How to read all the rows from gridview when paging in enabled?

I am creating an web application to delete multiple records from gridview based on checkbox selection. I have maintained the checkbox selection using session/viewstate. But when i am trying to delete the selected multiple records, it is deleting the records only  from the currently selected page. e.g. if pagesize is 5 and i have 25 records. I selected record no. 2  and 3 from first page and 7,9 from second page etc. then on deleting it is deleting from the last selected page i.e. second page. How can i delete all the selected records from gridview?

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