MySQL Forums :: Memory Storage Engine :: Why Index Lengh grow up

Hi,

I have use Heap table to store temp data. The data will be delete every minutes. I use the comment "show table status like 'mytbl'; The mysql version is 4.1.14
it show the following
Name mytbl
Engine HEAP
Version 9
Row_format Dynamic
Rows 1630
Avg_row_length 401
Data_length 4182720
Max_data_length 154020491
Index_length 806498309
Data_free 1654927
Auto_increment NULL
Create_time NULL
Update_time NULL
Check_time NULL
Collation latin1_swedish_ci
Checksum NULL
Create_options max_rows=3000000
Comment

The column of "Index_length" is continous to grow as the table is running insert, update and delete. Even the table is always empty the "Index_length" will not reset to a low value. Thus, it that normal?

Moreover, I have change the schema from changing the varchar column to char so that the "Row_format" is changed to "FIXED" when using show table status again. For this case, if the Index_length nearly the length of Max_data_length, the data give "Table Full" error even the table is total empty. Please advise what happen to that case??

Thanks for your help in advance.