From: Vlad H. <hv...@us...> - 2007-01-04 20:59:24
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> > > These functions work with the disk controllers to ensure that > data/pages > > > are written in the best order. Further, all the writes occur in a > > > single system call, which would further increase IO performance. Are you talking about scatter\gather IO ? This is only API which can group several read\write operations in one OS call. It is introduced in NT specially for SQL Server and, iirc, present in Linux too. But it can group only consecutive operations - i.e. page numbers 1,2,3 can be read (or write) in single call but pages 1, 3 - can't. > > That's good for reads, but could wreck havoc on careful write. Exactly > I realized this was a problem, when the discussion about Overlapped IO > started 2 years ago and have been thinking on this... I also have in mind SUPERSEVER_V2 code. Perhaps we can reanimate it. At least prefetch logic. But looking at IB 7.x TPC-R results i was not impressed. So we must not blindly (re)implement it but also rethink it and improve when possible > I was thinking that all data of similar "priority/carefulness" could be > 'grouped' in one write call -- afterall, not all pages need to be > carefully written. > > Thoughts? Afraid i don't understand what do you mean under "'grouped' in one write call". Can you explain, please ? Regards, Vlad |