Support Min connection pool parameter #3009 (#3438)

* Support Min connection pool parameter #3009

* Remove extraneous change

* streamline code

Author: htrajan

packages/pg-pool/index.js

@@ -87,6 +87,7 @@ class Pool extends EventEmitter {
     }
 
     this.options.max = this.options.max || this.options.poolSize || 10
+    this.options.min = this.options.min || 0
     this.options.maxUses = this.options.maxUses || Infinity
     this.options.allowExitOnIdle = this.options.allowExitOnIdle || false
     this.options.maxLifetimeSeconds = this.options.maxLifetimeSeconds || 0
@@ -111,6 +112,10 @@ class Pool extends EventEmitter {
     return this._clients.length >= this.options.max
   }
 
+  _isAboveMin() {
+    return this._clients.length > this.options.min
+  }
+
   _pulseQueue() {
     this.log('pulse queue')
     if (this.ended) {
@@ -362,7 +367,7 @@ class Pool extends EventEmitter {
 
     // idle timeout
     let tid
-    if (this.options.idleTimeoutMillis) {
+    if (this.options.idleTimeoutMillis && this._isAboveMin()) {
       tid = setTimeout(() => {
         this.log('remove idle client')
         this._remove(client)

packages/pg-pool/test/sizing.js

@@ -55,4 +55,72 @@ describe('pool size of 1', () => {
       return yield pool.end()
     })
   )
+
+  it(
+    'does not remove clients when at or below min',
+    co.wrap(function* () {
+      const pool = new Pool({ max: 1, min: 1, idleTimeoutMillis: 10 })
+      const client = yield pool.connect()
+      client.release()
+      yield new Promise((resolve) => setTimeout(resolve, 20))
+      expect(pool.idleCount).to.equal(1)
+      return yield pool.end()
+    })
+  )
+
+  it(
+    'does remove clients when at or below min if maxUses is reached',
+    co.wrap(function* () {
+      const pool = new Pool({ max: 1, min: 1, idleTimeoutMillis: 10, maxUses: 1 })
+      const client = yield pool.connect()
+      client.release()
+      yield new Promise((resolve) => setTimeout(resolve, 20))
+      expect(pool.idleCount).to.equal(0)
+      return yield pool.end()
+    })
+  )
+
+  it(
+    'does remove clients when at or below min if maxLifetimeSeconds is reached',
+    co.wrap(function* () {
+      const pool = new Pool({ max: 1, min: 1, idleTimeoutMillis: 10, maxLifetimeSeconds: 1 })
+      const client = yield pool.connect()
+      client.release()
+      yield new Promise((resolve) => setTimeout(resolve, 1020))
+      expect(pool.idleCount).to.equal(0)
+      return yield pool.end()
+    })
+  )
+})
+
+describe('pool size of 2', () => {
+  it(
+    'does not remove clients when at or below min',
+    co.wrap(function* () {
+      const pool = new Pool({ max: 2, min: 2, idleTimeoutMillis: 10 })
+      const client = yield pool.connect()
+      const client2 = yield pool.connect()
+      client.release()
+      yield new Promise((resolve) => setTimeout(resolve, 20))
+      client2.release()
+      yield new Promise((resolve) => setTimeout(resolve, 20))
+      expect(pool.idleCount).to.equal(2)
+      return yield pool.end()
+    })
+  )
+
+  it(
+    'does remove clients when above min',
+    co.wrap(function* () {
+      const pool = new Pool({ max: 2, min: 1, idleTimeoutMillis: 10 })
+      const client = yield pool.connect()
+      const client2 = yield pool.connect()
+      client.release()
+      yield new Promise((resolve) => setTimeout(resolve, 20))
+      client2.release()
+      yield new Promise((resolve) => setTimeout(resolve, 20))
+      expect(pool.idleCount).to.equal(1)
+      return yield pool.end()
+    })
+  )
 })