>After multiple runs on different blocksizes( a few anomalous results
>aside), I didn't see a whole lot of difference between
>FILE_FLAG_NO_BUFFERING being on or off for writing performance.
>However, with NO_BUFFERING set, the file is not *read* cached at all.
>While the performance is on not terrible for reads, some careful
>consideration would have to be given for using it outside of WAL. For
>WAL, though, it seems perfect. If my results are to be
>believed, we can
>expect up to a 30 yes, that's three + zero times faster sync
>performance
>by ditching FlushFileBuffers (although probably far less in practice).
>
Yes, for WAL it won't blow away read-cache stuff, since we normally
don't expect to read the data that's in WAL.
Is there actually a reason why we don't use O_DIRECT on Unix? From what
I can tell, O_SYNC does the write through but also puts it in the cache,
whereas O_DIRECT doesn't "waste cache" on it?
I was thinking of using O_DIRECT as the "compatibility flag" for the
combination of FILE_FLAG_WRITE_THROUGH and NO_BUFFERING, and using
O_SYNC for just the WRITE_THROUGH. Reasonable?
//Magnus
