why this query fetching data very slow? it is cluster table konv

Dear Gents,

why this quer is fetching data very slow even though I have given it the primary keys I know that the Konv is Cluster Table but I have not face this problem before.

SELECT SINGLE kwert INTO jline-kwert FROM konv

WHERE knumh = '1002090527'

AND kposn = '000010' .