On Mon, Jun 06, 2005 at 10:52:09AM -0500, John A Meinel wrote:
pg_xlog benefits from being super fast. Because it has to be fully
synced before the rest of the data can be committed. Yes they are small,
but if you can make it fast, you eliminate that overhead. It also
benefits from having it's own spindle, because you eliminate the seek
time. (Since it is always appending)
Eliminating the seeks is definately a win.
Anyway, my point is that pg_xlog isn't necessarily tiny. Many people
seem to set it as high as 100-200, and each one is 16MB.
It's not the size of the xlog, it's the size of the write. Unless you're
writing out a stripe size of data at once you're only effectively
writing to one disk pair at a time anyway. (Things change if you have a
big NVRAM cache to aggregate the writes, but you'd need a *lot* of
transaction activity to exceed the 50MB/s or so you could get from the
single raid1 pair in that scenario.)
Mike Stone
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