On Sat, 15 Jan 2005, Tom Lane wrote:
Alvaro Herrera <[EMAIL PROTECTED]> writes:Hackers, In access/heap/heapam.c, in heap_mark4update(), there's a comment that states
/* * XLOG stuff: no logging is required as long as we have no * savepoints. For savepoints private log could be used... */
Is this still true in light of 8.0's savepoints?
It isn't. Since mark4update is simply establishing a lock, which isn't going to be held across a system crash anyway, I see no need to WAL-log it. (But hmmm ... to support 2PC we'd probably need to do so ...)
Yes, for 2PC you need to keep all locks over system crash.
In any case I'm contemplating changing exclusive row locks to use LockAcquire, and supporting shared row locks using the same mechanism. All this per previous discussion on -hackers. We could get rid of heap_mark4update if that's done, right?
Right. The 2PC connection is another reason to do it that way --- 2PC would require some way to save locks anyhow, and it'd be nice if there were only one mechanism to deal with not two.
AFAICS, heap_mark4update calls XactLockTableWait for the updating transaction, and XactLockTableWait uses LockAcquire to do the waiting.
I must be missing something. Can someone briefly explain me what's special about this locking mechanism, please? How are you planning to change it?
- Heikki
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