1. A method, comprising: creating, by at least one processor, a bitmap identifying rows in an in-memory column-store database, the bitmap comprising a list of bit chunks, a bit chunk comprising an offset comprising a natural number indicating a chunk size, and a bit specification comprising one of an ordered row id list, a contiguous row id sequence, and a bit vector; modifying a row id of the bitmap; determining a bit specification of a bit chunk in the list of bit chunks; converting the bit specification of the bit chunk from a first type to a second type to reduce memory used to represent the bitmap, wherein the first type is different than the second type and the conversion is based on the determined bit specification and the modified row id; and performing database operations using the bitmap on the in-memory column-store database.