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By Sprezz | Sunday, 21 June 2009 23:57 | 0 Comments
At one of our Canadian clients recently we were processing our way through a large file and without warning the AREV would crash and an NTDVM error would appear. This was a little annoying to say the least (this is what we British call understatement :)). As a rule of thumb, systems that don't crash the NTDVM are to be preferred.

We debugged this as much as we could in AREV but were getting nowhere. We could establish exactly where the crash occurred but it wasn't directly related to an i/o operation - as in it happened AFTER an i/o operation and not on the else clause

Eventually inspiration struck - we'd use OI to perform the same process and if it failed too we'd report a UD bug to Revelation, if it succeeded we'd report a terminal AREV bug to the client. With these two options in mind (A and B) we installed an evaluation copy of OI onto the server and reran the rest program using OI. Sure enough the program failed - but it failed cleanly with an FS error. An FS129 to be precise.

It was in this way that we discovered Option C. If at some point in the mists of time your client has gone directly to a network product that does not contain warnings about Group Calculation Error bugs and have thus never had the opportunity to fun FIXVOL.EXE or FIXGCE.EXE then they may still have tables out there containing this error. This would manifest itself by "losing" data and by occasionally abending the NTDVM. The solution is of course simple - run FIXVOL.EXE against the errant data.

To explain - when the 1.5 Network Service was introduced it came with an explanation that earlier versions of the Linear Hashing algorithm came with a bug in group calculation in tables having a modulo of greater than 64K. The documentation recommended using supplied programs to fix the problem tables.

We located a copy of said program on the Sprezz servers and were able to get back in business. It's at times like these that a long memory goes a long way to troubleshooting problems.

PS Revelation (as is comfortingly the case nowadays) when notified of this have moved to update the Service documentation AND provide download links for these utilities. Jolly good show!

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