SERVER-85932 Update README for cost model calibration setup (#40665)

GitOrigin-RevId: 3775c3777c1a5bf15e639925e834b08ab65d1868

buildscripts/cost_model/README.md

@@ -1,30 +1,93 @@
 # Cost Model Calibrator
 
-## Python virtual environment
+## Getting Started
 
-The following assumes you are using python from the MongoDB toolchain.
+### 1) Setup Mongod
 
-```
-/opt/mongodbtoolchain/v4/bin/python3
-```
+First, prepare the MongoDB server:
 
-### Getting started
-
-Make sure before running `start.py`, you have a locally running `mongod` instance (this must be run using the `mongo-python3` virtual environment, so do it before step 1 below).
+1. Activate the standard virtual environment:
 
 ```sh
-(mongo-python3) deactivate  # only if you have another python env activated
-sh> /opt/mongodbtoolchain/v4/bin/python3 -m venv cm  # create new env
-sh> source cm/bin/activate  # activate new env
-(cm) python -m pip install -r requirements.txt  # install required packages
-(cm) python start.py  # run the calibrator
-(cm) deactivate  # back to bash
-sh>
+source python3-venv/bin/activate
 ```
 
-### Install new packages
+2. Build server with optimizations (makes doc insertion faster):
 
 ```sh
-(cm) python -m pip install <package_name>     # install <package_name>
-(cm) python -m pip freeze > requirements.txt  # do not forget to update requirements.txt
+(python3-venv) bazel build --config=opt install-devcore
+```
+
+3. Run mongod instance:
+
+```sh
+(python3-venv) bazel-bin/install-mongod/bin/mongod --setParameter internalMeasureQueryExecutionTimeInNanoseconds=true
+```
+
+### 2) Setup Cost Model Calibrator
+
+In another terminal:
+
+1. Navigate to the cost model directory:
+
+```sh
+cd buildscripts/cost_model
+```
+
+2. Set up Python alias to use MongoDB toolchain:
+
+```sh
+alias python=/opt/mongodbtoolchain/v4/bin/python3
+```
+
+3. Deactivate any existing Python environment (if needed):
+
+```sh
+deactivate
+```
+
+4. Create new virtual environment:
+
+```sh
+/opt/mongodbtoolchain/v4/bin/python3 -m venv cm
+```
+
+5. Activate the new environment:
+
+```sh
+source cm/bin/activate
+```
+
+6. Install required packages:
+
+```sh
+(cm) python -m pip install -r requirements.txt
+```
+
+7. Run the calibrator:
+
+```sh
+(cm) python start.py
+```
+
+**Note:** For the first time it will take a while since it has to generate the data. Afterwards, as long as you aren't modifying the collections, you can comment out `await generator.populate_collections()` in `start.py` - this will make it a lot faster.
+
+8. When done, deactivate the environment:
+
+```sh
+(cm) deactivate
+```
+
+## Install New Packages
+
+1. Install the package:
+
+```sh
+(cm) python -m pip install <package_name>
+```
+
+2. Update requirements.txt:
+
+```sh
+(cm) python -m pip freeze > requirements.txt
 ```