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Re: [HACKERS] pg_upgrade may be mortally wounded

From: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] pg_upgrade may be mortally wounded
Date: 1999-09-27 16:52:54
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Lists: pgsql-hackers
Tom, did we address this.  I forgot.

> Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> >> BTW, it seems to me that it is a good idea to kill and restart the
> >> postmaster immediately after pg_upgrade finishes.  Otherwise there might
> >> be buffers in shared memory that do not reflect the actual contents of
> >> the corresponding pages of the relation files (now that pg_upgrade
> >> overwrote the files with other data).
> > Your issue with buffer cache is a major one.  Clearly, this would be a
> > problem.   However, it is my understanding that the buffer cache after
> > initdb would only contain system table info, so if they pg_upgrade after
> > that, there is no way they have bad stuf in the cache, right?
> Cached copies of system tables obviously are no problem, since
> pg_upgrade doesn't overwrite those.  I'm concerned whether there can
> be cached copies of pages from user tables or indexes.  Since we've
> just done a bunch of CREATE INDEXes (and a VACUUM, if my latest hack
> is right), it seems at least possible that this would happen.
> Now all those user tables will be empty (zero-length files), so there is
> nothing to cache.  But the user indexes are *not* zero-length --- it looks
> like they are at least 2 pages long even when empty.  So there seems
> to be a real risk of having a cached copy of one of the pages of a user
> index while pg_upgrade is overwriting the index file with new data...
> 			regards, tom lane

  Bruce Momjian                        |
  maillist(at)candle(dot)pha(dot)pa(dot)us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

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