Data storage in large databases is layered and chunked, with the table storage arranged into 'blocks'. Each block contains perhaps 1MB in each chunk{{efn-lr| PostgreSQL has a default block size of 128&multtimes; 8k pages, or 1MB.<ref name="Wahts new"/> Oracle terms these 'storage regions' and gives them a default size of 1MB.<ref>{{cite web|title=When is Exadata’s storage indexes used?|website=OakTable.net|url=http://www.oaktable.net/blog/when-exadata%E2%80%99s-storage-indexes-used?page=2}}</ref>}}<ref name="Richard Foote, 2012, I"/> and they are retrieved by requesting specific blocks from a disk-based storage layer. BRIN are a lightweight in-memory summary layer above this: each tuple in the index summarises one block as to the range of the data contained therein: its minimum and maximum values, and if the block contains any non-null data for the column(s) of interest.<ref name="Wong, 2015">{{Cite web
