On Monday 07 December 2009 21:44:37 Tom Lane wrote: > "Kevin Grittner" <kevin.gritt...@wicourts.gov> writes: > > Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> wrote: > >> In particular I wonder why we bother with the page headers. > > > > Since we re-use the file for a new segment, without overwriting the > > old contents, it seems like we would need to do *something* to > > reliably determine when we've hit the end of a segment and have > > moved into old data from a previous use of the file. Would your > > proposed changes cover that adequately? > AFAICT the proposal would make us 100% dependent on the record CRC > to detect when a record has been torn (ie, only the first few sectors > made it to disk). I'm a bit nervous about that from a reliability > standpoint --- with a 32-bit CRC you've got a 1-in-4-billion chance > of accepting bad data. Checking the page headers too gives us many > more bits that have to be as-expected to consider the data good. One could argue that thats a good argument to go back to 64bit CRCs. Considering that they are more seldomly computed with such a change and that CPUs got more modern...
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