On Sat, Jan 13, 2018 at 03:40:01PM +0000, Simon Riggs wrote: > The new two byte value is protected by CRC. The 2 byte value repeats > every 32768 WAL files. Any bit error in that value that made it appear > to be a current value would need to have a rare set of circumstances.
If you use the two lower bytes of the segment number, then this gets repeated every 64k segments, no? In terms of space this represents 500GB worth of WAL segments with a default segment size. Hence the more PostgreSQL scales, the more there is a risk of collision, and I am pretty sure that there are already deployments around allocating hundreds of gigs worth of space for the WAL partition. There are no problems of this class if using the 8-byte field xl_prev. It seems to me that we don't want to take any risks here. -- Michael
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