Guru Guide To Sql Server Architecture And Internals.pdf ❲RECENT · 2025❳

Alex updated stats:

That open transaction was preventing the transaction log from truncating. The log had grown to 200 GB. The ETL’s large update inside FactSales_Load had to wait for log space, causing log autogrowth events (zero-initialization → slow). Guru Guide To Sql Server Architecture And Internals.pdf

The transaction log is a circular log. It can’t reuse space if any active transaction holds onto a VLFL (virtual log file) even if it’s old. Alex updated stats: That open transaction was preventing

Index stats were stale. The query optimizer thought the scan was cheaper because it didn’t know the table had grown massively since the last stats update. The transaction log is a circular log

SELECT * FROM sys.dm_os_buffer_descriptors WHERE database_id = DB_ID('SalesDB'); He saw that 40 GB of the buffer pool was filled with old data from a morning report. The ETL’s needed pages (the clustered index of Orders ) were being paged in from disk— couldn’t save it because the scan had already caused random I/O earlier.

The buffer pool is a shared resource. Morning report’s KEEP hints or large scans polluted the cache.

Alex killed the orphaned transaction (after confirming with the dev), shrunk the log safely, and set up alerting for long-running open transactions.