>When i do reindexing in my application, I find the .cdx file is increased. This happens even if I do just reindexing, nothing else. Can any body help me in this?

Probably you are doing something like this:
. use abcd again in 0 exclusive
. index on field1 tag key1

In that case the CDX size will increase. You must do this:
. use abcd again in 0 exclusive
. pack
. reindex
. index on field1 tag key1

Joaquim