chore: support for common interface to get a session to support multiplexed session (#2204)

This PR contains the common interface class SessionFactory which will be responsible for the creation of the Session Pool and the Multiplexed Session(if the env variable would be set to true) upon client initialization.

This PR also contains the getSession method which will return the session(multiplexed/regular) based upon the env variable value.

Author: alkatrivedi

observability-test/database.ts

@@ -47,6 +47,7 @@ import {Instance, MutationGroup, Spanner} from '../src';
 import * as pfy from '@google-cloud/promisify';
 import {grpc} from 'google-gax';
 import {MockError} from '../test/mockserver/mockspanner';
+import {FakeSessionFactory} from '../test/database';
 const {generateWithAllSpansHaveDBName} = require('./helper');
 
 const fakePfy = extend({}, pfy, {
@@ -234,6 +235,7 @@ describe('Database', () => {
       './codec': {codec: fakeCodec},
       './partial-result-stream': {partialResultStream: fakePartialResultStream},
       './session-pool': {SessionPool: FakeSessionPool},
+      './session-factory': {SessionFactory: FakeSessionFactory},
       './session': {Session: FakeSession},
       './table': {Table: FakeTable},
       './transaction-runner': {

src/database.ts

@@ -36,6 +36,7 @@ import {
 } from 'google-gax';
 import {Backup} from './backup';
 import {BatchTransaction, TransactionIdentifier} from './batch-transaction';
+import {SessionFactory, SessionFactoryInterface} from './session-factory';
 import {
   google as databaseAdmin,
   google,
@@ -111,7 +112,6 @@ import {
   setSpanErrorAndException,
   traceConfig,
 } from './instrument';
-
 export type GetDatabaseRolesCallback = RequestCallback<
   IDatabaseRole,
   databaseAdmin.spanner.admin.database.v1.IListDatabaseRolesResponse
@@ -339,6 +339,7 @@ class Database extends common.GrpcServiceObject {
   private instance: Instance;
   formattedName_: string;
   pool_: SessionPoolInterface;
+  sessionFactory_: SessionFactoryInterface;
   queryOptions_?: spannerClient.spanner.v1.ExecuteSqlRequest.IQueryOptions;
   commonHeaders_: {[k: string]: string};
   request: DatabaseRequest;
@@ -450,15 +451,6 @@ class Database extends common.GrpcServiceObject {
       },
     } as {} as ServiceObjectConfig);
 
-    this.pool_ =
-      typeof poolOptions === 'function'
-        ? new (poolOptions as SessionPoolConstructor)(this, null)
-        : new SessionPool(this, poolOptions);
-    const sessionPoolInstance = this.pool_ as SessionPool;
-    if (sessionPoolInstance) {
-      sessionPoolInstance._observabilityOptions =
-        instance._observabilityOptions;
-    }
     if (typeof poolOptions === 'object') {
       this.databaseRole = poolOptions.databaseRole || null;
       this.labels = poolOptions.labels || null;
@@ -480,8 +472,13 @@ class Database extends common.GrpcServiceObject {
 
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     this.requestStream = instance.requestStream as any;
-    this.pool_.on('error', this.emit.bind(this, 'error'));
-    this.pool_.open();
+    this.sessionFactory_ = new SessionFactory(this, name, poolOptions);
+    this.pool_ = this.sessionFactory_.getPool();
+    const sessionPoolInstance = this.pool_ as SessionPool;
+    if (sessionPoolInstance) {
+      sessionPoolInstance._observabilityOptions =
+        instance._observabilityOptions;
+    }
     this.queryOptions_ = Object.assign(
       Object.assign({}, queryOptions),
       Database.getEnvironmentQueryOptions()

src/multiplexed-session.ts

@@ -17,7 +17,7 @@
 import {EventEmitter} from 'events';
 import {Database} from './database';
 import {Session} from './session';
-import {GetSessionCallback} from './session-pool';
+import {GetSessionCallback} from './session-factory';
 import {
   ObservabilityOptions,
   getActiveOrNoopSpan,
@@ -38,7 +38,7 @@ export const MUX_SESSION_CREATE_ERROR = 'mux-session-create-error';
  * @constructs MultiplexedSessionInterface
  * @param {Database} database The database to create a multiplexed session for.
  */
-export interface MultiplexedSessionInterface {
+export interface MultiplexedSessionInterface extends EventEmitter {
   /**
    * When called creates a multiplexed session.
    *
@@ -71,6 +71,7 @@ export class MultiplexedSession
   database: Database;
   // frequency to create new mux session
   refreshRate: number;
+  isMultiplexedEnabled: boolean;
   _multiplexedSession: Session | null;
   _refreshHandle!: NodeJS.Timer;
   _observabilityOptions?: ObservabilityOptions;
@@ -81,6 +82,9 @@ export class MultiplexedSession
     this.refreshRate = 7;
     this._multiplexedSession = null;
     this._observabilityOptions = database._observabilityOptions;
+    process.env.GOOGLE_CLOUD_SPANNER_MULTIPLEXED_SESSIONS === 'true'
+      ? (this.isMultiplexedEnabled = true)
+      : (this.isMultiplexedEnabled = false);
   }
 
