Cheat sheets

Register < 1 ns · L1 ~1 ns · L3 ~10–20 ns · RAM ~100 ns · SSD ~50 µs · HDD ~5 ms · same-DC network ~0.5 ms · cross-continent ~150 ms.

Stack: per thread, frames, locals, fast, auto-freed, ~1 MB, overflow on deep recursion. Heap: shared, objects, GC-managed in .NET, leaks = still referenced.

Process = own address space, isolated. Thread = path inside a process, shares heap, own stack. Context switch = save/restore thread state.

Race → lock / Interlocked / immutability. Deadlock → same lock order, short locks, timeouts, no .Result. Starvation → fair scheduling, async.

C# → Roslyn → IL → JIT (tiered) → machine code; OS loads process, CLR manages memory with GC; I/O via system calls.

O(1) < O(log n) < O(n) < O(n log n) < O(n²) < O(2ⁿ) < O(n!). For n = 10⁶: O(n log n) OK, O(n²) not.

Index access → array/List · key lookup → Dictionary/HashSet · LIFO → Stack · FIFO → Queue · min/max fast → PriorityQueue · sorted + range → SortedDictionary / B-tree index · prefix → Trie · relationships → graph adjacency list.

Merge: n log n always, stable, O(n) space. Quick: n log n avg, n² worst, in place. Heap: n log n, O(1) space. Insertion: great for tiny/nearly sorted. .NET Array.Sort = introsort (unstable); LINQ OrderBy = stable.

Two pointers · sliding window · prefix sums · binary search (also on the answer) · BFS (shortest unweighted) · DFS/backtracking · heap for top-K · hash map for counting/lookups · DP for overlapping subproblems · greedy when locally optimal is globally optimal.

Clarify → examples → brute force + Big-O → optimise → code → test edge cases → state time/space.

*amortised/average

Reverse string · palindrome · anagram · char count · first unique char · reverse words · Fibonacci · prime · factorial · Armstrong · FizzBuzz · swap · second largest · duplicates · missing number · move zeros · rotate array · merge sorted arrays · two sum · Kadane · valid parentheses · reverse linked list · cycle detection · binary search · bubble/quick/merge sort · tree height/BFS · LRU cache.

Clarify → examples → brute force + Big-O → optimise → code → dry-run → edge cases (empty, one, duplicates, negatives, overflow) → final Big-O.

URL → cache/HSTS → DNS → TCP (or QUIC) → TLS → HTTP request → CDN/WAF → load balancer → web server → app → DB → response → DOM/CSSOM → layout → paint.

L7 HTTP/DNS · L4 TCP/UDP (ports) · L3 IP (routers) · L2 Ethernet/Wi-Fi (switches, MAC) · L1 physical. L4 vs L7 load balancing.

Ports 80/443/22/3389/1433/6379/53 · private ranges 10/8, 172.16/12, 192.168/16 · /24 = 256 addresses · TLS 1.3 = 1 RTT · TTL 300 s before migrations.

Shared → VPS/VM (IaaS) → PaaS (App Service) → containers (Container Apps/AKS) → serverless (Functions); static SPA → Static Web Apps/CDN.

nslookup/dig · ping/tracert · Test-NetConnection -Port · curl -v · DevTools Network timing · SSL Labs · IIS stdout log + Event Viewer · App Insights.

Requirements → estimation → API → data model → diagram → deep dive → bottlenecks/failures → trade-offs.

1M/day ≈ 12/s · peak 2–10× · day ≈ 10⁵ s · 99.9 % ≈ 8.8 h/yr down · 99.99 % ≈ 53 min/yr.

DNS/CDN · load balancer · API gateway · stateless services · cache (Redis) · SQL + replicas · NoSQL · object storage · queue/stream · search index · rate limiter · monitoring.

Indexes → caching → read replicas → vertical scale → partitioning → sharding (consistent hashing) → multi-region.

Consistency vs availability · latency vs consistency · push vs pull · SQL vs NoSQL · sync vs async · cost vs redundancy · simplicity (monolith) vs independence (microservices).

Requirements → use cases → nouns/verbs → relationships → class diagram → SOLID + patterns → code core flow → concurrency, edge cases, tests, tables.

