255 column catalogue

This is a short list of articles discussing the problems (almost always) and oddities that appear when you define a table with more than 255 “real” columns. Odd details are always subject to change over time/version – so if it matters, test it and check it.

• 255 columns (May 2021) – make sure you count ALL the REAL columns
• Trouble-shooting (Aug 2019) – musings on problems due wide tables (based on seeing a suspect SQL update statement).
• 255 columns (Feb 2018) – huge increase in undo and redo with wide tables
• 255 columns (May 2017) – strange extremes in space usage with wide tables
• 255 columns (May 2017) – possible consequences of copying a wide table (with links to a couple of relevant articles on partition exchange and dropped columns.
• Migrated rows (May 2015) – diagnosing a “wide table”+”direct read” problem
• 255 columns (Feb 2015) – some side effects (with extras in the comments)
• How many row-pieces (Mar 2012) – What’s the worst case scenario for a table with more than 255 columns

Articles from other authors:

• Sayan Malakshinov, Feb 2017: intra-block chaining
• Sayan Malakshiniv, June 2017: 12.2 optimization of intra-block chaining