Re: LyX 2.5.1: increasing memory usage and typing slowdown when copying/pasting equations

Hi,

Another data point: since updating my main copy of LyX to 2.5 on my Windows
machines, I see that LyX progressively becomes slower. The trigger is not
math editing or large documents, it seems to be my computer sleeping (and
it happens on other machines with a fresh LyX install with no LaTeX).
I'm not sure it's related, though. (Probably more a Qt thing?)

Thibaut Cuvelier


On Thu, 13 Aug 2026 at 18:49, Alessandro via lyx-devel <
[email protected]> wrote:

> Dear LyX developers,
>
> I would like to report a performance issue that I am experiencing with LyX
> 2.5.1 on Windows. I installed it a few days ago. I had been using LyX 2.4
> since 2025. I did not have any problem with LyX 2.4.
>
> The problem appears to be specifically related to editing, and especially *copying
> and pasting, mathematical equations*. When I work intensively on a
> math-heavy document, I notice that copying and pasting equations causes
> LyX's RAM consumption to increase. As I continue doing this, typing
> progressively becomes slower.
>
> I monitored LyX's memory usage in Windows Task Manager and observed the
> following pattern:
>
>
>    - Immediately after starting LyX: approximately 104–116 MB, with
>    typing perfectly responsive.
>    - After about 5 minutes of editing: approximately 135 MB.
>    - After additional editing: approximately 159 MB.
>    - After continued math editing, including copying and pasting
>    equations: approximately 331 MB, at which point typing becomes very slow.
>    - Closing and reopening the document without exiting LyX does not
>    solve the problem.
>    - Completely closing LyX and restarting it reduces memory usage back
>    to approximately 104 MB and immediately restores normal typing speed.
>
> In particular, I can see the RAM usage increasing as I copy and paste
> equations, and the deterioration in typing responsiveness appears to become
> more pronounced as memory usage increases.
>
> Overall system memory does not appear to be a constraint: total RAM usage
> is only around 44% when the problem occurs. Instant Preview is already
> disabled.
>
> I noticed a December 2025 discussion on the lyx-devel mailing list
> describing what appears to be a similar issue: progressively increasing
> memory consumption and typing slowdown during intensive equation editing,
> with performance restored after restarting LyX. In that discussion, Scott
> Kostyshak also mentioned having seen a similar report from a Windows user.
>
> I would be happy to perform additional tests to provide a reproducible
> example. Please let me know if there are particular diagnostics, debug
> logs, or tests that would be useful.
>
> Best regards,
>
> Alessandro
>
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