On Sat, Mar 10, 2012 at 5:04 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Fri, Mar 9, 2012 at 2:34 PM, Robert Haas <robertmh...@gmail.com> wrote: >>> On Fri, Mar 9, 2012 at 2:26 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>>> Hm. I think "thousands" is an overestimate, but yeah the logic could be >>>> greatly simplified. However, I'm not sure we could avoid breaking the >>>> existing naming convention for WAL files. How much do we care about >>>> that? > >>> Probably not very much, since WAL files aren't portable across major >>> versions anyway. But I don't see why you couldn't keep the naming >>> convention - there's nothing to prevent you from converting a 64-bit >>> integer back into two 32-bit integers if and where needed. > >> On further reflection, this seems likely to break quite a few >> third-party tools. Maybe it'd be worth it anyway, but it definitely >> seems like it would be worth going to at least some minor trouble to >> avoid it. > > The main actual simplification would be in getting rid of the "hole" > at the end of each 4GB worth of WAL, cf this bit in xlog_internal.h: > > /* > * We break each logical log file (xlogid value) into segment files of the > * size indicated by XLOG_SEG_SIZE. 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) XLOG_SEG_SIZE) > #define XLogSegsPerFile (((uint32) 0xffffffff) / XLogSegSize) > #define XLogFileSize (XLogSegsPerFile * XLogSegSize) > > If we can't get rid of that and have a continuous 64-bit WAL address > space then it's unlikely we can actually simplify any logic. > > Now, doing that doesn't break the naming convention exactly; what it > changes is that there will be WAL files numbered xxxFFFF (for some > number of trailing-1-bits I'm too lazy to work out at the moment) where > before there were not. So the question really is how much external code > there is that is aware of that specific noncontiguous numbering behavior > and would be broken if things stopped being that way.
A page header contains WAL location, so getting rid of "hole" seems to break pg_upgrade. No? Unless pg_upgrade converts noncontinuous location to continuous one, we still need to handle noncontinuous one after upgrade. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
