puma--puma/docs/compile_options.md

Compile Options

There are some cflags provided to change Puma's default configuration for its C extension.

Query String, PUMA_QUERY_STRING_MAX_LENGTH

By default, the max length of QUERY_STRING is 1024 * 10. But you may want to adjust it to allow accept larger queries in GET requests.

For manual install, pass the PUMA_QUERY_STRING_MAX_LENGTH option like this:

gem install puma -- --with-cflags="-D PUMA_QUERY_STRING_MAX_LENGTH=64000"

For Bundler, use its configuration system:

bundle config build.puma --with-cflags="-D PUMA_QUERY_STRING_MAX_LENGTH=64000"