Re: Checkpoint cost, looks like it is WAL/CRC

Tom Lane wrote:
> Bruno Wolff III <bruno@wolff.to> writes:
> > Are you sure about that? That would probably be the normal case, but are
> > you promised that the hardware will write all of the sectors of a block
> > in order?
> 
> I don't think you can possibly assume that.  If the block crosses a
> cylinder boundary then it's certainly an unsafe assumption, and even
> within a cylinder (no seek required) I'm pretty sure that disk drives
> have understood "write the next sector that passes under the heads"
> for decades.

SCSI tagged queueing certainly allows 512-byte blocks to be reordered
during writes.

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