Author: Robert Sample
Posted: Wed Oct 05, 2016 3:22 pm (GMT 5.5)
The CISIZE for the INDEX should be large enough to hold pointers to all the DATA component CI in the CA -- anything larger is not going to make any difference. The rough rule of thumb is to take half the key length plus 4 (14 in this case) times the number of CI per CA in the DATA component (15 times 12 or 180 for 4096 CISIZE on 3390) or 2520 for the INDEX CISIZE. 2048 is probably too small, thinking some more about it (although I haven't seen any updated rule of thumb in some time; the key compression may now allow 2048 to work). Note that the INDEX CISIZE does not depend upon how the data is being read. The CISIZE for the DATA component should be small for random access and larger for sequential access -- but the system does use 4K for many things, so using a CISIZE smaller than 4K may increase overhead -- and it would definitely impact the INDEX CISIZE.
_________________
TANSTAAFL
The first rule of code reuse is that the code needs to be worth re-using.
"We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil." -- Donald Knuth
Posted: Wed Oct 05, 2016 3:22 pm (GMT 5.5)
The CISIZE for the INDEX should be large enough to hold pointers to all the DATA component CI in the CA -- anything larger is not going to make any difference. The rough rule of thumb is to take half the key length plus 4 (14 in this case) times the number of CI per CA in the DATA component (15 times 12 or 180 for 4096 CISIZE on 3390) or 2520 for the INDEX CISIZE. 2048 is probably too small, thinking some more about it (although I haven't seen any updated rule of thumb in some time; the key compression may now allow 2048 to work). Note that the INDEX CISIZE does not depend upon how the data is being read. The CISIZE for the DATA component should be small for random access and larger for sequential access -- but the system does use 4K for many things, so using a CISIZE smaller than 4K may increase overhead -- and it would definitely impact the INDEX CISIZE.
_________________
TANSTAAFL
The first rule of code reuse is that the code needs to be worth re-using.
"We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil." -- Donald Knuth