A rewrite, or a "rewrite"? I've seen plenty of press articles about something MS "rewrote" from the ground up, including windows itself, and they are never true.
Unless they actually started from a blank source repository then it was not a rewrite.
i was there, from 1995 on. It was a real rewrite. sybase's optimizer was the biggest piece of shit ever. losing predicates, functions that called each other multiple times to rewrite the tree. We didn't have docs on the page formats, we have to reverse engineer it. The only piece not completely rewritten in the first release in 7.0 shipping in 1998 was the tree/algebraizer that was the input to the query processor. it was so messy and horrible even our team of champions couldn't do it in the first release.
It would seem a lot of the protocol was kept though, no? IIRC there wasn't much diff between the mssql 6.5 protocol and mssql 7 protocol. I had been working with the freetds project in 1999/2000 and spent way too much time learning about some of that, although... it was 17 years ago and details are fading!
> sybase's optimizer was the biggest piece of shit ever
Sybase even in the 11.5 days was horrible. Even with updated stats, it would drop off the cliff and you would suddenly have queries that took less than a second go to multiple minutes. It was the database where I had to force a lot of indexes. It really got confused with simple reference tables. Temporary tables were just plain problematic unless you did the trick of declaring them in the outer procedure and then calling another stored procedure to actually use the temp table.
I suppose there may have been some old code in there to maintain backwards compatibility with e.g. the T-SQL parser, but it was C before and C++ after the "rewrite"...
I checked a few (https://en.wiktionary.org/wiki/rewrite) they all seem to indicate that it's writing something again. Some included revise as a synonym, but the parent said "complete rewrite" which would exclude that. Otherwise where is the cut off line? Can I rewrite 1% and call something a rewrite?
I never knew the definition of rewrite would be so controversial.
Don't down vote him. More often than not those are just normal refactoring with PR attempts to get rid of old license info. See IE7, it got rid of Mosaic license info yet even IE11 and early Edge contains web render code and mouse behaviors that can be traced back to Mosaic web browser, where it forked off. The same is with game engines, Valve's Source engine 2 started as a fork of ID's Quake 1 engine and it's still evident even in 2017. Or Dunia engine from Ubisoft traces back to FarCry 1 engine from Crytek. Or Call of Duty engine originates in Quake 3 engine from ID. Or in WinWord 2010 originates in WinWord2 code from 1990, with code that predates threads and uses fibers (known as coroutines nowadays in other languages).
I'm pretty skeptical that Edge ever contained any old Spyglass code. If they kept the licensing disclaimer in those early versions, I suspect it was because proving that none of the old code was there wasn't a priority for anyone.
And these can also be explained by unit tests .. you keep the old unit tests and rewrite everything so those tests pass. Sometimes that means getting some of the same weird quirks or gotchas, but hopefully refactored so they are all in one place and clearly documented.
Unless they actually started from a blank source repository then it was not a rewrite.