有一种主键重复冲突叫自增字段溢出

 在大数据量的业务系统中，int的最大值为21亿，这个看似很大的数值，但在各种日志系统中，经常出现溢出的情况，不管是在应用程序中，还是在数据库中，一定需要注意类型超长的情况。 作为mysql的dba,能掌控的就是保证表的自增字段在将要溢出之前，提前通知研发人员该如何处理。 下面模拟一下数据库自增字段溢出之后的现象：

mysql> insert into  xcytest1 values(2147483645,1,'sd'); 
Query OK, 1 row affected (0.02 sec)

mysql> show create table  xcytest1;
+----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                                                                                            |
+----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| xcytest1 | CREATE TABLE "xcytest1" (
  "id" int(11) NOT NULL AUTO_INCREMENT,
  "age" int(11) DEFAULT NULL,
  "name" varchar(200) DEFAULT NULL,
  PRIMARY KEY ("id")
) ENGINE=InnoDB AUTO_INCREMENT=2147483646 DEFAULT CHARSET=utf8 |
+----------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> insert into  xcytest1(age,name) values(2,'asd');
Query OK, 1 row affected (0.02 sec)

mysql> insert into  xcytest1(age,name) values(2,'asd');
Query OK, 1 row affected (0.02 sec)

mysql> insert into  xcytest1(age,name) values(2,'asd');
ERROR 1062 (23000): Duplicate entry '2147483647' for key 'PRIMARY'

我们发现，当自增字段的自增值达到最大值，取下一个值的时候，还是取到了最大值，导致主键冲突报错。

为了提前发现这个现象，于是编写一个脚本，用来解析mysqldump导出的表结构的sql文件中关于自增字段的表的当前值是否快要溢出。

cat check_auto_incre.sh

sql_file_name=xcytest.sql
tmp_file_name=tmp.file.$$
out_put_file=out.file.sql
result_file=result.txt
warning_value=50
bigint_max=9223372036854775807
int_max=2147483647
unknown_result=unknow.autoinc.table.txt
cat /dev/null >$out_put_file
cat /dev/null >$result_file
cat /dev/null >$unknown_result
check_incr_value()
{

 local max_value=$1
 local cur_value=$2
 local table_name="${3}"
 local column_name="${4}"
 local column_type="${5}"
 used_pct=`expr $cur_value \* 100 `
 used_pct=`expr $used_pct / $max_value`
 if [ $used_pct -gt  $warning_value ] ; then 
      echo "warning_pct:${used_pct} currunt_value:${cur_value} ${column_type} ${table_name} ${column_name} " >>$result_file
 fi

}

while read   line_str  
do
   begin_str=`echo "${line_str}" |grep "^CREATE TABLE"  `
   if [ "X" == "X${begin_str}" ] ; then
        begin_strart=0
   else
        begin_start=1
        cat /dev/null >$tmp_file_name
   fi
   end_str=` echo $line_str |grep  "ENGINE="  `

   if [ "X" == "X${end_str}" ]; then
         char_end=0
   else
         char_end=1
   fi   
   echo $line_str  >>$tmp_file_name

   if [ $char_end  -eq   1 ]; then

       ifexistauto=`grep  "AUTO_INCREMENT" $tmp_file_name`

       if [ ! "X" == "X${ifexistauto}" ] ;then
             cat  $tmp_file_name  >>$out_put_file
             table_name=`grep "^CREATE TABLE"  $tmp_file_name|awk '{ print $3 }' `
             column_define=`grep "AUTO_INCREMENT," $tmp_file_name`
             column_name=`echo "$column_define" |awk '{print $1 } '` 
             column_type=`echo "$column_define" |awk '{print $2 } '`
             column_incre_value=`grep "AUTO_INCREMENT=" $tmp_file_name|awk '{ print $3} ' |awk -F"=" '{ print $2 } '`
             ## new create table , no AUTO_INCREMENT value ###
             if [ ! "X" == "X${column_incre_value}" ] ; then
               if [ "${column_type}" == "bigint(20)" ] ;then
                  check_incr_value $bigint_max  $column_incre_value  "${table_name}" "${column_name}" "${column_type}"
                  return_res=$?

               elif [ "${column_type}" == "int(11)" ];then 
                  
                  check_incr_value $int_max  $column_incre_value    "${table_name}" "${column_name}"  "${column_type}"
               else
                  cat $tmp_file_name  >>$unknown_result  
 
               fi
             else
                  cat $tmp_file_name  >>$unknown_result  
                     
             fi
             
       fi
       /bin/rm  $tmp_file_name

   fi

 
done < ${sql_file_name}

/bin/rm  $tmp_file_name
echo "#######check result #############"
cat  $result_file
if [ -s $unknown_result ] ;then  
  echo "unknow table "
  cat  $unknown_result 
fi

脚本的运行结果如下：

[mysql@MYSQLTMP ~]$ bash check_auto_incr.sh 
#######check result #############