RE: unexpected heavy buffered IO during partition bitmap index rebuild
Date: Wed, 26 Sep 2012 16:59:51 -0500
Message-ID: <0EC8AF65BC8E9A4E9C4EB86F1882C96E04DA5A5F_at_ZBNAAEEX052.na.webmd.net>
| I'm confused. After a CTAS, you might still might have chaining, but I don't
| understand why there would be migration.
Whoops... more precisely stated (I hope)...
"In fact, after CTAS our new recreated segment (the target of the CTAS)
is 1/2 the size (in blocks) of the old segment which had 35% of its rows
that had been migrated (the source for the CTAS)."
...by which I was trying to compare the sizes of these two segments: the
"before CTAS" segment (when "slow" under bitmap index rebuild and doing
way--WAY!--more than the necessary amount of IO--even considering
migrated rows... 285 times the size of the segment) and the "after CTAS"
segment (when we had used CTAS to create a new replacement segment for
the partition which definitely made all migrated rows disappear and upon
which building a a bitmap index was nice and fast and incurred the
"expected" amount of IO--namely, reading a total amount of blocks which
appears to be the size of the segment).
-john
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