following is taken from postgresql-7.3.2/src/backend/storage/lmgr/readme:

"If we are setting a table level lock
	both the blockId and tupleId (in an item pointer this is called
	the position) are set to invalid, if it is a page level lock the
	blockId is valid, while the tupleId is still invalid.  Finally if
	this is a tuple level lock (we currently never do this) then both
	the blockId and tupleId are set to valid specifications.  "

how do we check whether blockId and tupleId of LOCK.tag are valid or 
invalid?
is blockId same as tag.objId.blkno?  what field in LOCK.tag is tupleId?
thanks
jenny

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Thu, 07 Aug 2003 17:02:31 -0700
"Jenny -" <nat_lazy@hotmail.com>
LOCK.tag(figuring out granularity of lock)
"Jenny -" <nat_lazy@hotmail.com> writes:
> how do we check whether blockId and tupleId of LOCK.tag are valid or 
> invalid?

Look at how LockRelation and LockPage (in
src/backend/storage/lmgr/lmgr.c) set up the tags --- it might be clearer
then.

			regards, tom lane

Thu, 07 Aug 2003 20:19:06 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: LOCK.tag(figuring out granularity of lock) 