https://blog.yaseerarafat.com/net-background-servi...

Question

https://blog.yaseerarafat.com/net-background-services-slower-hotter-costlier-8f1d6c8559f0 full detail

Answer 1

I can’t give you the full text of that page, because it’s a Medium “member-only story” and the content beyond the intro is not accessible from the public page view I can fetch. What I can do right now is:

pull out everything that’s publicly visible on that URL, and
give you a very detailed technical breakdown of the topic (why background services end up slower/hotter/costlier, and how to design them to stay predictable), backed by official .NET docs.

If you want a true “full detail” breakdown of that exact article, paste the article body here (or share a non-paywalled copy) and I’ll go section-by-section.

What’s publicly visible on that link

From the accessible excerpt, the article sets up this scenario: a “quiet” .NET Worker Service doing background tasks (queues, emails, sync, cleanup) suddenly causes massive CPU spikes, autoscaler churn, and a surprise cloud bill—arguing that the real culprit isn’t C#, but “unexamined assumptions.” (Medium)

The first assumption it calls out is:

“Background Services are just console apps with loops”—the typical while(true) + delay pattern that feels simple but hides operational pitfalls. (Medium)

That’s all that’s visible on the page without member access. (Medium)

The technical “why”: how background services get slower, hotter, and costlier

Below are the most common real failure modes behind that “it was fine until it wasn’t” story—grounded in how Hosted Services / BackgroundService actually behave.

1) Overlapping executions (silent concurrency explosion)

If you schedule work on a timer (or System.Threading.Timer) and the work sometimes takes longer than the interval, you can get overlapping runs. With System.Threading.Timer, callbacks can run concurrently; the callback “should be reentrant,” and it can execute simultaneously on multiple ThreadPool threads if the interval is shorter than the callback duration. (Microsoft Learn)

Even Microsoft’s hosted-services guidance warns that a timer doesn’t wait for prior executions to finish, so the naive timer approach may not fit many scenarios. (Microsoft Learn)

What that looks like in production

CPU ramps (more concurrent work than you think)
DB/Redis gets hammered (N overlapping polls)
memory rises (queues/results pile up)
autoscaler adds pods, which adds more pollers, which amplifies the problem

2) “Simple loop” polling that does constant work even when idle

Polling loops tend to do some work every tick (wakeups, queries, logs, allocations). If you have multiple instances (Kubernetes, App Service scale-out), you multiply that baseline cost by replica count.

Microsoft explicitly lists “polling a database looking for changes” as a background-task example—but that pattern needs careful design to avoid the scaling trap. (Microsoft Learn)

3) Scoped dependency lifetime mistakes (DbContext, HTTP handlers, etc.)

A hosted service is commonly registered as a singleton-ish long-lived service. No DI scope is created for a hosted service by default, so if you need scoped services, you must create a scope for each unit of work. (Microsoft Learn)

If you don’t:

you can accidentally hold onto scoped services forever (resource leaks)
you get incorrect behavior (stale contexts, stale caches)
you create contention and memory growth over time

4) Shutdown behavior and “stuck workers”

Hosted services are coordinated with app start/stop; StartAsync/StopAsync are part of the contract. (Microsoft Learn)
If you ignore the CancellationToken (or you Task.Delay(...) without the token), shutdown becomes slow or abrupt, which can cause retries, duplicates, and more compute.

Also worth knowing: in .NET 10, BackgroundService changed so all of ExecuteAsync runs on a background thread; previously the synchronous part (before the first await) ran on the main thread and could block startup. (Microsoft Learn)
That matters if your worker does heavy synchronous setup in ExecuteAsync.

5) Timer semantics you think you’re getting (but aren’t)

If you want periodic work without overlap, PeriodicTimer is often a better mental model because you explicitly await ticks. The docs note:

it’s intended for a single consumer (one wait in-flight at a time) (Microsoft Learn)
multiple ticks can be coalesced if they happen faster than you consume them (Microsoft Learn)

That coalescing can be a feature (prevents “catch-up storms”), but you need to be aware of it.

How to architect workers that stay linear, predictable, debuggable, and cheap

This is the practical “fix list” that typically eliminates the cost spikes:

A) Prefer event-driven work over polling

If you can, drive work from a queue/event stream instead of “check every N seconds.” When you must poll, add:

backoff when no work is found
jitter (to avoid thundering herd across replicas)
leader election / partitioning (so 10 pods don’t do the same scan)

B) Enforce explicit concurrency limits + backpressure

Make concurrency a knob:

max in-flight jobs
bounded channel/queue capacity
reject/park work when saturated (instead of “spawn tasks”)

C) One scope per unit of work

Create and dispose a scope each iteration (or each message) so scoped resources don’t accumulate. (Microsoft Learn)

D) Design around overlap by default

If your timer mechanism can overlap, assume it will.

