Finding Eager Index Spools in the Plan Cache
Somewhere in your plan cache right now, there is probably a query quietly building an index every single time it runs. Not once. Every execution. It builds the index, uses it, and throws it away,…
What ROW and PAGE Compression Do to the Record
Data compression is one of the few storage features you can turn on with a single clause and measure the same afternoon. It changes the physical format of the record on the page, not the…
A Tour of SQL Server Page Types: Data, GAM, SGAM, PFS, IAM
Most of this storage series has been spent inside data pages, pulling rows apart byte by byte. But a data file is not only data pages. Scattered through it, at fixed and predictable spots, are…
Forwarded Records: What an UPDATE Can Do to a Heap
A heap, a table with no clustered index, has a failure mode that clustered tables do not: an UPDATE that makes a row larger can force it to physically move, and SQL Server leaves a…
Row-Overflow and LOB: When a Row Leaves the Page
A data page is 8 KB, and a single row is capped at 8,060 bytes of in-row data.[1] So what happens when you declare two varchar(5000) columns, or store a 20,000-character varchar(max), in a row…
How SQL Server Packs BIT Columns Into a Single Byte
A common worry about bit columns is that a table full of yes/no flags will waste a byte on every flag. It will not. SQL Server packs bit columns together, up to eight of them…