feat: Add benchmark for store read/write (#5312)

Add benchmark for reading / writing from store.

See #4771

```
cd chain/network/benches
rm -rf /tmp/xxxxx ; cargo bench benchmark_db
```

TODO:
- [x] Add tempdir
- [x] Pregenerate keys
- [x] Add stats to see number of entries read successfully
- [x] Why we can only read 48.5% entries back when we write them to DB?
- [x] Move code to a better place
- [x] Document what the benchmark does

core/store/Cargo.toml

@@ -37,6 +37,10 @@ rand = "0.7"
 name = "trie_bench"
 harness = false
 
+[[bench]]
+name = "store_bench"
+harness = false
+
 [features]
 default = []
 no_cache = []

core/store/benches/store_bench.rs

@@ -0,0 +1,99 @@
+#[macro_use]
+extern crate bencher;
+
+use bencher::{black_box, Bencher};
+use near_primitives::borsh::maybestd::sync::Arc;
+use near_primitives::errors::StorageError;
+use near_store::db::DBCol::ColBlockMerkleTree;
+use near_store::{create_store, DBCol, Store};
+use std::time::{Duration, Instant};
+
+/// Run a benchmark to generate `num_keys` keys, each of size `key_size`, then write then
+/// in random order to column `col` in store, and then read keys back from `col` in random order.
+/// Works only for column configured without reference counting, that is `.is_rc() == false`.
+fn benchmark_write_then_read_successful(
+    bench: &mut Bencher,
+    num_keys: usize,
+    key_size: usize,
+    max_value_size: usize,
+    col: DBCol,
+) {
+    let store = create_store_in_random_folder();
+    let keys = generate_keys(num_keys, key_size);
+    write_to_db(&store, &keys, max_value_size, col);
+
+    bench.iter(move || {
+        let start = Instant::now();
+
+        let read_records = read_from_db(&store, &keys, col);
+        let took = start.elapsed();
+        println!(
+            "took on avg {:?} op per sec {} got {}/{}",
+            took / (num_keys as u32),
+            (num_keys as u128) * Duration::from_secs(1).as_nanos() / took.as_nanos(),
+            read_records,
+            keys.len()
+        );
+    });
+}
+
+/// Create `Store` in a random folder.
+fn create_store_in_random_folder() -> Arc<Store> {
+    let tmp_dir = tempfile::Builder::new().prefix("_test_clear_column").tempdir().unwrap();
+    let store = create_store(tmp_dir.path());
+    store
+}
+
+/// Generate `count` keys of `key_size` length.
+fn generate_keys(count: usize, key_size: usize) -> Vec<Vec<u8>> {
+    let mut res: Vec<Vec<u8>> = Vec::new();
+    for _k in 0..count {
+        let key: Vec<u8> = (0..key_size).map(|_| rand::random::<u8>()).collect();
+
+        res.push(key)
+    }
+    res
+}
+
+/// Read from DB value for given `kyes` in random order for `col`.
+/// Works only for column configured without reference counting, that is `.is_rc() == false`.
+fn read_from_db(store: &Arc<Store>, keys: &Vec<Vec<u8>>, col: DBCol) -> usize {
+    let mut read = 0;
+    for _k in 0..keys.len() {
+        let r = rand::random::<u32>() % (keys.len() as u32);
+        let key = &keys[r as usize];
+
+        let val = store.get(col, key.as_ref()).map_err(|_| StorageError::StorageInternalError);
+
+        if let Ok(Some(x)) = val {
+            black_box(x);
+            read += 1;
+        }
+    }
+    read
+}
+
+/// Write random value of size between `0` and `max_value_size` to given `keys` at specific column
+/// `col.`
+/// Works only for column configured without reference counting, that is `.is_rc() == false`.
+fn write_to_db(store: &Arc<Store>, keys: &[Vec<u8>], max_value_size: usize, col: DBCol) {
+    let mut store_update = store.store_update();
+    for key in keys.iter() {
+        let x: usize = rand::random::<usize>() % max_value_size;
+        let val: Vec<u8> = (0..x).map(|_| rand::random::<u8>()).collect();
+        // NOTE:  this
+        store_update.set(col, key.as_slice().clone(), &val);
+    }
+    store_update.commit().unwrap();
+}
+
+fn benchmark_write_then_read_successful_10m(bench: &mut Bencher) {
+    // By adding logs, I've seen a lot of write to keys with size 40, an values with sizes
+    // between 10 .. 333.
+    // NOTE: ColBlockMerkleTree was chosen to be a column, where `.is_rc() == false`.
+    benchmark_write_then_read_successful(bench, 10_000_000, 40, 333, ColBlockMerkleTree);
+}
+
+benchmark_group!(benches, benchmark_write_then_read_successful_10m);
+
+benchmark_main!(benches);