FastMCP.from_openapi() takes too much time to create instance.

[itaru2622]

I'm trying fastmcp.from_openapi() for OpenAPI spec which got from REST production server.

openAPI spec for production server has lots of paths and methods.
i.e: github REST API has over 1000 APIs in paths (num of path x methods).

I found it takes too much time to create instance as below:

num of API(path x methods) => seconds
8  =>  1.856                               // for GET /app*   to github
241 => 46.969                          //  for GET /repo* to github
636 => 122.529 (2min)           //  for  GET /* to github
1216 => 216.911 (3.6 min)     //  for any github APIs.

seconds measured with time.time(), i.e. user experience time, took diff just before/after FastMCP.from_openapi().

as the result, production mcp clients, such as VC copilot chat UI, often give up waiting FastMCP ready to serve when transport is stdio

[itaru2622]

my fast investigation with CProfile, it took most time in compress_schema(), occupying almost 87% of total time.

time occupations in compresss_schema() are:

function	percentage
copy.deepcopy	52%
_prune_unused_defs	17%
_walk_and_prune	13%

when I replaced copy.deepcopy to json.dumps+loads, it gets almost 1.24x faster than before.

num of API(path x methods) => seconds
8 => 1.431
241 => 36.753
636 => 98.472
1216 => 174.268  #  1.24x faster than before.

compresss_schema() occupies 72% of total time, and its NEW breakdowns are:

function	percentage
deepcopy by json	11 %
_prune_unused_defs	35 %
_walk_and_prune	26%

more investigations, more faster... I hope.
unfortunately, it is very hard to investigate more deeper, since _prune_unused_defs and _walk_and_prune have recursive calls (walk).
walk called more than 14 Kilo times for 8 APIs, and it calls 62 Kilo times for recursion and 2 Mega calls for further functions.
it maybe need restructuring for utilities/json_schema.py to get more faster.

[itaru2622]

I tested with new OpenAPI parser in main branch, and found:
It got enough performance, just few seconds for 1216 APIs under the same condition as the above.

pip install git+https://github.com/jlowin/fastmcp@main
export FASTMCP_EXPERIMENTAL_ENABLE_NEW_OPENAPI_PARSER=true

thank you, jlowin