Rework BufferLogAppender buffer sizing logic to be more performant in the face of heavy throughput.

src/buffer-log-appender.ts

@@ -1,13 +1,44 @@
 import type { LogAppender } from './log-appender'
 import { LogLevel, type LogMessage } from './log-message'
+import { clamp } from './util'
+
+export interface BufferSizeBounds {
+  target: number
+  max: number
+}
 
 export class BufferLogAppender implements LogAppender {
   public threshold: LogLevel
   public buffer: LogMessage[]
-  public bufferMax?: number
 
-  constructor(buffer?: LogMessage[], threshold?: LogLevel) {
+  private _size?: BufferSizeBounds
-    this.buffer = buffer ?? []
+
+  public get size() {
+    return this._size === undefined ? undefined : { ...this._size }
+  }
+
+  public set size(s: {target: number, max?: number} | undefined) {
+    if (s === undefined) {
+      this._size = undefined
+    } else {
+      const target = clamp(s.target, { min: 1 })
+      this._size = {
+        target,
+        max: s.max === undefined
+          ? clamp(target * 1.2, { min: target + 1 })
+          : clamp(s.max, { min: target + 1 })
+      }
+    }
+  }
+
+  constructor(threshold?: LogLevel, size?: {target: number, max?: number}) {
+    if (size !== undefined && typeof size === 'object') {
+      this.size = size
+    } else {
+      this._size = { target: 1000, max: 1200 }
+    }
+
+    this.buffer = []
     this.threshold = threshold ?? LogLevel.ALL
   }
 
@@ -16,15 +47,32 @@ export class BufferLogAppender implements LogAppender {
 
     this.buffer.push(msg)
 
-    if (this.bufferMax !== undefined) {
+    if (this._size !== undefined) {
-      const max = Math.max(0, this.bufferMax)
+
-      while (this.buffer.length > max) {
+      if (this._size.max <= this._size.target) {
-        this.buffer.shift()
+        // This should be impossible, so if it happens, I want to know.
+        const oldSize = this.size
+        this.size = { target: this._size.target }
+        this.buffer.push({
+          scope: '@jdbernard/js-logging/buffer-log-appender.ts',
+          level: LogLevel.ERROR,
+          msg: {
+            msg: 'BufferLogAppender misconfigured: max size was not greater ' +
+            'than target size. Reconfiguring.',
+            oldSize,
+            newSize: this.size
+          },
+          ts: new Date()
+        })
+      }
+
+      if (this.buffer.length > this._size.max) {
+        this.buffer = this.buffer.slice(-this._size.target)
       }
     }
   }
 
   public clearBuffer(): void {
-    this.buffer.length = 0
+    this.buffer = []
   }
 }

src/util.ts

@@ -10,3 +10,14 @@ export function omit(
   }
   return result
 }
+
+export function clamp(
+    val: number,
+    bounds?: { min?: number, max?: number},
+    allowFloats?: boolean ): number {
+  let clamped = val
+  if (!allowFloats) clamped = Math.floor(clamped)
+  if (bounds?.min !== undefined) clamped = Math.max(bounds?.min, clamped)
+  if (bounds?.max !== undefined) clamped = Math.min(bounds?.max, clamped)
+  return clamped
+}