Varying rule → Strategy · lifecycle states → State · object creation → Factory/Builder · notify many → Observer · add features → Decorator · pass along handlers → Chain of Responsibility · undo/queue requests → Command · simple front door → Facade · one instance → DI singleton.

+ public - private # protected · ▷ inheritance · ┈▷ interface · ◆ composition · ◇ aggregation · multiplicities 1, 0..1, , 1...

Parking lot · library · elevator · vending machine · ATM (chain of note dispensers) · LRU cache · rate limiter · Splitwise · movie booking (seat locks) · snake & ladder · chess · hotel booking · food delivery.

Lock critical sections · atomic ops (Interlocked, ConcurrentDictionary.TryAdd) · optimistic concurrency (row version) · unique constraints · distributed locks with TTL · idempotent operations.

Value types are copied on assignment; reference types share one object.

• const vs readonly: compile-time and copied into callers vs set once at runtime.
• is vs as: is tests a type/pattern (bool); as casts or gives null.
• ref vs out vs in: read/write vs must assign vs read-only.
• abstract vs virtual: no body, must override vs has a body, may override.
• sealed: can't inherit (class) or override further (method).
• new modifier: hides a base member (no polymorphism).
• static class: can't be instantiated; only static members.
• throw; keeps the stack trace; throw ex; loses it.

• async Task / Task<T>; async void only for event handlers.
• Never .Result / .Wait() — async all the way.
• Independent calls: await Task.WhenAll(...).
• Pass CancellationToken.
• CPU-bound: Task.Run / Parallel; I/O-bound: just await.
• Use SemaphoreSlim (not lock) around await.

• GC generations 0/1/2; LOH ≥ 85,000 bytes.
• using / await using for IDisposable / IAsyncDisposable.
• Finaliser = last-resort safety net; GC.SuppressFinalize.
• Leaks: static collections, events not unsubscribed, HttpClient per call, unbounded caches.
• Low-allocation code: Span<T>, ArrayPool, StringBuilder, stackalloc.

1. Value vs reference types (with the stack/heap nuance).
2. string immutability + StringBuilder.
3. IEnumerable vs IQueryable.
4. async/await doesn't create threads; no .Result.
5. IDisposable + using + GC generations.
6. Delegates vs events.

int[] fixed · int[,] rectangular · int[][] jagged · List<T> growable · Dictionary<K,V> key lookup (TryGetValue) · HashSet<T> unique · SortedList/SortedDictionary ordered keys · Stack<T> LIFO · Queue<T> FIFO · PriorityQueue<T,P> · ArrayList/Hashtable = legacy (boxing, no type safety) · (int, string) ValueTuple for quick multi-returns.

Func returns · Action void · Predicate bool · += multicast · out T covariance, in T contravariance · throw; not throw ex; · custom exception = derive Exception + 3 constructors · File.ReadLines for big files · always using/await using streams · Path.Combine for paths.

Dim x As T → T x · Sub/Function → void/method · Me/MyBase → this/base · Shared/Module → static · Nothing → null · Inherits/Implements → : · MustInherit/MustOverride → abstract · Overridable/Overrides → virtual/override · NotInheritable → sealed · Friend → internal · Shadows → new.

= equality · <> not equal · & concat · \ int division · Mod · ^ power · AndAlso/OrElse short-circuit · Is/IsNot reference · If(c,a,b) ternary · If(x,y) null-coalesce.

Option Strict On · Option Explicit On · Option Infer On · arrays declare upper bound · (Of T) generics · arr(i) indexing.

Event + RaiseEvent · WithEvents + Handles · AddHandler/RemoveHandler + AddressOf.

Option Strict first → tests → extract logic to libraries → convert libraries → rebuild UI in ASP.NET Core (strangler) → watch 1-based string functions and integer division.

Source → Roslyn → assembly (IL + metadata + manifest) → host starts CLR → loader + type loader → JIT (tier 0 → tier 1 + PGO) → native code → GC manages heap.

Framework 1.0 (2002) → 2.0 generics → 3.5 LINQ → 4.0 TPL → 4.5 async → 4.8 last (4.8.1 ARM64). Core 1.0 (2016) → 2.1 LTS → 3.1 LTS. .NET 5 (2020) → 6 LTS → 7 → 8 LTS → 9 → 10 LTS (2025). Even = LTS 3 yrs, odd = STS 2 yrs.

