Re: Further open item (Was: Status of 7.2)

> We are always willing to discuss changes that improve performance,
> reliability, standards compliance, etc.  However, "MS SQL does it, and MS
> SQL is fast" is not sufficient proof that a feature would improve average
> performance in PostgreSQL.  This issue has been brought up with similarly
> unsatisfactory arguments in the past, so you should be able to find out
> about the discussion in the archives.  Some of the arguments against this
> change were bigger indexes, slower write operations, non-existent proof
> that it's really faster, putting the index on a different disk will mostly
> obsolete the issue.  Consequently, this is currently not something that
> has got a chance to be implemented anytime soon.

I personally would like to have index scans that look up heap rows
record the heap expired status into the index entry via one bit of
storage.  This will not _prevent_ checking the heap but it will prevent
heap lookups for index entries that have been exipred for a long time. 
However, with the new vacuum, and perhaps autovacuum coming soon, may be
little need for this optimization.

The underlying problem the user is seeing is how to _know_ an index
tuple is valid without checking the heap, and I don't see how to do that
unless we start storing the transaction id in the index tuple, and that
requires extra storage.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
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