On Sun, 24 Jun 2007, Simon Riggs wrote:
I can't see why anyone would want to turn off smoothing: If they are doing many writes, then they will be effected by the sharp dive at checkpoint, which happens *every* checkpoint.
There are service-level agreement situations where a short and sharp disruption is more acceptable than a more prolonged one. As some of the overloaded I/O tests are starting to show, the LDC may be a backward step for someone in that sort of environment.
I am not a fan of introducing a replacement feature based on what I consider too limited testing, and I don't feel this one has been beat on long yet enough to start pruning features that would allow better backward compatibility/transitioning. I think that's introducing an unnecessary risk to the design.
We won't need to set checkpoint_segments so high, since performance is smoothed across checkpoints by LDC and its OK to allow them more frequently. So this concern need not apply with LDC.
Performance *should* be smoothed across by checkpoints by LDC and my concern *may* not apply. I think assuming it will always help based on the limited number of test results presented so far is extrapolation.
-- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