Gen 0 → 1 → 2; LOH ≥ 85,000 bytes (not compacted); POH for pinned; Workstation vs Server (+ background, DATAS); roots = stacks, statics, handles; finalizers delay collection; never GC.Collect() in normal code.

using/await using everything disposable · SafeHandle instead of finalizers · Dispose(bool) + GC.SuppressFinalize for the full pattern · dispose what you own only.

dotnet-counters (live) · dotnet-gcdump (heap) · dotnet-dump analyze (dumpheap -stat, gcroot) · dotnet-trace (CPU/events) · BenchmarkDotNet MemoryDiagnoser.

• Encapsulation — private data, public methods that guard rules.
• Abstraction — interfaces/abstract classes expose what, hide how.
• Inheritance — Derived : Base reuses and extends ("is-a").
• Polymorphism — overloading (compile time) and overriding (runtime).

• Association: uses (independent lifetimes)
• Aggregation: has-a (part survives)
• Composition: owns-a (part dies with whole)
• Inheritance: is-a
• Prefer composition; inherit only for true substitutable "is-a".

Static field initialisers → static ctor (once) → instance field initialisers (derived, then base) → base ctor body → derived ctor body.

• Override Equals(object), implement IEquatable<T>, override GetHashCode with HashCode.Combine.
• Or use record for value equality for free.

Never inject scoped into singleton → use IServiceScopeFactory.

• DRY — one source of truth for knowledge.
• KISS — simplest thing that works.
• YAGNI — don't build for imaginary futures.
• SoC — separate UI / business / data.
• Composition over inheritance.
• Law of Demeter — no a.B.C.D chains.

• SRP: "A class should have one reason to change — one actor it serves."
• OCP: "Add new behaviour by adding classes, not by editing tested ones."
• LSP: "A subclass must work anywhere its base class is expected — no surprises."
• ISP: "Don't force clients to depend on methods they don't use."
• DIP: "High-level policy depends on abstractions; details plug in through DI."
• Balance: "I apply SOLID where change is likely; for simple, stable code I keep it simple."

• Repository + UoW — data access abstraction + one transaction.
• CQRS — separate reads and writes.
• Outbox — event + data in the same transaction.
• Saga — distributed transaction with compensation.
• Retry / Circuit Breaker / Timeout / Bulkhead — resilience (AddStandardResilienceHandler).
• Options — typed config: IOptions / IOptionsSnapshot / IOptionsMonitor.
• Strangler Fig — replace a legacy system piece by piece.
• API Gateway / BFF — single entry point per client type.

Problem → pattern name → how it works (2 lines) → code shape (interface + classes) → where you used it → trade-off.

SqlConnection · SqlCommand · SqlParameter · SqlDataReader · SqlDataAdapter · DataSet/DataTable/DataView · SqlTransaction · SqlBulkCopy · SqlCommandBuilder.

Server · Database · Integrated Security=True / User Id+Password / Authentication=Active Directory Default · Encrypt=True · TrustServerCertificate=True (dev) · Max Pool Size · Connect Timeout · MultipleActiveResultSets · Application Name.

Query<T> · QueryFirstOrDefault<T> · QuerySingle<T> · Execute · ExecuteScalar<T> · QueryMultiple · multi-mapping splitOn · IN @Ids · commandType: CommandType.StoredProcedure · pass transaction.

Always parameterise · explicit SqlDbType + size · using/await using · open late, close early · pool max 100 · Encrypt=True default in SqlClient 4+ · SqlBulkCopy for bulk · TVP for lists · retry transient errors.

Deferred: returns IEnumerable/IQueryable. Immediate: returns a value, collection or element.

Delegates, in memory vs expression trees, translated to SQL. Keep IQueryable until ToListAsync().

ToList() too early · multiple enumeration · Count() > 0 instead of Any() · First without OrderBy · N+1 with lazy loading · untranslatable methods in IQueryable · list.Contains in loops (use HashSet).

Detached · Added → INSERT · Unchanged · Modified → UPDATE · Deleted → DELETE.

