Re: CRCs (was Re: [GENERAL] Re: Loading optimization)

> > No, I thought we agreed disk block CRC was way overkill. If the CRC on
> > the WAL log checks for errors that are not checked anywhere else, then
> > fine, but I thought disk CRC would just duplicate the I/O subsystem/disk
> > checks.
>
> A disk-block CRC would detect partially written blocks (ie, power drops
> after disk has written M of the N sectors in a block). The disk's own
> checks will NOT consider this condition a failure. I'm not convinced
> that WAL will reliably detect it either (Vadim?). Certainly WAL will

Idea proposed by Andreas about "physical log" is implemented!
Now WAL saves whole data blocks on first after checkpoint
modification. This way on recovery modified data blocks will be
first restored *as a whole*. Isn't it much better than just
detection of partially writes?

Only one type of modification isn't covered at the moment -
updated t_infomask of heap tuples.

> not help for corruption caused by external agents, away from any updates
> that are actually being performed/logged.

What do you mean by "external agents"?

Vadim