Re: latch-free SCN scheme (10.1.0.3)

Hi,

> Now, if you're using private redolog strands, Oracle might use zero-copy
> mechanism for getting the contents from private strand to log buffer -
> using modern OS tricks such page loaning which manipulate with virtual
> memory mapping information - for example making the page read only and
> allowing it to be mapped somewhere into redolog buffer memory area, or
> completely switching virtual addresses of 2 physical memory ranges (pages)
> etc. This should reduce memory bus bandwidth usage and increase overall
> speed of these kind of memory "copy" operations if implemented properly.

Btw, this description of zero-copy redo is just my untested guess, based on few parameter names, latch statistics and background information. Even though operating systems do use such VM page remapping tricks for (like some TCP stack implementations) for performance reasons - Oracle might not do it - zero copy might also mean that redo records are directly constructed to private strand areas and written to disk directly from there by logwr, as opposed to creating these in PGA and copying to logbuffer then...

(to be continued...)

Tanel.

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