If you use System.Threading.Timer, design callback to be reentrant and safe under concurrency (Microsoft Learn)
Or use an approach that naturally serializes the loop (example below)

E) Make shutdown boring

Honor stoppingToken everywhere. Also be aware you can configure shutdown timeouts (example shown in Microsoft’s microservices/host guidance). (Microsoft Learn)

Reference implementation skeleton (safe periodic worker)

csharp
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using System.Threading;

public interface ICatalogSyncJob
{
    Task RunOnceAsync(CancellationToken ct);
}

public sealed class CatalogSyncWorker : BackgroundService
{
    private readonly IServiceScopeFactory _scopeFactory;
    private readonly ILogger<CatalogSyncWorker> _logger;
    private readonly PeriodicTimer _timer = new(TimeSpan.FromSeconds(10));

    public CatalogSyncWorker(IServiceScopeFactory scopeFactory, ILogger<CatalogSyncWorker> logger)
    {
        _scopeFactory = scopeFactory;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (await _timer.WaitForNextTickAsync(stoppingToken))
        {
            try
            {
                await using var scope = _scopeFactory.CreateAsyncScope();
                var job = scope.ServiceProvider.GetRequiredService<ICatalogSyncJob>();

                await job.RunOnceAsync(stoppingToken);
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                // normal shutdown
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Background job failed; backing off");
                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken);
            }
        }
    }

    public override void Dispose()
    {
        _timer.Dispose();
        base.Dispose();
    }
}

Why this shape matches the official guidance:

PeriodicTimer is an async “wait for tick” primitive (Microsoft Learn)
scoped services are created via an explicit scope, because hosted services don’t get one by default (Microsoft Learn)

If you want “full detail of the article” specifically

Paste the article text here (even in chunks), and I’ll:

summarize each section,
extract the author’s specific claims and examples,
translate them into a concrete checklist + code patterns tailored to your situation.

Answer 2

Sure — before we dive in, quick check so I explain it at the right level:

Are you trading/investing (stocks/crypto/forex), and on what timeframe (1m/5m/day)?

Answer 3

Nice — swing trading is a great timeframe for “volume + candlesticks” because you can actually see who’s in control (buyers vs sellers) without the noise of 1-minute charts.

Let’s build this in a way you can use tomorrow.

Step 1: What volume is really telling you

Think of volume as the “effort” behind the candle.

Big candle + big volume = strong conviction (institutions can be involved).
Big candle + low volume = suspect move (often easier to reverse).
Small candle + big volume = battle/absorption (important!).

Step 2: The 4 highest-value candle+volume “stories” for swing trades

1) Breakout that’s real vs fake

Real breakout: price breaks resistance AND volume is higher than recent average → odds improve that the move follows through.
Fake breakout: price pokes above resistance but volume is meh → often reverses back into the range.

Your move: On the breakout candle, compare volume to the last ~20 bars (mentally: “is it clearly above normal?”).

2) “Stopping volume” after a selloff (possible bottom)

Look for:

Several red candles down (downtrend),
then a big volume spike on a candle with a long lower wick (hammer / rejection).

Story: sellers dumped hard, but buyers absorbed it and pushed price back up off the lows.

Your move: Mark the low of that wick. If price holds above it over the next few candles, that low becomes a key risk level.

3) “No demand / no supply” candles (quiet tells)

Up candle with low volume near resistance = no demand (buyers not committing).
Down candle with low volume near support = no supply (selling pressure drying up).

Story: The move is weak; market may be setting up for the opposite direction.

Your move: When you see low-volume drift into a key level, wait for the next strong candle+volume to confirm direction.

4) High volume but price goes nowhere (absorption = big clue)

Candle has:

relatively small body (or lots of wicks),
very high volume.

Story: heavy buying and selling occurred, but price didn’t progress → one side is absorbing the other.

If this happens at support after a drop, buyers may be absorbing sells.
If at resistance after a rise, sellers may be absorbing buys.

Your move: Treat that zone like a “wall.” A clean break later (with volume) is meaningful.

