[10/N] feat(sqsim): add functional scenario suite

service/internal/sqldb/BUILD.bazel

@@ -0,0 +1,18 @@
+load("@rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["pool.go"],
+    importpath = "github.com/uber/submitqueue/service/internal/sqldb",
+    visibility = ["//service:__subpackages__"],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = ["pool_test.go"],
+    embed = [":go_default_library"],
+    deps = [
+        "@com_github_stretchr_testify//assert:go_default_library",
+        "@com_github_stretchr_testify//require:go_default_library",
+    ],
+)

service/internal/sqldb/pool.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2026 Uber Technologies, Inc.
+//
+// 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.
+
+// Package sqldb contains SQL database wiring helpers shared by services.
+package sqldb
+
+import (
+	"database/sql"
+	"fmt"
+	"strconv"
+)
+
+// ConfigureMaxOpenConnections applies a positive connection limit encoded as a
+// decimal string. It retains up to the same number of idle connections so a
+// busy bounded pool reuses sockets instead of repeatedly opening new ones. An
+// empty string or zero preserves database/sql defaults.
+func ConfigureMaxOpenConnections(db *sql.DB, value string) error {
+	if db == nil {
+		return fmt.Errorf("database is required")
+	}
+	if value == "" {
+		return nil
+	}
+	maxOpen, err := strconv.Atoi(value)
+	if err != nil {
+		return fmt.Errorf("parse maximum open connections %q: %w", value, err)
+	}
+	if maxOpen < 0 {
+		return fmt.Errorf("maximum open connections must be non-negative")
+	}
+	if maxOpen > 0 {
+		db.SetMaxOpenConns(maxOpen)
+		db.SetMaxIdleConns(maxOpen)
+	}
+	return nil
+}

service/internal/sqldb/pool_test.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2026 Uber Technologies, Inc.
+//
+// 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.
+
+package sqldb
+
+import (
+	"database/sql"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestConfigureMaxOpenConnections(t *testing.T) {
+	tests := []struct {
+		name    string
+		value   string
+		want    int
+		wantErr bool
+	}{
+		{name: "empty preserves default", value: "", want: 0},
+		{name: "zero preserves default", value: "0", want: 0},
+		{name: "positive applies limit", value: "32", want: 32},
+		{name: "negative is rejected", value: "-1", wantErr: true},
+		{name: "invalid is rejected", value: "many", wantErr: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			db := &sql.DB{}
+			err := ConfigureMaxOpenConnections(db, tt.value)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, db.Stats().MaxOpenConnections)
+		})
+	}
+}

service/runway/server/BUILD.bazel

@@ -19,6 +19,7 @@ go_library(
         "//runway/controller/mergeconflictcheck:go_default_library",
         "//runway/extension/merger:go_default_library",
         "//runway/extension/merger/noop:go_default_library",
+        "//service/internal/sqldb:go_default_library",
         "//sqsim/adapter/merger:go_default_library",
         "//sqsim/model:go_default_library",
         "@com_github_go_sql_driver_mysql//:go_default_library",

service/runway/server/main.go

@@ -41,6 +41,7 @@ import (
 	"github.com/uber/submitqueue/runway/controller/mergeconflictcheck"
 	"github.com/uber/submitqueue/runway/extension/merger"
 	"github.com/uber/submitqueue/runway/extension/merger/noop"
+	"github.com/uber/submitqueue/service/internal/sqldb"
 	simmerger "github.com/uber/submitqueue/sqsim/adapter/merger"
 	"github.com/uber/submitqueue/sqsim/model"
 	"go.uber.org/zap"
@@ -131,6 +132,9 @@ func run() error {
 		return fmt.Errorf("failed to open queue database: %w", err)
 	}
 	defer queueDB.Close()
+	if err := sqldb.ConfigureMaxOpenConnections(queueDB, os.Getenv("QUEUE_MYSQL_MAX_OPEN_CONNECTIONS")); err != nil {
+		return fmt.Errorf("configure queue database connection limit: %w", err)
+	}
 
 	mysqlQueue, err := queueMySQL.NewQueue(queueMySQL.Params{
 		DB:           queueDB,

