sharding

Cargo.lock

@@ -72,6 +72,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "cpufeatures"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "95059428f66df56b63431fdb4e1947ed2190586af5c5a8a8b71122bdf5a7f469"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "crypto-common"
 version = "0.1.1"
@@ -342,6 +351,7 @@ dependencies = [
  "chrono",
  "md-5",
  "rand",
+ "sha-1",
  "tokio",
 ]
 
@@ -400,6 +410,17 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
+[[package]]
+name = "sha-1"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "028f48d513f9678cda28f6e4064755b3fbb2af6acd672f2c209b62323f7aea0f"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "digest",
+]
+
 [[package]]
 name = "signal-hook-registry"
 version = "1.4.0"

Cargo.toml

@@ -13,3 +13,4 @@ bb8 = "*"
 async-trait = "*"
 rand = "*"
 chrono = "0.4"
+sha-1 = "*"

src/main.rs

@@ -30,6 +30,7 @@ mod errors;
 mod messages;
 mod pool;
 mod server;
+mod sharding;
 
 // Support for query cancellation: this maps our process_ids and
 // secret keys to the backend's.
@@ -41,7 +42,7 @@ use pool::{ClientServerMap, ConnectionPool};
 async fn main() {
     println!("> Welcome to PgCat! Meow.");
 
-    let addr = "0.0.0.0:5433";
+    let addr = "0.0.0.0:6432";
     let listener = match TcpListener::bind(addr).await {
         Ok(sock) => sock,
         Err(err) => {

src/pool.rs

@@ -28,8 +28,8 @@ const POOL_SIZE: u32 = 15;
 
 #[derive(Clone)]
 pub struct ConnectionPool {
-    databases: Vec<Pool<ServerPool>>,
+    databases: Vec<Vec<Pool<ServerPool>>>,
-    addresses: Vec<Address>,
+    addresses: Vec<Vec<Address>>,
     round_robin: Counter,
     banlist: BanList,
 }
@@ -62,8 +62,8 @@ impl ConnectionPool {
         }
 
         ConnectionPool {
-            databases: databases,
+            databases: vec![databases],
-            addresses: addresses,
+            addresses: vec![addresses],
             round_robin: Arc::new(AtomicUsize::new(0)),
             banlist: Arc::new(Mutex::new(HashMap::new())),
         }
@@ -72,36 +72,27 @@ impl ConnectionPool {
     /// Get a connection from the pool. Either round-robin or pick a specific one in case they are sharded.
     pub async fn get(
         &self,
-        index: Option<usize>,
+        shard: Option<usize>,
     ) -> Result<(PooledConnection<'_, ServerPool>, Address), Error> {
-        match index {
+        // Set this to false to gain ~3-4% speed.
-            // Asking for a specific database, must be sharded.
+        let with_health_check = true;
-            // No failover here.
+
-            Some(index) => {
+        let shard = match shard {
-                assert!(index < self.databases.len());
+            Some(shard) => shard,
-                match self.databases[index].get().await {
+            None => 0, // TODO: pick a shard at random
-                    Ok(conn) => Ok((conn, self.addresses[index].clone())),
+        };
-                    Err(err) => {
-                        println!(">> Shard {} down: {:?}", index, err);
-                        Err(Error::ServerTimeout)
-                    }
-                }
-            }
 
-            // Any database is fine, we're using round-robin here.
-            // Failover included if the server doesn't answer a health check.
-            None => {
         loop {
             let index =
-                        self.round_robin.fetch_add(1, Ordering::SeqCst) % self.databases.len();
+                self.round_robin.fetch_add(1, Ordering::SeqCst) % self.databases[shard].len();
-                    let address = self.addresses[index].clone();
+            let address = self.addresses[shard][index].clone();
 
             if self.is_banned(&address) {
                 continue;
             }
 
             // Check if we can connect
-                    let mut conn = match self.databases[index].get().await {
+            let mut conn = match self.databases[shard][index].get().await {
                 Ok(conn) => conn,
                 Err(err) => {
                     println!(">> Banning replica {}, error: {:?}", index, err);
@@ -110,7 +101,11 @@ impl ConnectionPool {
                 }
             };
 
-                    // Check if this server is alive with a health check
+            if !with_health_check {
+                return Ok((conn, address));
+            }
+
+            // // Check if this server is alive with a health check
             let server = &mut *conn;
 
             match tokio::time::timeout(
@@ -131,8 +126,6 @@ impl ConnectionPool {
             }
         }
     }
-        }
-    }
 
     /// Ban an address (i.e. replica). It no longer will serve
     /// traffic for any new transactions. Existing transactions on that replica
@@ -180,6 +173,10 @@ impl ConnectionPool {
             None => false,
         }
     }
+
+    pub fn shards(&self) -> usize {
+        self.databases.len()
+    }
 }
 
 pub struct ServerPool {

src/sharding.rs

@@ -0,0 +1,33 @@
+use sha1::{Digest, Sha1};
+
+pub struct Sharder {
+    shards: usize,
+}
+
+impl Sharder {
+    pub fn new(shards: usize) -> Sharder {
+        Sharder { shards: shards }
+    }
+
+    pub fn sha1(&self, key: &[u8]) -> usize {
+        let mut hasher = Sha1::new();
+        hasher.update(key);
+        let result = hasher.finalize_reset();
+
+        let i = u32::from_le_bytes(result[result.len() - 4..result.len()].try_into().unwrap());
+        i as usize % self.shards
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_sha1() {
+        let sharder = Sharder::new(12);
+        let key = b"1234";
+        let shard = sharder.sha1(key);
+        assert_eq!(shard, 1);
+    }
+}