EXPLAIN - Bitmap Or

Description:

Generate a bitmap of the union of two physical row location bitmaps (that is, locations that occur in either bitmap). The bitmaps can come from Bitmap Index Scans or other BitmapOr or BitmapAnd child nodes.

Note that, due to internal implementation limitations, BitmapOr nodes do not track the number of rows they produce. Their row count will always be listed as "Unknown" and they will not be flagged as mis-estimates.