   /**

src/session-factory.ts

@@ -0,0 +1,161 @@
+/*!
+ * Copyright 2024 Google LLC. 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 {Database, Session, Transaction} from '.';
+import {
+  MultiplexedSession,
+  MultiplexedSessionInterface,
+} from './multiplexed-session';
+import {
+  SessionPool,
+  SessionPoolInterface,
+  SessionPoolOptions,
+} from './session-pool';
+import {SessionPoolConstructor} from './database';
+import {ServiceObjectConfig} from '@google-cloud/common';
+const common = require('./common-grpc/service-object');
+
+/**
+ * @callback GetSessionCallback
+ * @param {?Error} error Request error, if any.
+ * @param {Session} session The read-write session.
+ * @param {Transaction} transaction The transaction object.
+ */
+export interface GetSessionCallback {
+  (
+    err: Error | null,
+    session?: Session | null,
+    transaction?: Transaction | null
+  ): void;
+}
+
+/**
+ * Interface for implementing session-factory logic.
+ *
+ * @interface SessionFactoryInterface
+ */
+export interface SessionFactoryInterface {
+  /**
+   * When called returns a session.
+   *
+   * @name SessionFactoryInterface#getSession
+   * @param {GetSessionCallback} callback The callback function.
+   */
+  getSession(callback: GetSessionCallback): void;
+
+  /**
+   * When called returns the pool object.
+   *
+   * @name SessionFactoryInterface#getPool
+   */
+  getPool(): SessionPoolInterface;
+
+  /**
+   * To be called when releasing a session.
+   *
+   * @name SessionFactoryInterface#release
+   * @param {Session} session The session to be released.
+   */
+  release(session: Session): void;
+}
+
+/**
+ * Creates a SessionFactory object to manage the creation of
+ *      session-pool and multiplexed session.
+ *
+ * @class
+ *
+ * @param {Database} database Database object.
+ * @param {String} name Name of the database.
+ * @param {SessionPoolOptions|SessionPoolInterface} options Session pool
+ *     configuration options or custom pool inteface.
+ */
+export class SessionFactory
+  extends common.GrpcServiceObject
+  implements SessionFactoryInterface
+{
+  multiplexedSession_: MultiplexedSessionInterface;
+  pool_: SessionPoolInterface;
+  constructor(
+    database: Database,
+    name: String,
+    poolOptions?: SessionPoolConstructor | SessionPoolOptions
+  ) {
+    super({
+      parent: database,
+      id: name,
+    } as {} as ServiceObjectConfig);
+    this.pool_ =
+      typeof poolOptions === 'function'
+        ? new (poolOptions as SessionPoolConstructor)(database, null)
+        : new SessionPool(database, poolOptions);
+    this.pool_.on('error', this.emit.bind(database, 'error'));
+    this.pool_.open();
+    this.multiplexedSession_ = new MultiplexedSession(database);
+    // Multiplexed sessions should only be created if its enabled.
+    if ((this.multiplexedSession_ as MultiplexedSession).isMultiplexedEnabled) {
+      this.multiplexedSession_.on('error', this.emit.bind(database, 'error'));
+      this.multiplexedSession_.createSession();
+    }
+  }
+
+  /**
+   * Retrieves a session, either a regular session or a multiplexed session, based on the environment variable configuration.
+   *
+   * If the environment variable `GOOGLE_CLOUD_SPANNER_MULTIPLEXED_SESSIONS` is set to `true`, the method will attempt to
+   * retrieve a multiplexed session. Otherwise, it will retrieve a session from the regular pool.
+   *
+   * @param {GetSessionCallback} callback The callback function.
+   */
+
+  getSession(callback: GetSessionCallback): void {
+    const sessionHandler = (this.multiplexedSession_ as MultiplexedSession)
+      .isMultiplexedEnabled
+      ? this.multiplexedSession_
+      : this.pool_;
+
+    sessionHandler!.getSession((err, session) => callback(err, session));
+  }
+
+  /**
+   * Returns the regular session pool object.
+   *
+   * @returns {SessionPoolInterface} The session pool used by current instance.
+   */
+
+  getPool(): SessionPoolInterface {
+    return this.pool_;
+  }
+
+  /**
+   * Releases a session back to the session pool.
+   *
+   * This method returns a session to the pool after it is no longer needed.
+   * It is a no-op for multiplexed sessions.
+   *
+   * @param {Session} session - The session to be released. This should be an instance of `Session` that was
+   * previously acquired from the session pool.
+   *
+   * @throws {Error} If the session is invalid or cannot be released.
+   */
+  release(session: Session): void {
+    if (
+      !(this.multiplexedSession_ as MultiplexedSession).isMultiplexedEnabled
+    ) {
+      this.pool_.release(session);
+    }
+  }
+}

src/session-pool.ts

@@ -30,7 +30,7 @@ import {
   setSpanErrorAndException,
   startTrace,
 } from './instrument';
-
+import {GetSessionCallback} from './session-factory';
 import {
   isDatabaseNotFoundError,
   isInstanceNotFoundError,
@@ -59,20 +59,6 @@ export interface GetWriteSessionCallback {
   ): void;
 }
 
-/**
- * @callback GetSessionCallback
- * @param {?Error} error Request error, if any.
- * @param {Session} session The read-write session.
- * @param {Transaction} transaction The transaction object.
- */
-export interface GetSessionCallback {
-  (
-    err: Error | null,
-    session?: Session | null,
-    transaction?: Transaction | null
-  ): void;
-}
-
 /**
  * Interface for implementing custom session pooling logic, it should extend the
  * {@link https://nodejs.org/api/events.html|EventEmitter} class and emit any