feat: least connections strategy and fix databasePools computeIfAbsent (

#282)

common/lib/aws_pool_client.ts

@@ -24,4 +24,6 @@ export interface AwsPoolClient {
   getIdleCount(): number;
 
   getTotalCount(): number;
+
+  getActiveCount(): number;
 }

common/lib/internal_pooled_connection_provider.ts

@@ -33,40 +33,41 @@ import { Messages } from "./utils/messages";
 import { HostSelector } from "./host_selector";
 import { RandomHostSelector } from "./random_host_selector";
 import { InternalPoolMapping } from "./utils/internal_pool_mapping";
-import { logger } from "../logutils";
 import { RoundRobinHostSelector } from "./round_robin_host_selector";
 import { AwsPoolClient } from "./aws_pool_client";
 import { AwsPoolConfig } from "./aws_pool_config";
+import { LeastConnectionsHostSelector } from "./least_connections_host_selector";
 import { PoolClientWrapper } from "./pool_client_wrapper";
+import { logger } from "../logutils";
 
 export class InternalPooledConnectionProvider implements PooledConnectionProvider, CanReleaseResources {
-  private static readonly acceptedStrategies: Map<string, HostSelector> = new Map([
-    [RandomHostSelector.STRATEGY_NAME, new RandomHostSelector()],
-    [RoundRobinHostSelector.STRATEGY_NAME, new RoundRobinHostSelector()]
-  ]);
   static readonly CACHE_CLEANUP_NANOS: bigint = BigInt(60_000_000_000); // 60 minutes
   static readonly POOL_EXPIRATION_NANOS: bigint = BigInt(30_000_000_000); // 30 minutes
+  protected static databasePools: SlidingExpirationCache<string, any> = new SlidingExpirationCache(
+    InternalPooledConnectionProvider.CACHE_CLEANUP_NANOS,
+    (pool: any) => pool.getActiveCount() === 0,
+    (pool: any) => pool.end()
+  );
 
+  private static readonly acceptedStrategies: Map<string, HostSelector> = new Map([
+    [RandomHostSelector.STRATEGY_NAME, new RandomHostSelector()],
+    [RoundRobinHostSelector.STRATEGY_NAME, new RoundRobinHostSelector()],
+    [LeastConnectionsHostSelector.STRATEGY_NAME, new LeastConnectionsHostSelector(InternalPooledConnectionProvider.databasePools)]
+  ]);
   private readonly rdsUtil: RdsUtils = new RdsUtils();
   private readonly _poolMapping?: InternalPoolMapping;
   private readonly _poolConfig?: AwsPoolConfig;
   targetClient?: ClientWrapper;
   internalPool: AwsPoolClient | undefined;
 
-  protected databasePools: SlidingExpirationCache<PoolKey, any> = new SlidingExpirationCache(
-    InternalPooledConnectionProvider.CACHE_CLEANUP_NANOS,
-    (pool: any) => pool.getIdleCount() === pool.getTotalCount(),
-    (pool: any) => pool.end()
-  );
-
-  poolExpirationCheckNanos: bigint = InternalPooledConnectionProvider.POOL_EXPIRATION_NANOS; // 30 minutes
+  private static poolExpirationCheckNanos: bigint = InternalPooledConnectionProvider.POOL_EXPIRATION_NANOS; // 30 minutes
 
   constructor(poolConfig?: AwsPoolConfig);
   constructor(poolConfig?: AwsPoolConfig, mapping?: InternalPoolMapping);
   constructor(poolConfig?: AwsPoolConfig, mapping?: InternalPoolMapping, poolExpirationNanos?: bigint, poolCleanupNanos?: bigint) {
     this._poolMapping = mapping;
-    this.poolExpirationCheckNanos = poolExpirationNanos ?? InternalPooledConnectionProvider.POOL_EXPIRATION_NANOS;
-    this.databasePools.cleanupIntervalNs = poolCleanupNanos ?? InternalPooledConnectionProvider.CACHE_CLEANUP_NANOS;
+    InternalPooledConnectionProvider.poolExpirationCheckNanos = poolExpirationNanos ?? InternalPooledConnectionProvider.POOL_EXPIRATION_NANOS;
+    InternalPooledConnectionProvider.databasePools.cleanupIntervalNs = poolCleanupNanos ?? InternalPooledConnectionProvider.CACHE_CLEANUP_NANOS;
     this._poolConfig = poolConfig ?? new AwsPoolConfig({});
   }
 
