feat: configurable read_pool_size (#76)

* configurable `read_pool_size`

* optional env var `HQL_READ_POOL_SIZE`

config

@@ -36,6 +36,20 @@ HQL_NODES="
 # default: false
 HQL_LOG_STATEMENTS=true
 
+# The size of the pooled connections for local database reads.
+#
+# Do not confuse this with a pool size for network databases, as it is much more efficient.
+# You cant' really translate between them, because it depends on many factors, but if you
+# assume a factor of 10 is a good start. This means, if you needed a (read) pool size of 40
+# connections for something like a postgres before, you should start at a `read_pool_size` of
+# 4.
+#
+# Keep in mind that this pool is only used for reads and writes will travel through the Raft
+# and have their own dedicated connection.
+#
+# default: 4
+HQL_READ_POOL_SIZE=4
+
 # Enables immediate flush + sync to disk after each Log Store Batch.
 # The situations where you would need this are very rare, and you
 # should use it with care.

hiqlite/src/config.rs

@@ -44,6 +44,19 @@ pub struct NodeConfig {
     /// The internal cache size for prepared statements. The default is `1024` which could be
     /// reduced in very heavily memory-constrained environments.
     pub prepared_statement_cache_capacity: usize,
+    /// The size of the pooled connections for local database reads.
+    ///
+    /// Do not confuse this with a pool size for network databases, as it is much more efficient.
+    /// You cant' really translate between them, because it depends on many factors, but if you
+    /// assume a factor of 10 is a good start. This means, if you needed a (read) pool size of 40
+    /// connections for something like a postgres before, you should start at a `read_pool_size` of
+    /// 4.
+    ///
+    /// Keep in mind that this pool is only used for reads and writes will travel through the Raft
+    /// and have their own dedicated connection.
+    ///
+    /// default: 4
+    pub read_pool_size: usize,
     /// Enables immediate flush + sync to disk after each Log Store Batch.
     /// The situations where you would need this are very rare, and you should use it with care.
     ///
@@ -92,6 +105,7 @@ impl Default for NodeConfig {
             filename_db: "hiqlite.db".into(),
             log_statements: false,
             prepared_statement_cache_capacity: 1024,
+            read_pool_size: 4,
             sync_immediate: false,
             raft_config: Self::default_raft_config(10_000),
             tls_raft: None,
@@ -193,6 +207,10 @@ impl NodeConfig {
                 .parse()
                 .expect("Cannot parse HQL_LOG_STATEMENTS to u64"),
             prepared_statement_cache_capacity: 1024,
+            read_pool_size: env::var("HQL_READ_POOL_SIZE")
+                .unwrap_or_else(|_| "4".to_string())
+                .parse()
+                .expect("Cannot parse HQL_READ_POOL_SIZE to usize"),
             sync_immediate: env::var("HQL_SYNC_IMMEDIATE")
                 .unwrap_or_else(|_| "false".to_string())
                 .parse()

hiqlite/src/store/mod.rs

@@ -48,6 +48,7 @@ pub(crate) async fn start_raft_db(
         node_config.node_id,
         node_config.log_statements,
         node_config.prepared_statement_cache_capacity,
+        node_config.read_pool_size,
         #[cfg(feature = "s3")]
         node_config.s3_config,
     )

hiqlite/src/store/state_machine/sqlite/state_machine.rs

@@ -122,6 +122,7 @@ impl StateMachineSqlite {
         this_node: NodeId,
         log_statements: bool,
         prepared_statement_cache_capacity: usize,
+        read_pool_size: usize,
         #[cfg(feature = "s3")] s3_config: Option<Arc<crate::s3::S3Config>>,
     ) -> Result<StateMachineSqlite, StorageError<NodeId>> {
         // IMPORTANT: Do NOT change the order of the db exists check!
@@ -156,6 +157,7 @@ impl StateMachineSqlite {
             path_db.as_ref(),
             filename_db,
             prepared_statement_cache_capacity,
+            read_pool_size,
         )
         .await
         .map_err(|err| StorageError::IO {
@@ -302,13 +304,12 @@ impl StateMachineSqlite {
         path: &str,
         filename_db: &str,
         prepared_statement_cache_capacity: usize,
+        pool_size: usize,
     ) -> Result<SqlitePool, Error> {
         let path_full = format!("{}/{}", path, filename_db);
 
-        // TODO configurable read pool size
-        let amount = 4;
-        let mut conns = Vec::with_capacity(amount);
-        for _ in 0..amount {
+        let mut conns = Vec::with_capacity(pool_size);
+        for _ in 0..pool_size {
             let mut conn = Self::connect(
                 path.to_string(),
                 filename_db.to_string(),