URGENT: Keyword Density Checker breaking on large text inputs, halting content optimization workflow!

the tool is designed to help users analyze long-form blog posts, articles, and landing page content, you know, for proper on-page seo. it works perfectly for shorter texts, anything under maybe ~3000 words. but anything substantial, like a 5000+ word article, just crashes it every single time.

when users paste in a large block of text, the tool either freezes indefinitely, returns a server timeout error, or just shows a generic '500 Internal Server Error'. it never completes the analysis, which means no keyword density or frequency report. it's infuriating for users trying to finish their content optimization tasks.

here's what i've tried so far:

• i've increased PHP memory_limit and max_execution_time significantly in php.ini, like to 512M and 300 seconds. no luck.
• checked server logs, and yeah, i'm seeing mostly memory exhaustion or script timeout errors. pretty clear what's happening, but not how to fix it efficiently.
• attempted to optimize the text processing logic, like using str_word_count more carefully, but it's really hard to debug when the whole script just crashes instead of giving a specific error.
• even tested different server configurations, tried more RAM, faster CPU, but the issue persists with large inputs. it's like the fundamental approach is wrong.
• verified network connectivity and client-side browser issues are not the cause, it's definitely server-side processing failing.

i expect it to process large texts, maybe taking a bit longer for huge articles, but still providing results. instead, it just fails entirely, which is useless for serious content optimization.

This is what I'm seeing in my logs when it crashes:

[2024-05-28 14:35:12] production.ERROR: Allowed memory size of 268435456 bytes exhausted (tried to allocate 12345678 bytes) in /var/www/html/app/Services/TextAnalyzer.php on line 123
[2024-05-28 14:35:12] production.INFO: User X attempted to analyze large content, resulted in memory error.

my specific questions are:

• what are the absolute best practices for handling extremely large string manipulations and calculations (like keyword frequency, n-grams, etc.) without exhausting server resources? i feel like there must be a smarter way.
• should i be offloading this to a background job queue, and if so, what's a good setup for a PHP/Laravel application that needs to process these kinds of heavy tasks? i'm thinking something like Redis and Horizon but i'm not sure where to start.
• are there specific libraries or algorithms optimized for this kind of text analysis that are super memory-efficient? maybe something in C/C++ that PHP can call?
• how do other popular SEO tools manage to process huge articles instantly without these issues? what's their secret sauce?

i'm completely stuck and this is a critical blocker for my users and our whole content optimization workflow. any expert advice would be a lifesaver. waiting for an expert reply.