Feb 13, 2008, 12:39 AM
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#8 (permalink)
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Hezbollah supporter
Join Date: Oct 2003
Location: Gefle, Sweden
Posts: 3,108
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Certainly. 
http://www.microsoft.com/technet/tec...l/default.aspx
Quote:
Windows 3.11 introduced "32-bit file access," which was a 32-bit implementation of the low-level file I/O interface. But the implementation of the Commit function contained a bug that effectively ignored requests to flush file buffers. If you took a program that flushed its file buffers and ran it on Windows 3.11, the flush call had no effect. As a result, if you lost power at just the wrong time, you ended up with a corrupted database.
The folks working on the Windows 95 file system fixed this bug, but new bug reports started to trickle in. Somebody’s accounts payable program started running really slowly. Then somebody else’s database program did the same. What was going on?
It turned out that these programs constantly issued flush calls. The programmers noticed that flush calls were really fast on Windows 3.11, so they sprinkled them liberally throughout their program. Write a byte, flush. Write a string, flush. Since the flushes were so fast, the app could commit the data to disk after every operation with no noticeable performance degradation. But once Windows 95 fixed the bug, these programs started to run very slowly since the Commit calls were suddenly doing actual work.
Of course, if the file system team had done nothing, these programs would have continued to run slowly and users would have jumped to the conclusion that Windows 95 was the problem. "Windows 95 runs like a dog," they would tell others. On the other hand, if the file system returned to the old Windows 3.11 behavior, they would have been reintroducing a bug that could lead to those pesky "file integrity problems."
So they concluded that the solution was to leave the bug fixed but add a check-box—albeit buried in the Troubleshooting page—to return to the Windows 3.11 behavior for those people who were running programs that encountered problems due to the bug being fixed.
It turned out that history repeated itself. In Windows ServerŪ 2003, the I/O folks found a bug where requests tagged as Forced Unit Access (FUA) would lose the FUA tag and be performed as normal I/O. It was the modern-day version of ignoring flush requests! They fixed the bug but left an option to return to the old buggy behavior. The Windows Server 2003 version of this checkbox is called "Enable Advanced Performance," but now you know it really just means "Restore old buggy behavior."
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Last edited by mkk; Feb 13, 2008 at 12:50 AM.
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