How to make users feel "stuttered" as little as possible in this case?

We need to make a Web-based reader, just like all the Web readers you use, such as turning pages left and right.
however, we have a bizarre need to calculate the total length of all content, or to search. This requires the implementation of a "content traversal" function. In addition, our content source is "iframe", not the data that has been parsed and given to us through ajax, but a real web address, each chapter is a web page! We need to control an iframe to load these pages in order, and then take the contents to calculate.

now there is a problem: when the covered iframe traverses and calculates, it will cause the page to stutter and change the response to the user"s operation.

excuse me, is there any way to optimize this? What are the optimization points to pay attention to?
Thank you

Mar.29,2021

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e8b691-1054.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e8b691-1054.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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