when the library cache area released

        Hi,

	Our customer uses oracle7.3 and X/open interfaces.
	There are many many tables. There are many many columns
	in tables. And there are many many resident sesssions. 
	
	I am anxious about the shared pool size, especially about
	library cache.

	The first question is,
	When is the library cache released ?

	I have tried some cases and the test results follows.
				
			hold_cursor=yes		hold_cursor=no

	prepare		allocate		allocate

	open cursor	allocate		allocate	

	close cursor	allocate		sometimes allocated but
						sometimes released !

	Is this spec of oracle7 or bug, or,,,,,
	Especially, I cannot understand that "sometomes allocated but
	sometimes released".

	My next question is,

	How much shared pool can be used for library cache.
	I tried some tests and I can't uses more than 60% of the shared
	pool for library cache.
		Is this spec ?
		The percentage of the usable shared pool for library cache
		is always 60% ? ( For example, many user requires dictionary
		cache, can we use 60% shared library for library cache ?)
		And When is the dictionary cache allocated and released ?