chore: add build acceleration tricks (#4)

src/accelerate-build.md

@@ -4,15 +4,15 @@
 
 Using `sccache` configured with AWS S3 allows decreasing build time.
 
-## Install `sccache`
+### Install `sccache`
 
 macOS:
 
 ```bash
 brew install sccache
 ```
 
-## Add S3 config
+### Add S3 config
 
 We consider we have already configured AWS S3 storage with the following settings:
 
@@ -37,7 +37,7 @@ Run to apply these settings immediately:
 source ~/.zshrc
 ```
 
-## Build Gear node using `sccache`
+### Build Gear node using `sccache`
 
 We need to set the `RUSTC_WRAPPER` environment variable to `sccache`. Also, we need to set `CARGO_INCREMENTAL` to `0` as `sccache` doesn't work well when using incremental building. We can set these environment variables by prepending the `cargo` command in the shell:
 
@@ -55,22 +55,22 @@ RUSTC_WRAPPER=sccache CARGO_INCREMENTAL=0 cargo b -r
 
 `mold` is the linker that uses multiple CPU cores when linking.
 
-## Install `mold/sold`
+### Install `mold/sold`
 
-### macOS
+- macOS
 
-As `mold` doesn't support macOS we need to build `sold` manually.
+    As `mold` doesn't support macOS we need to build `sold` manually.
 
-```bash
-git clone https://github.com/bluewhalesystems/sold.git
-mkdir sold/build
-cd sold/build
-cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=c++ ..
-cmake --build . -j $(sysctl -n hw.ncpu)
-sudo cmake --build . --target install
-```
+    ```bash
+    git clone https://github.com/bluewhalesystems/sold.git
+    mkdir sold/build
+    cd sold/build
+    cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=c++ ..
+    cmake --build . -j $(sysctl -n hw.ncpu)
+    sudo cmake --build . --target install
+    ```
 
-## Configure `cargo` to use `mold/sold`
+### Configure `cargo` to use `mold/sold`
 
 To use `mold/sold` with Rust, create (or update) `.cargo/config.toml` at your home directory with the following:
 
@@ -81,3 +81,54 @@ rustflags = ["-C", "link-arg=--ld-path=/usr/local/bin/ld64.sold"]
 ```
 
 Then just run `cargo b [-r]` as usually.
+
+## Using prebuilt `librocksdb.a`
+
+You can use prebuilt static library for the `librocksdb-sys` crate to avoid rebuilding it everytime from C++ sources.
+
+The example below is for macOS:
+
+- Build the `librocksdb-sys` crate in the release profile:
+
+    ```bash
+    cargo b -rp librocksdb-sys
+    ```
+
+- Find the `librocksdb.a` file in the `target` directory:
+
+    ```bash
+    find target -name librocksdb.a
+    # -> target/release/build/librocksdb-sys-a0a228694895e8fd/out/librocksdb.a
+    ```
+
+- Copy `librocksdb.a` to some permanent directory:
+
+    ```bash
+    mkdir -p ~/lib
+    cp -fv path/to/librocksdb.a ~/lib/
+    ```
+
+- Install `bzip2`:
+
+    ```bash
+    brew install bzip2
+    ```
+
+- Set environment variables:
+
+    ```bash
+    export ROCKSDB_STATIC=1
+    export ROCKSDB_LIB_DIR=~/lib
+    export CARGO_TARGET_AARCH64_APPLE_DARWIN_RUSTFLAGS="-Clink-arg=-L/opt/homebrew/opt/bzip2/lib -Clink-arg=-lbz2"
+    ```
+
+Now the `librocksdb-sys` crate building will be mush faster.
+
+## Avoid rebuilding examples before pallet tests
+
+- Set the `__GEAR_WASM_BUILDER_NO_FEATURES_TRACKING` environment variable to `1`:
+
+    ```bash
+    export __GEAR_WASM_BUILDER_NO_FEATURES_TRACKING=1
+    cargo t -p pallet-gear
+    ```