Include/ThenInclude (eager) · Entry().Collection().Load() (explicit) · lazy proxies (avoid) · Select projection (best for reads) · AsSplitQuery.

AsNoTracking · Select DTOs · AnyAsync · paginate Skip/Take · ToQueryString() · FromSql($"") · SqlQuery<T> · ExecuteUpdate/Delete · EF.CompileAsyncQuery · IgnoreQueryFilters.

Fluent API > Data Annotations > Conventions. Use IEntityTypeConfiguration<T>.

HasOne().WithMany().HasForeignKey().OnDelete() · HasOne().WithOne().HasForeignKey<T>() · many-to-many via skip navigations · owned/complex types · TPH (default) / TPT / TPC.

[Timestamp] byte[] RowVersion → DbUpdateConcurrencyException → 409 · SaveChanges = one transaction · BeginTransactionAsync for multiple saves · execution strategy with retries.

Scoped · short-lived · not thread-safe · IDbContextFactory for background/parallel · AddDbContextPool for throughput.

Query<T> · QueryFirst(OrDefault)<T> · QuerySingle(OrDefault)<T> · Execute · ExecuteScalar<T> · QueryMultiple · QueryUnbufferedAsync · all with Async versions and CommandDefinition for timeout/cancellation.

Anonymous object new { Id = id } · DynamicParameters for types/size/direction · IN @ids with a collection · DbString { IsAnsi = true } for VARCHAR · never interpolate values.

Multi-mapping Query<A,B,A>(sql, map, splitOn:) · stored procs commandType: CommandType.StoredProcedure · outputs p.Get<T>() · transactions pass tx · TVP AsTableValuedParameter · SqlBulkCopy for bulk · SqlMapper.TypeHandler<T>.

Connection factory (singleton) · repositories (scoped) · open late, dispose early · unit of work for multi-step transactions · EF Core for writes + Dapper for reads is common.

Only needed columns · server paging · correct parameter types · fewer round trips · read the execution plan.

PreInit → Init → InitComplete → (LoadViewState, LoadPostData) → PreLoad → Load → control events → LoadComplete → PreRender → SaveStateComplete → Render → Unload.

BeginRequest → Authenticate → Authorize → ResolveRequestCache → AcquireRequestState → PreRequestHandlerExecute → handler (Page) → PostRequestHandlerExecute → ReleaseRequestState → UpdateRequestCache → EndRequest.

Page: ViewState/ControlState/hidden field · request: query string · browser: cookies · user: Session (InProc/StateServer/SQL/Redis) · all users: Application/Cache.

App_Code · App_Data · App_Start · App_Themes · App_GlobalResources · bin · .aspx + .aspx.cs + .designer.cs · .master · .ascx · .ashx · Global.asax · Web.config (+ transforms).

try/catch → Page_Error → Application_Error (log) → customErrors/httpErrors (friendly pages) · never debug="true" or customErrors="Off" in production.

UrlRoutingModule → MvcRouteHandler → MvcHandler → ControllerFactory → ActionInvoker → authN/authZ filters → model binding → action filters → action → result filters → ActionResult.ExecuteResult → view engine → response.

App_Start (Route/Filter/Bundle/Identity config) · Controllers · Models · Views (+Shared, _ViewStart, web.config) · Areas · Content · Scripts · Global.asax · Web.config.

Strongly typed model > ViewData/ViewBag (this request) · TempData (next request) · Session (user).

Authentication → Authorization → Action → Result · Exception · global/controller/action scope.

Global.asax → Program.cs · modules → middleware · child actions → view components · HTML helpers → tag helpers · DependencyResolver → built-in DI · separate Web API → unified controllers.

New major every November · even = LTS (3 yrs) · odd = STS (2 yrs).

CLR (runtime) · IL (intermediate code) · JIT (runtime compile) · tiered compilation + Dynamic PGO · R2R (precompiled) · Native AOT · CTS/CLS · BCL · GC Gen 0/1/2 + LOH (≥ 85 KB) + POH · Workstation vs Server GC.

appsettings.json → appsettings.{Env}.json → user secrets (Dev) → env vars (A__B) → command line.