service/submitqueue/docker-compose.yml

@@ -53,6 +53,7 @@ services:
       - MYSQL_DSN=root:root@tcp(mysql-app:3306)/submitqueue?parseTime=true
       # Queue infrastructure connection (separate database)
       - QUEUE_MYSQL_DSN=root:root@tcp(mysql-queue:3306)/submitqueue?parseTime=true
+      - QUEUE_MYSQL_MAX_OPEN_CONNECTIONS=${QUEUE_MYSQL_MAX_OPEN_CONNECTIONS:-}
       # Path to YAML queue configuration baked into the image
       - QUEUE_CONFIG_PATH=/root/queues.yaml
       # Stable subscriber name for the request-log consumer
@@ -75,6 +76,7 @@ services:
       - MYSQL_DSN=root:root@tcp(mysql-app:3306)/submitqueue?parseTime=true
       # Queue infrastructure connection (separate database)
       - QUEUE_MYSQL_DSN=root:root@tcp(mysql-queue:3306)/submitqueue?parseTime=true
+      - QUEUE_MYSQL_MAX_OPEN_CONNECTIONS=${QUEUE_MYSQL_MAX_OPEN_CONNECTIONS:-}
       - HOSTNAME=orchestrator-dev
       - SQSIM_SCENARIO_PATH=${SQSIM_SCENARIO_PATH:-}
     volumes:
@@ -100,6 +102,7 @@ services:
       - PORT=:8080
       # Queue infrastructure connection (shared with the orchestrator)
       - QUEUE_MYSQL_DSN=root:root@tcp(mysql-queue:3306)/submitqueue?parseTime=true
+      - QUEUE_MYSQL_MAX_OPEN_CONNECTIONS=${QUEUE_MYSQL_MAX_OPEN_CONNECTIONS:-}
       - HOSTNAME=runway-dev
       - SQSIM_SCENARIO_PATH=${SQSIM_SCENARIO_PATH:-}
     volumes:

service/submitqueue/gateway/server/BUILD.bazel

@@ -19,6 +19,7 @@ go_library(
         "//platform/extension/counter/mysql:go_default_library",
         "//platform/extension/messagequeue:go_default_library",
         "//platform/extension/messagequeue/mysql:go_default_library",
+        "//service/internal/sqldb:go_default_library",
         "//service/submitqueue/gateway/server/mapper:go_default_library",
         "//submitqueue/core/topickey:go_default_library",
         "//submitqueue/extension/queueconfig/yaml:go_default_library",

service/submitqueue/gateway/server/main.go

@@ -36,6 +36,7 @@ import (
 	mysqlcounter "github.com/uber/submitqueue/platform/extension/counter/mysql"
 	extqueue "github.com/uber/submitqueue/platform/extension/messagequeue"
 	queueMySQL "github.com/uber/submitqueue/platform/extension/messagequeue/mysql"
+	"github.com/uber/submitqueue/service/internal/sqldb"
 	"github.com/uber/submitqueue/service/submitqueue/gateway/server/mapper"
 	"github.com/uber/submitqueue/submitqueue/core/topickey"
 	yamlqueueconfig "github.com/uber/submitqueue/submitqueue/extension/queueconfig/yaml"
@@ -234,6 +235,9 @@ func run() error {
 		return fmt.Errorf("failed to open queue database: %w", err)
 	}
 	defer queueDB.Close()
+	if err := sqldb.ConfigureMaxOpenConnections(queueDB, os.Getenv("QUEUE_MYSQL_MAX_OPEN_CONNECTIONS")); err != nil {
+		return fmt.Errorf("configure queue database connection limit: %w", err)
+	}
 
 	// Initialize queue
 	mysqlQueue, err := queueMySQL.NewQueue(queueMySQL.Params{

service/submitqueue/orchestrator/server/BUILD.bazel

@@ -22,6 +22,7 @@ go_library(
         "//platform/extension/messagequeue:go_default_library",
         "//platform/extension/messagequeue/mysql:go_default_library",
         "//platform/http:go_default_library",
+        "//service/internal/sqldb:go_default_library",
         "//sqsim/adapter/buildrunner:go_default_library",
         "//sqsim/model:go_default_library",
         "//submitqueue/core/changeset:go_default_library",

service/submitqueue/orchestrator/server/main.go

@@ -42,6 +42,7 @@ import (
 	extqueue "github.com/uber/submitqueue/platform/extension/messagequeue"
 	queueMySQL "github.com/uber/submitqueue/platform/extension/messagequeue/mysql"
 	"github.com/uber/submitqueue/platform/http"
+	"github.com/uber/submitqueue/service/internal/sqldb"
 	simbuildrunner "github.com/uber/submitqueue/sqsim/adapter/buildrunner"
 	"github.com/uber/submitqueue/sqsim/model"
 	"github.com/uber/submitqueue/submitqueue/core/changeset"
@@ -196,6 +197,9 @@ func run() error {
 		return fmt.Errorf("failed to open queue database: %w", err)
 	}
 	defer queueDB.Close()
+	if err := sqldb.ConfigureMaxOpenConnections(queueDB, os.Getenv("QUEUE_MYSQL_MAX_OPEN_CONNECTIONS")); err != nil {
+		return fmt.Errorf("configure queue database connection limit: %w", err)
+	}
 
