XML Data connection could not import a large amount of data

Hi Experts,

    I want to import some data into dashboard. Now there are 1,200 rows of data and it will increase to about 1600 in the future. But i found that the dashboard could only import 515 data at one time, so i decreased to 600 data and divided them into several parts. I use five XML Data connections rather than one. But When i clicked "Preview" button, the screen stayed in "Initializing" and nothing happend. It could not work effectively unless i reduce some of data.

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    I have two questions.

    1.Why i could not import some data into dashboard? Is that because of the connection I used or the capacity of the dashboard?

    2.How to solve this problem.

    THX.