Simon Riggs wrote: > Transaction log files currently have timestamps, so that is > straightforward, but probably not the best we can do. We would > rollforward until the xlog file time > desired point in time. > > To make (2) work we would have to have a timestamp associated with each > transaction. This could be in one of two places: > 1. the transaction record in the clog > 2. the log record in the xlog > We would then recover the xlog record by record, until we found a record > that had a timestamp > desired point-in-time. > > Currently, neither of these places have a timestamp. Hmmmm. We can't use > pg_control because we are assuming that it needs recovery... > > I can't see any general way of adding a timestamp in any less than 2 > bytes. We don't need a timezone. The timestamp could refer to a number > of seconds since last checkpoint; since this is limited already by a GUC > to force checkpoints every so often. Although code avoids a checkpoint > if no updates have taken place, we wouldn't be too remiss to use a > forced checkpoint every 32,000 seconds (9 hours). > Assuming that accuracy of the point-in-time was of the order of > seconds?? If we went to 0.1 second accuracy, we could checkpoint (force) > every 40 minutes or so. All of that seems too restrictive. > If we went to milliseconds, then we could use a 4 byte value and use a > checkpoint (force) every 284 hours or 1.5 weeks. > Thoughts?
I was thinking --- how would someone know the time to use for restore? Certainly they will not know subsecond accuracy? Probably second-level accuracty is enough, _except_ when they want everything restored up to a DROP TABLE transaction or some major problem. Is there a way to give users a list of transactions on a log backup? Can we show them the username, database, or commands or something? Would they be able to restore up to a specific transaction in that case? Basically, we could give them sub-second recovery, but what value would it be? -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
