After looking at additional heap and b-tree index placed in pg_bitmapindex
namespace...
Additional heap contains unique values and page's number with offset number in
bitmap index, b-tree index contains tuples with the same values and ItemPointer
to heap's row. So, heap is an unnecessary step - b-tree index should store
ItemPointer to the bitmap index directly.
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Teodor Sigaev E-mail: teodor@sigaev.ru
WWW: http://www.sigaev.ru/