Hi All,
I am having a suggestion for improving the filter queries which require
expression evaluation for
identifying its dictionary value.
*Current design *
In *greater than/less-than/Like* *filters*, system first iterates each row
present in the dictionary cache for identifying valid filter actual members
by applying the filter expression , once evaluation done system will hold
the list of identified valid filter actual member values(String), now in
next step again system will look up the dictionary cache in order to
identify the dictionary surrogate values of the identified members. this
look up is an additional cost to our system even though the look up
methodology is an binary search in dictionary cache.
*Proposed design/solution:*
*Identify the dictionary surrogate values in filter expression evaluation
step itself when actual dictionary values will be scanned for identifying
valid filter members .*
Keep a dictionary counter variable which will be increased when system
iterates through the dictionary cache in order to retrieve each actual
member stored in dictionary cache , after this system will evaluate each
row against the filter expression to identify whether its a valid filter
member or not, while doing this process itself counter value can be taken
as valid selected dictionary value since the actual member values and
its dictionary
values will be kept in same order in dictionary cache as the iteration
order.
*thus it will eliminate the further dictionary look up* *step *which is
required to retrieve the dictionary surrogate value against identified
actual valid filter member. this can also increase significantly the filter
query performance of such filter queries which require expression
evaluation to identify it the filter members by looking up dictionary
cache, like *greater than/less-than/Like* filters .
*Note : this optimization is applicable for dictionary columns.*
Please let me know for valid inputs/suggestions.
Thanks,
Sujith