IOptions (singleton, once) · IOptionsSnapshot (scoped, per request) · IOptionsMonitor (singleton, live + OnChange).

Transient · Scoped (per request) · Singleton · Keyed (.NET 8) · no scoped-in-singleton.

Middleware → Routing → Controller (DI) → Authorization filter → Resource filter → Model binding → Validation → Action filter → Action → Action filter → Result filter → View render → Result filter → Response. Exception filters wrap the action/result stages.

View · PartialView · ViewComponent · Json · Content · File · Redirect · RedirectToAction · LocalRedirect · NotFound · BadRequest · Unauthorized · Forbid · StatusCode.

[FromQuery] [FromRoute] [FromForm] [FromBody] [FromHeader] [FromServices] [Bind("A,B")] [BindProperty] (Razor Pages).

[Required] [StringLength] [MaxLength] [Range] [EmailAddress] [Phone] [Url] [Compare("Password")] [RegularExpression] [Remote] · custom ValidationAttribute · IValidatableObject.

Antiforgery on POST forms · [Authorize] + fallback policy · ownership checks (IDOR) · LocalRedirect for returnUrl · no Html.Raw on user input · HTTPS + HSTS · secure cookies · view models (no over-posting).

200 · 201 · 202 · 204 · 304 · 400 · 401 (who are you?) · 403 (not allowed) · 404 · 409 · 412 · 415 · 422 · 429 · 500 · 502 · 503 · 504.

MapGet/MapPost/MapPut/MapPatch/MapDelete · MapGroup · TypedResults · Results<Ok<T>, NotFound> · [AsParameters] · AddEndpointFilter · RequireAuthorization · RequireRateLimiting · WithTags/WithName.

JWT = header.payload.signature (signed, not encrypted) · validate iss/aud/exp/signature · Auth Code + PKCE / Client Credentials · CORS ≠ auth · rate limit · HTTPS/HSTS · Key Vault.

HTTP headers/ETag · Output cache · IMemoryCache · IDistributedCache (Redis) · HybridCache (.NET 9).

DTOs not entities · ProblemDetails for errors · CancellationToken everywhere · IHttpClientFactory · pagination with max size · version before breaking · idempotency keys for payments.

Validate early · catch specific · throw; · wrap with inner · using for cleanup · no empty catch · no exceptions for flow · global handler at boundaries · log once with correlation id · friendly messages, no internals.

AddProblemDetails + AddExceptionHandler<T> + UseExceptionHandler() · UseStatusCodePages(WithReExecute) · exception filters for MVC · [ApiController] 400s · developer page only in Development.

Web Forms: try/catch → Page_Error → Application_Error → customErrors/httpErrors · MVC 5: OnException → [HandleError]/IExceptionFilter → Application_Error · Web API 2: IExceptionHandler/IExceptionLogger.

Validation 400 · auth 401/403 · not found 404 · conflict/duplicate/concurrency 409 · business rule 422 · rate limit 429 · bug/unknown 500 · dependency down 502/503 · timeout 504.

await rethrows first exception · WhenAll → check InnerExceptions · avoid async void · BackgroundService: try/catch per iteration · AppDomain.UnhandledException / TaskScheduler.UnobservedTaskException for last-chance logging.

Trace < Debug < Information < Warning < Error < Critical · production default Information, framework categories Warning.

Message templates with named properties · LogError(ex, ...) with the exception · scopes/enrichers for context · correlation/trace ids · JSON to stdout in containers · central store + retention + alerts.

Interpolate log messages · log secrets/PII · log the same exception at every layer · log inside tight loops · block requests on log writes.

ILogger (abstraction) · Serilog (structured, sinks, enrichers, UseSerilogRequestLogging) · NLog (nlog.config targets/rules) · log4net (legacy XML appenders) · ELMAH (Framework errors) · OpenTelemetry (logs + traces + metrics).

ILoggerProvider + ILogger · bounded Channel queue · background batch writer · never throw · flush on Dispose · builder.Logging.AddProvider(...).

Web Forms: user control (one app) → custom/composite control (many apps) · MVC 5: partial/display template → HTML helper → child action · Core: partial → tag helper → view component → Razor Class Library · Blazor: component (+ library) · WinForms/WPF: UserControl → custom control.