Step 3: A simple swing-trader routine (fast + practical)

Draw support/resistance (recent swing highs/lows).
Ask: Are we trending or ranging?
Only care about volume when price is:
- breaking a level, or
- rejecting a level, or
- stalling at a level.
Confirmation rule: “Big move needs big volume.”
Risk rule: put your invalidation beyond the wick/level that created the signal.

Mini practice (one question)

Imagine price breaks above resistance with a strong green candle, but volume is lower than the last 10–20 candles.

As a swing trader, what does that suggest to you: strong breakout or possible fakeout?

Answer 4

Here’s a swing-trader “invalidation process chart” you can use with candlesticks + volume. The goal is simple: define exactly what has to happen for your idea to be wrong, and then act fast when it does.

Invalidation process chart (flow)

text
START
  │
  ├─► 1) Identify setup type
  │        A) Breakout     B) Pullback (trend)     C) Reversal at S/R
  │
  ├─► 2) Write the thesis in 1 sentence
  │        "If price holds above/below X, it should move toward Y."
  │
  ├─► 3) Mark the "line in the sand" (price level)
  │        - Breakout: prior resistance/support + breakout candle structure
  │        - Pullback: higher low / lower high area or moving average zone
  │        - Reversal: the wick-low (for long) or wick-high (for short)
  │
  ├─► 4) Define HARD invalidation (exit no matter what)
  │        Usually: a candle CLOSE beyond your line in the sand
  │        (not just an intraday wick), OR the wick is broken if using wick-based stop.
  │
  ├─► 5) Define VOLUME invalidation (the "uh-oh" signal)
  │        "If price does the wrong thing WITH high volume → exit faster."
  │
  ├─► 6) Add TIME invalidation (prevents slow bleeding)
  │        "If no progress after N candles/days → exit or reduce."
  │
  └─► 7) Execute: either HOLD, REDUCE, or EXIT based on which invalidation triggers
END

The 3 most common swing setups + exact invalidation rules

A) Breakout long (above resistance)

Entry idea: price breaks resistance and continues.

Hard invalidation (classic):

Daily close back below breakout level (old resistance)
or close back inside the prior range.

Volume invalidation (faster exit):

Price closes back below breakout level on high/above-average volume
→ that’s often “failed breakout / bull trap.”

Extra (good filter):

If the breakout candle is strong but volume is weak, you can require a successful retest before sizing up.

B) Pullback long (uptrend continuation)

Entry idea: trend is up; pullback is a reset before the next leg.

Hard invalidation:

The pullback makes a lower low below the swing low you’re leaning on
(your “higher-low” fails).

Volume invalidation:

The down candles during the pullback start printing bigger volume than the prior up candles
→ selling pressure is dominating, pullback may be turning into reversal.

Candlestick invalidation clue:

A clean bearish close through support with little wick (no rejection) is more concerning than a wicky probe.

C) Reversal long at support (downtrend exhaust / bounce)

Entry idea: sellers are exhausting at support; buyers absorb.

Hard invalidation (most common):

Price breaks the reversal wick low (the “hammer low” / flush low).
That wick is the whole point of the setup.

Volume invalidation:

A breakdown below support with high volume after your reversal signal
→ likely not “exhaustion,” likely “continuation.”

Time invalidation (important on reversals):

If the bounce doesn’t show follow-through within a few candles (2–5 on the daily), odds drop.

“Soft vs hard” invalidation (so you don’t overreact to noise)

Use a two-tier system:

Soft invalidation (reduce / tighten):
- A close against your thesis, but on low volume
- Or choppy candles (indecision) where you expected clean trend
Hard invalidation (exit):
- A close beyond your line in the sand
- Or the wrong move happens with high volume (strong conviction against you)

Quick checklist you can screenshot

Before entry

What level proves me wrong? (write the price)
Is my stop based on a close or a wick?
What volume behavior should I see if I’m right?
What’s my time stop? (ex: “if not moving in 5 trading days, I’m out”)

After entry

Wrong-direction close near my invalidation level?
Wrong-direction move with high volume?
No progress by time limit?

If “yes” → reduce/exit per your rules.

If you tell me what chart timeframe you use for swing trading (daily only vs 4H + daily), I’ll tailor the chart into exact numbers like: “invalidate on a daily close under X” vs “invalidate on 4H close under X, but only exit fully on daily close.”

問題

思考

Clarifying the Response Structure

Unpacking Assumptions About Background Services

Root Causes of Spikes and Slowdowns

Root Causes of Performance Issues

Fixing Background Service Patterns

回答