1. A method for performing an iceberg query, comprising: processing, by a computer processor, the iceberg query using a compressed bitmap index having a plurality of bitmap vectors in a database, wherein the iceberg query is a GROUP BY query operation on a set of grouping attributes with a selection condition; eliminating, by the computer processor, any of the plurality of bitmap vectors in the compressed bitmap index that fails to meet the selection condition thereby forming a result subset of the plurality of bitmap vectors, wherein the eliminating includes: reading a first subset of bitmap vectors from the plurality of bitmap vectors; ignoring each vector of the first subset in the plurality of bitmap vectors, which has a count of 1-bits below a predetermined threshold; reading a second subset of bitmap vectors from the plurality of bitmap vectors; ignoring each vector of the second subset in the plurality of bitmap vectors, which has a count of 1-bits below the predetermined threshold; and applying a bitwise And operation between all remaining bitmap vectors from the first subset and the second subset, wherein the bitwise And operation generating a nonempty result, thereby aligning the bitmap vectors in the result subset of according to respective positions of the remaining bitmap vectors in the first and second subsets, and a priority of the remaining bitmap vectors is defined by a position of a first untouched 1-bit in each of the remaining bitmap vectors, the first untouched 1-bit being a 1-bit with a smallest position in each of the remaining bitmap vectors.