
+              !(part_buf= generate_partition_syntax(m_part_info,
+                                                    &part_buf_len,
+                                                    true,
+                                                    true,
+                                                    NULL,
+                                                    NULL)) ||
+          /* Also check that the length is smaller than the output field! */
+              (part_buf_len + db_name.length() + table_name.length()) >=
+                (SQL_ADMIN_MSG_TEXT_SIZE -
+                  (strlen(KEY_PARTITIONING_CHANGED_STR) - 3)))
+          {
+            print_admin_msg(thd, "error", table_share->db.str, table->alias,
+                            opt_op_name[CHECK_PARTS],
+                            KEY_PARTITIONING_CHANGED_STR,
+                            db_name.c_ptr_safe(), table_name.c_ptr_safe(),
+                            "<old partition clause>, but add ALGORITHM = 1"
+                            " between 'KEY' and '(' to change the metadata"
+                            " without the need of a full table rebuild.");
+          }
+          else
+          {
+            print_admin_msg(thd, "error", table_share->db.str, table->alias,
+                            opt_op_name[CHECK_PARTS],
+                            KEY_PARTITIONING_CHANGED_STR,
+                            db_name.c_ptr_safe(), table_name.c_ptr_safe(),
+                            part_buf);
+          }
+          m_part_info->key_algorithm= old_algorithm;
+        }
+        break;
+      default:
+        /* Not affected! */
+        ;
+      }
+    }
+  }
+
+  DBUG_RETURN(error);
+}
+
+
 struct st_mysql_storage_engine partition_storage_engine=
 { MYSQL_HANDLERTON_INTERFACE_VERSION };