Philip Warner wrote:
Andrew Dunstan wrote:
Unfortunately, it quite possibly would. You would not be able to build
two indexes on the same table in parallel, even though they wouldn't
have conflicting locks.
I suppose so, but:
1. By the same logic it might speed things up; it might build two
completely separate indexes and thereby avoid (some kind of) contention.
In any case, it would most likely do *something* else. It should only
reduce performance if (a) it can do nothing or (b) there is a benefit in
building multiple indexes on the same table at the same time.
2. Perhaps if there are a limited number of items that share
dependencies but which are known to be OK (ie. indexes), maybe list them
in the inner loop as exceptions and allow them to run parallel. This
would mean a failure to list a new TOC item type would result in worse
performance rather than a crash.
I will look at it in due course. Right now my concern is simply to get
something that works that we can do some testing with. I think that's
what we have now (fingers crossed). Some parts of it are jury rigged.
BTW, though, building indexes for the same table together is likely to
be a win AIUI, especially given the recent work on synchronised scans.
cheers
andrew
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