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Assigned Teams:

Query Execution
Backwards Compatibility:
Minor Change
Operating System:
ALL
Backport Requested:

v8.2, v8.0, v7.0
Steps To Reproduce:

Hide

Make a query with a regex pattern longer than 16384.

```js
const kMaxRegexPatternLen = 16384 + 1;
const patternMaxLen = "c".repeat(kMaxRegexPatternLen);
```

Run query:
```
{ fieldName: \{ "$regex": patternMaxLen}
}
```

Previously, this query ran fine with a limit upwards of 32764 characters.

Show
Make a query with a regex pattern longer than 16384. ```js const kMaxRegexPatternLen = 16384 + 1; const patternMaxLen = "c".repeat(kMaxRegexPatternLen); ``` Run query: ``` { fieldName: \{ "$regex": patternMaxLen} } ``` Previously, this query ran fine with a limit upwards of 32764 characters.
Sprint:
QE 2025-12-08, QE 2025-11-24
Case:
CAR Domain/s:
None

After upgrading our database several of our queries started failing with the error message

"Regular expression is invalid: pattern string is longer than the limit set by the application"

I've traced the relevant code to these following lines:

So I am fairly confident this problem was introduced with the following commit:

An option to change this limit via a config option would solve this regression for us.

is depended on by

COMPASS-10130 Investigate changes in SERVER-86326: Increase max regex pattern length to 32k

TOOLS-4020 Investigate changes in SERVER-86326: Increase max regex pattern length to 32k