Re: WAL Log numbering

Attached is a patch that changes "sequential" to "ever-increasing".

> Justin Clift <justin(at)postgresql(dot)org> writes:
> > I would have though that after 00000000000000FE would be
> > 0000000000000100, not 0000000100000000.
>
> This is the intended behavior, I believe. The low-order half is a
> 32-bit byte offset DIV XLogSegSize --- we could compress out the zero
> bits, but only at the cost of wiring an assumption about XLogSegSize
> into the filename format. The reason that 0/FF is missing from the
> sequence is stated in xlog.h:
>
> /*
> * We break each logical log file (xlogid value) into 16Mb segments.
> * One possible segment at the end of each log file is wasted, to ensure
> * that we don't have problems representing last-byte-position-plus-1.
> */
> #define XLogSegSize ((uint32) (16*1024*1024))
> #define XLogSegsPerFile (((uint32) 0xffffffff) / XLogSegSize)
> #define XLogFileSize (XLogSegsPerFile * XLogSegSize)
>
> > Just checked through the Interactive docs (not sure which version of 7.1
> > they are) and says the numbers should be sequential.
>
> This would seem to be an oversimplification in the docs.
>
> regards, tom lane
>
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