Re: Should walsernder check correctness of WAL records?

On Fri, Oct 02, 2020 at 12:16:25AM +0000, tsunakawa(dot)takay(at)fujitsu(dot)com wrote:
> IIUC, walsender tries hard to send WAL as fast as possible to reduce
> replication lag and transaction response time, so it doesn't try to
> peek each WAL record. I think it's good.

CRC calculation would unlikely be the bottleneck here, no? I would
assume that the extra lseek() calls needed to look after the record
data to be more harmful.

> In any case, the WAL can get corrupt during transmission, and
> writing and reading on the standby. So, the standby needs to check
> the WAL record CRC.

Yep. However, I would worry much more about the case of cold
archives. In my experience, there are higher risks to get a WAL
segment corrupted because it was on disk and that this disk got
corrupted. Transmission is a one-time short operation. Cold archives
could stay on disk for weeks before getting reused in WAL replay.
--
Michael