@@ -107,25 +108,30 @@ export class InternalPooledConnectionProvider implements PooledConnectionProvide
 
     const dialect = pluginService.getDriverDialect();
     const preparedConfig = dialect.preparePoolClientProperties(props, this._poolConfig);
-
-    this.internalPool = this.databasePools.computeIfAbsent(
-      new PoolKey(connectionHostInfo.url, this.getPoolKey(connectionHostInfo, props)),
+    this.internalPool = InternalPooledConnectionProvider.databasePools.computeIfAbsent(
+      new PoolKey(connectionHostInfo.url, this.getPoolKey(connectionHostInfo, props)).getPoolKeyString(),
       () => dialect.getAwsPoolClient(preparedConfig),
-      this.poolExpirationCheckNanos
+      InternalPooledConnectionProvider.poolExpirationCheckNanos
     );
 
-    return await this.getPoolConnection(hostInfo, props);
+    return await this.getPoolConnection(connectionHostInfo, props);
   }
 
   async getPoolConnection(hostInfo: HostInfo, props: Map<string, string>) {
     return new PoolClientWrapper(await this.internalPool!.connect(), hostInfo, props);
   }
 
-  public async releaseResources() {
-    for (const [key, val] of this.databasePools.entries) {
-      val.item.releaseResources();
+  async releaseResources() {
+    for (const [_key, value] of InternalPooledConnectionProvider.databasePools.entries) {
+      if (value.item) {
+        await value.item.releaseResources();
+      }
     }
-    this.databasePools.clear();
+    InternalPooledConnectionProvider.clearDatabasePools();
+  }
+
+  static clearDatabasePools() {
+    InternalPooledConnectionProvider.databasePools.clear();
   }
 
   getHostInfoByStrategy(hosts: HostInfo[], role: HostRole, strategy: string, props?: Map<string, any>): HostInfo {
@@ -140,36 +146,30 @@ export class InternalPooledConnectionProvider implements PooledConnectionProvide
     return promisify(lookup)(host, {});
   }
 
-  getHostUrlSet(): Set<string> {
-    const hostUrls: Set<string> = new Set<string>();
-    for (const [key, _val] of this.databasePools.entries) {
-      hostUrls.add(key.getUrl());
-    }
-    return hostUrls;
-  }
-
   getHostCount() {
-    return this.databasePools.size;
+    return InternalPooledConnectionProvider.databasePools.size;
   }
 
-  getKeySet(): Set<PoolKey> {
-    return new Set<PoolKey>(this.databasePools.keys);
+  getKeySet(): Set<string> {
+    return new Set<string>(InternalPooledConnectionProvider.databasePools.keys);
   }
 
   getPoolKey(hostInfo: HostInfo, props: Map<string, any>) {
     return this._poolMapping?.getKey(hostInfo, props) ?? WrapperProperties.USER.get(props);
   }
 
   logConnections() {
-    if (this.databasePools.size === 0) {
+    if (InternalPooledConnectionProvider.databasePools.size === 0) {
       return;
     }
 
-    const l = Array.from(this.databasePools.entries).map(([v, k]) => [v.getPoolKeyString(), k.item.constructor.name]);
-    logger.debug(`Internal Pooled Connection: [${JSON.stringify(l)}]`);
+    const connections = Array.from(InternalPooledConnectionProvider.databasePools.entries).map(([v, k]) => [v, k.item.constructor.name]);
+    logger.debug(`Internal Pooled Connections: [\r\n${connections.join("\r\n")}\r\n]`);
   }
 
-  setDatabasePools(connectionPools: SlidingExpirationCache<PoolKey, any>): void {
-    this.databasePools = connectionPools;
+  // for testing only
+  setDatabasePools(connectionPools: SlidingExpirationCache<string, any>): void {
+    InternalPooledConnectionProvider.databasePools = connectionPools;
+    LeastConnectionsHostSelector.setDatabasePools(connectionPools);
   }
 }

