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Re: Why Index Lengh grow up
Posted by: Ingo Strüwing
Date: October 17, 2005 10:59AM

Sorry for the late reply. I was on vacation.

In mysys/tree.c I found:

in tree_insert():

uint alloc_size=sizeof(TREE_ELEMENT)+key_size+tree->size_of_element;
tree->allocated+=alloc_size;

and in tree_delete():

/* This doesn't include key_size, but better than nothing */
tree->allocated-= sizeof(TREE_ELEMENT)+tree->size_of_element;

The problem is that we do not know the key size in tree_delete(). I guess that the original author thought that the performance impact of a strlen() was not worth it for tables which were initially meant for short time life.

One can see this as a bug. If you like you can file a bug report on bugs.mysql.com.

Preliminarily you can workaround like so:

- If you sometimes have to delete *all* records, use TRUNCATE TABLE instead.
or
- Use an ALTER TABLE command which re-creates the table from time to time.

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