Test file: 4,000,000 lines of “ab”, File Size is 16MB, tested on EmEditor v17.3.0 beta 1.

I have tried to increase the number in the Minimum File Size to Use Temporary File text box to 3,000 MB.
And also increase the number in the Memory Size text box to 26.

The result is the same, the first 9%(1,800,000 lines) is finished within 1 second, almost immediately.
but the rest of 91%(2,200,000 lines) spent more than 20 seconds.

In this simple test case, if use “Remove Newline Characters” command first, and then remove “b” character, will be finished quickly.
But it is not easy to handle complex replacement with Regexp for some real big files(200~400MB with 4,000,000~20,000,000 lines).
Therefore I will hope the “Replace” function still can optimize as “Remove Newline Characters” command.