 	// Initialize queue
 	mysqlQueue, err := queueMySQL.NewQueue(queueMySQL.Params{

sqsim/runner/local.go

@@ -160,6 +160,7 @@ func newLocalStack(repoRoot, profileDir string, stdout, stderr io.Writer) *local
 			"REPO_ROOT="+repoRoot,
 			"SQSIM_PROFILE_DIR="+profileDir,
 			"SQSIM_SCENARIO_PATH=/sqsim/profile.json",
+			"QUEUE_MYSQL_MAX_OPEN_CONNECTIONS=32",
 		),
 	}
 }

sqsim/runner/local_test.go

@@ -15,6 +15,7 @@
 package runner
 
 import (
+	"slices"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -39,3 +40,8 @@ func TestFindRepoRootUsesWorkspaceEnvironment(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "/tmp/repo", root)
 }
+
+func TestLocalStackBoundsQueueDatabaseConnections(t *testing.T) {
+	stack := newLocalStack("/repo", "/profile", nil, nil)
+	assert.True(t, slices.Contains(stack.baseEnv, "QUEUE_MYSQL_MAX_OPEN_CONNECTIONS=32"))
+}

sqsim/scenarios/BUILD.bazel

@@ -3,7 +3,11 @@ load("@rules_go//go:def.bzl", "go_library", "go_test")
 go_library(
     name = "go_default_library",
     srcs = [
+        "failure.go",
         "happy_path.go",
+        "load.go",
+        "mixed.go",
+        "recovery.go",
         "registry.go",
     ],
     importpath = "github.com/uber/submitqueue/sqsim/scenarios",
@@ -14,7 +18,11 @@ go_library(
 go_test(
     name = "go_default_test",
     srcs = [
+        "failure_test.go",
         "happy_path_test.go",
+        "load_test.go",
+        "mixed_test.go",
+        "recovery_test.go",
         "registry_test.go",
     ],
     embed = [":go_default_library"],

sqsim/scenarios/failure.go

@@ -0,0 +1,51 @@
+// Copyright (c) 2026 Uber Technologies, Inc.
+//
+// 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.
+
+package scenarios
+
+import (
+	"time"
+
+	"github.com/uber/submitqueue/sqsim"
+)
+
+// BuildFailure returns a request whose Build Runner reports terminal failure.
+func BuildFailure() (sqsim.Scenario, error) {
+	behavior := sqsim.NewBehavior().
+		BuildRunner(sqsim.BuildFailedAfter(time.Second)).
+		MergeConflictCheck(sqsim.SuccessfulMergeConflictCheck()).
+		Merge(sqsim.SuccessfulMerge())
+	return singleErrorScenario(behavior)
+}
+
+// MergeConflict returns a request rejected by the dry-run mergeability check.
+func MergeConflict() (sqsim.Scenario, error) {
+	behavior := sqsim.NewBehavior().
+		BuildRunner(sqsim.SuccessfulBuildRunner()).
+		MergeConflictCheck(sqsim.ConflictingMergeConflictCheck()).
+		Merge(sqsim.SuccessfulMerge())
+	return singleErrorScenario(behavior)
+}
+
+func singleErrorScenario(behavior *sqsim.BehaviorBuilder) (sqsim.Scenario, error) {
+	return sqsim.NewScenario().
+		Timeout(30 * time.Second).
+		Land(
+			sqsim.NewLand("l1").
+				Queue("sqsim").
+				Behavior(behavior).
+				Expect(sqsim.RequestError),
+		).
+		Build()
+}

sqsim/scenarios/failure_test.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2026 Uber Technologies, Inc.
+//
+// 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.
+
+package scenarios
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/uber/submitqueue/sqsim"
+)
+
+func TestFailureScenariosExpectError(t *testing.T) {
+	tests := map[string]Builder{
+		"build failure":  BuildFailure,
+		"merge conflict": MergeConflict,
+	}
+	for name, build := range tests {
+		t.Run(name, func(t *testing.T) {
+			scenario, err := build()
+			require.NoError(t, err)
+			require.Len(t, scenario.Lands, 1)
+			assert.Equal(t, sqsim.RequestError, scenario.Lands[0].Expectation.Status)
+		})
+	}
+}