keep it fresh. keep it fun
Occasionally we do as we are told. And when Brent Ozar tells us that we should celebrate the first T-SQL Tuesday of 2017 by writing about SQL Server bugs and enhancement requests, the only appropriate response is “What color, sir?”
Continue reading “#TSQL2SDAY: Sing a song of unsigned ints”
While researching my previous post on latch promotion, I came across an odd piece of magic that made me do a double take. And sleep on it. And tear out my hair. I took it on faith that this is more likely a clever algorithm than a brain fart, but I could not stop asking myself repeatedly…
The piece of code in question is really simple, involving the maintenance of the BUF structure’s breferences member, which notionally is a count of how many times the page has been touched since the page’s counters were last reset.
Continue reading “How SQL Server counts page refs without counting”
Time to start chipping away at the monster subject of storage engine latches. If you’re anything like me, you were really impressed by the expositions of latches done by James Rowland-Jones (in Professional SQL Server 2008 Internals and Troubleshooting) and Bob Ward (PASS Summit “Inside Latches” session) when this information first started dribbling out. Now we have reached a point in history where latches seem to be used as a swear word. Well, for the record, I am still fascinated by them, and their internals are pretty darn marvellous.
Today I’m going to keep it comparatively focused, looking at nothing other than the Count member of the LatchBase class. Specifically, I’ll only be considering the act of acquiring an uncontended un-promoted latch, based on the SQL Server 2014 and 2016 latch implementation.
Continue reading “The Latch Files: Out for the count”
It’s not often that bit-twiddling and SQL sit well together. Different sides of the railway line and all that. However, I recently came across an interesting expression which fits the bill:
f(n) = ~n & ~(n-1)
Or in something closer to English:
f(n) = NOT n AND (NOT (n - 1))