9. The system of claim 8 , wherein the operations further comprise: generating a word frequency distribution of frequencies of occurrences of words; assigning values to different numbers of merged words based on the word frequency distribution; and selecting one of the numbers of the merged words based on the assigned values, wherein the number of symbols comprises the selected number of the merged words, wherein each symbol maps to one of the merged words.
9. The system of claim 8 , wherein the operations further comprise: generating a word frequency distribution of frequencies of occurrences of words; assigning values to different numbers of merged words based on the word frequency distribution; and selecting one of the numbers of the merged words based on the assigned values, wherein the number of symbols comprises the selected number of the merged words, wherein each symbol maps to one of the merged words. 11. The system of claim 9 , wherein in the word frequency distribution of frequencies of occurrences of the words, words having a smaller length in bits are more frequently accessed than words having a larger length of bits.