Any chance you can work on save points/nested transactions? See doc/TODO.detail/transactions for info. I can help explaining the ideas in there.
--------------------------------------------------------------------------- Dhruv Pilania wrote: > Hi, > > I am a new postgresql developer. needed some help with wal/PITR. Can > someone working in this area answer my question? > (the email looks long but the question is simple :) ) > > I have been trying to implement undo of transactions using wal. i.e. given > a xid x, postgres can undo all operations of x. For starters, I > want to do this in very simple cases i.e. assume x only > inserts/updates/deletes tuples and does not change database schema. also I > assume that all of x's wal entries are in one segment. > > The code for this is quite simple if database supports undo or rollback to > a point in time. There is a lot of discussion on the mailing list about > PITR. I am eagerly waiting for the PITR code to be available on cvs. so > my questions are.... > > 1. once PITR has been implemented, infinite play forward will work. Will > undo also be supported? i.e. can we recover to the past from a "current" > wal log? > as a very simple scenario--- > xid 1 " insert record y in relation r" commit > xid 2 " update record x in relation r" commit > shutdown > ---now we take database back to start of xid 1. > > if answer to qn 1 is no... > 2. my approach is something like this, > scan log back until start of transaction record > scan forward until commit record > if record is for transaction x > undo(record) > to undo, > use preimage in record and everything else is pretty much same as redo. > i.e. we open relation, get desired block and work on it etc. > can someone tell me if this will work? > > > hoping someone currently working on wal/pitr can help me on this > issues.... > > thanks, > Dhruv > > > PS. > > transaction dependency tracking > ------------------------------- > I added support in postgres to do transaction dependency tracking. > basically, x depends on y if x reads something written by y. I maintain a > dependency graph and also a corresponding disk based log that is accessed > only at transaction commit. there is a tool which can be used to query > this graph. the time over heads are pretty low (< 1%). > with a dependency graph a DBA can say " I want to undo transaction x and > all transactions that depend on x". > > so now in the second phase, I am looking at undo of a transactions. any > thoughts on this are very welcome.... > > > -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026 ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
