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

Greg Stark <gsstark@mit.edu> writes:
> Tom Lane <tgl@sss.pgh.pa.us> writes:
>> What we *could* do is calculate a page-level CRC and
>> store it in the page header just before writing out.  Torn pages
>> would then manifest as a wrong CRC on read.  No correction ability,
>> but at least a reliable detection ability.

> At the same time as you do the CRC you can copy the bytes to a fresh page
> skipping the LSNs. Likewise, when writing out the page you have to calculate
> the CRC; at the same time as you calculate the CRC you write out the bytes to
> a temporary buffer adding LSNs and write that to disk.

Huh?  You seem to be proposing doing *both* things, which sounds entirely
pointless.

BTW, I was envisioning the page CRCs as something we'd only check during
crash recovery, not normal-operation reads.
        regards, tom lane