postgres Hot Heap Only Tuples - ghdrako/doc_snipets GitHub Wiki

• https://github.com/postgres/postgres/blob/master/src/backend/access/heap/README.HOT

Without HOT, every version of a row in an update chain has its own index entries, even if all indexed columns are the same. With HOT, a new tuple placed on the same page and with all indexed columns the same as its parent row version does not get new index entries. This means there is only one index entry for the entire update chain on the heap page. An index-entry-less tuple is marked with the HEAP_ONLY_TUPLE flag. The prior row version is marked HEAP_HOT_UPDATED, and (as always in an update chain) its t_ctid field links forward to the newer version.