Re: Point in Time Recovery

On 7/6/2004 3:58 PM, Simon Riggs wrote:

> On Tue, 2004-07-06 at 08:38, Zeugswetter Andreas SB SD wrote:
>> > - by time - but the time stamp on each xlog record only specifies to the
>> > second, which could easily be 10 or more commits (we hope....)
>> >
>> > Should we use a different datatype than time_t for the commit timestamp,
>> > one that offers more fine grained differentiation between checkpoints?
>>
>> Imho seconds is really sufficient. If you know a more precise position
>> you will probably know it from backend log or an xlog sniffer. With those
>> you can easily use the TransactionId way.

TransactionID and timestamp is only sufficient if the transactions are
selected by their commit order. Especially in read committed mode,
consider this execution:

xid-1: start
xid-2: start
xid-2: update field x
xid-2: commit
xid-1: update field y
xid-1: commit

In this case, the update done by xid-1 depends on the row created by
xid-2. So logically xid-2 precedes xid-1, because it made its changes
earlier.

So you have to apply the log until you find the commit record of the
transaction you want apply last, and then stamp all transactions that
where in progress at that time as aborted.

Jan

>>
>
> OK, thanks. I'll just leave the time_t datatype just the way it is.
>
> Best Regards, Simon Riggs
>
>
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