common/lib/least_connections_host_selector.ts

@@ -0,0 +1,64 @@
+/*
+  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ 
+  Licensed under the Apache License, Version 2.0 (the "License").
+  You may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+ 
+  http://www.apache.org/licenses/LICENSE-2.0
+ 
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+*/
+
+import { HostSelector } from "./host_selector";
+import { HostInfo } from "./host_info";
+import { HostRole } from "./host_role";
+import { AwsWrapperError } from "./utils/errors";
+import { HostAvailability } from "./host_availability/host_availability";
+import { Messages } from "./utils/messages";
+import { SlidingExpirationCache } from "./utils/sliding_expiration_cache";
+
+export class LeastConnectionsHostSelector implements HostSelector {
+  protected static databasePools: SlidingExpirationCache<string, any>;
+  static readonly STRATEGY_NAME = "leastConnections";
+
+  constructor(databasePools: SlidingExpirationCache<string, any>) {
+    LeastConnectionsHostSelector.databasePools = databasePools;
+  }
+
+  getHost(hosts: HostInfo[], role: HostRole, props?: Map<string, any>): HostInfo {
+    const eligibleHosts: HostInfo[] = hosts
+      .filter((host: HostInfo) => host.role === role && host.availability === HostAvailability.AVAILABLE)
+      .sort((hostA: HostInfo, hostB: HostInfo) => {
+        const hostACount = this.getNumConnections(hostA, LeastConnectionsHostSelector.databasePools);
+        const hostBCount = this.getNumConnections(hostB, LeastConnectionsHostSelector.databasePools);
+        return hostACount < hostBCount ? -1 : hostACount > hostBCount ? 1 : 0;
+      });
+
+    if (eligibleHosts.length === 0) {
+      throw new AwsWrapperError(Messages.get("HostSelector.noHostsMatchingRole", role));
+    }
+    return eligibleHosts[0];
+  }
+
+  getNumConnections(hostInfo: HostInfo, databasePools: SlidingExpirationCache<string, any>): number {
+    let numConnections: number = 0;
+    const url: string = hostInfo.url;
+    for (const [key, val] of databasePools.map.entries()) {
+      if (!key.includes(url)) {
+        continue;
+      }
+      numConnections += val.item.getActiveCount();
+    }
+    return numConnections;
+  }
+
+  // for testing purposes only
+  static setDatabasePools(connectionPools: SlidingExpirationCache<string, any>): void {
+    LeastConnectionsHostSelector.databasePools = connectionPools;
+  }
+}

common/lib/mysql_client_wrapper.ts

@@ -1,12 +1,12 @@
 /*
   Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
-
+ 
   Licensed under the Apache License, Version 2.0 (the "License").
   You may not use this file except in compliance with the License.
   You may obtain a copy of the License at
-
+ 
   http://www.apache.org/licenses/LICENSE-2.0
-
+ 
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

common/lib/pg_client_wrapper.ts

@@ -1,12 +1,12 @@
 /*
   Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
-
+ 
   Licensed under the Apache License, Version 2.0 (the "License").
   You may not use this file except in compliance with the License.
   You may obtain a copy of the License at
-
+ 
   http://www.apache.org/licenses/LICENSE-2.0
-
+ 
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

common/lib/pool_client_wrapper.ts

@@ -1,12 +1,12 @@
 /*
   Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
-
+ 
   Licensed under the Apache License, Version 2.0 (the "License").
   You may not use this file except in compliance with the License.
   You may obtain a copy of the License at
-
+ 
   http://www.apache.org/licenses/LICENSE-2.0
-
+ 
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

common/lib/utils/pool_key.ts

@@ -27,7 +27,11 @@ export class PoolKey {
     return this.url;
   }
 
+  getExtraKey(): string {
+    return this.extraKey;
+  }
+
   getPoolKeyString(): string {
-    return "PoolKey [url=" + this.url + ", extraKey=" + this.extraKey + "]";
+    return `PoolKey [url=${this.getUrl()}, extraKey=${this.getExtraKey()}]`;
   }
 }

common/lib/utils/sliding_expiration_cache.ts

@@ -61,6 +61,7 @@ export class SlidingExpirationCache<K, V> {
   get keys() {
     return this.map.keys();
   }
+
   set cleanupIntervalNs(value: bigint) {
     this._cleanupIntervalNanos = value;
   }

mysql/lib/dialect/mysql2_driver_dialect.ts

@@ -1,12 +1,12 @@
 /*
   Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
-
+ 
   Licensed under the Apache License, Version 2.0 (the "License").
   You may not use this file except in compliance with the License.
   You may obtain a copy of the License at
-
+ 
   http://www.apache.org/licenses/LICENSE-2.0
-
+ 
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

mysql/lib/mysql_pool_client.ts

@@ -50,6 +50,10 @@ export class AwsMysqlPoolClient implements AwsPoolClient {
     return this.targetPool.pool._allConnections.length;
   }
 
+  getActiveCount(): number {
+    return this.getTotalCount() - this.getIdleCount();
+  }
+
   async releaseResources(): Promise<void> {
     await this.targetPool.end();
   }

pg/lib/pg_pool_client.ts

@@ -57,6 +57,10 @@ export class AwsPgPoolClient implements AwsPoolClient {
     return this.targetPool.totalCount;
   }
 
+  getActiveCount(): number {
+    return this.getTotalCount() - this.getIdleCount();
+  }
+
   async releaseResources(): Promise<void> {
     await this.targetPool.end();
   }