The following lines are from readme file present in the 
\src\backend\storage\lmgr folder of postgresql

"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."


I dont see any field called tupleId in LockTag..does it have another name?
Also, "(we currently never do this)"--> does this mean that we currently can 
acquire tuplelevel(row level) locks in postgresql?
Thank you
Jenny

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Sat, 26 Jul 2003 10:59:49 -0700
"Jenny -" <nat_lazy@hotmail.com>
granularity of locks in postgresql
On Sat, Jul 26, 2003 at 10:59:49AM -0700, Jenny - wrote:
> The following lines are from readme file present in the 
> \src\backend\storage\lmgr folder of postgresql
> 
> "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."

> I dont see any field called tupleId in LockTag..does it have another name?

I think the tupleId is actually represented by the pair
BlockNumber blkno, OffsetNumber offno

> Also, "(we currently never do this)"--> does this mean that we currently 
> can acquire tuplelevel(row level) locks in postgresql?

It should work, but think about memory requirements if you want to
acquire a lot of those.

-- 
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"Those who use electric razors are infidels destined to burn in hell while
we drink from rivers of beer, download free vids and mingle with naked
well shaved babes." (http://slashdot.org/comments.pl?sid=44793&cid=4647152)

Sat, 26 Jul 2003 14:50:15 -0400
Alvaro Herrera <alvherre@dcc.uchile.cl>
Re: granularity of locks in postgresql