WebControl + RenderContents · ViewState-backed properties · CompositeControl.CreateChildControls + INamingContainer · events · ControlState · [ToolboxData].

Tag helper: [HtmlTargetElement], Process(Async), @addTagHelper · View component: InvokeAsync, Views/Shared/Components/Name/Default.cshtml, <vc:name>.

[Parameter] · EventCallback · RenderFragment / RenderFragment<T> · @typeparam · @bind-Value = Value + ValueChanged · CascadingValue · lifecycle methods · @key · Virtualize.

Small API · data in, events out · encode output · accessible · styleable · tested · versioned.

3-tier/N-layer (UI → BLL → DAL) · Onion/Clean/Hexagonal (domain centre, dependencies inward) · Vertical Slice (per feature) · Modular monolith (modules + schemas) · Microservices.

Domain (entities, value objects, events) ← Application (use cases, interfaces, DTOs, validation) ← Infrastructure (EF, email, files) ; Api = composition root (controllers, middleware, Program.cs).

src/ · tests/ · docs/ (ADRs) · deploy/ · Directory.Build.props · Directory.Packages.props · global.json · .editorconfig · .sln/.slnx.

Exceptions & auth → Api · validation & transactions & mapping → Application · invariants → Domain · persistence & external services → Infrastructure · logging → everywhere via ILogger.

Small CRUD → simple single project · rich domain → Clean · many independent features → Vertical Slice · many teams → modular monolith · independent scaling/deploys → microservices · write an ADR, enforce with architecture tests.

• Intention-revealing names; verbs for methods, nouns for classes.
• Functions: small, one thing, ≤ 3 params, guard clauses.
• No magic numbers; no commented-out code; comments explain why.
• Exceptions for exceptional cases; global handler; structured logs.
• Boy Scout rule; small PRs; consistent formatting.

• AAA: Arrange · Act · Assert. FIRST tests.
• xUnit: [Fact], [Theory] + [InlineData]; ctor = setup, Dispose = teardown; IClassFixture<T>.
• Moq: new Mock<T>(), .Setup(...).ReturnsAsync(...), .Verify(..., Times.Once).
• Doubles: dummy, stub, fake, mock, spy.
• Pyramid: unit ≫ integration ≫ E2E.
• WebApplicationFactory<Program> for API tests; Testcontainers for real SQL Server.
• TimeProvider / FakeTimeProvider for time.

Long method → Extract Method · God class → Extract Class · Switch on type → Polymorphism · Duplicates → Extract/DRY · Long params → Parameter Object · Primitive obsession → Value Object · Feature envy → Move Method.

Parameterised SQL · [Authorize] + ownership checks · HTTPS/HSTS · Identity password hashing · Antiforgery · Razor encoding · Key Vault for secrets · updated packages · no secrets/PII in logs.

Modular monolith by default → extract a service only for independent scaling, release cadence, ownership or technology. Split by business capability (bounded context), never by technical layer.

Local transaction per aggregate · saga (choreography/orchestration) with compensations · transactional outbox · idempotent consumer / inbox · idempotency keys · eventual consistency shown in UI.

Timeout · retry + backoff + jitter (idempotent only) · circuit breaker · bulkhead · fallback · health checks (live/ready) · DLQ. .NET: AddStandardResilienceHandler().

Logs + metrics + traces via OpenTelemetry; correlation/trace id everywhere; golden signals: latency, traffic, errors, saturation; .NET Aspire dashboard locally, App Insights/Grafana in production.

Requirements → estimates → API → data model → diagram → deep dive → bottlenecks & failures → trade-offs. Always mention cache, queue, replicas, idempotency and monitoring.

FROM → ON → JOIN → WHERE → GROUP BY → HAVING → SELECT → DISTINCT → ORDER BY → TOP/OFFSET.

INNER · LEFT · RIGHT · FULL · CROSS · SELF · CROSS APPLY · OUTER APPLY · anti-join (LEFT JOIN ... WHERE b.Id IS NULL or NOT EXISTS).

Nth highest salary (DENSE_RANK) · duplicates (GROUP BY HAVING) · delete duplicates (CTE + ROW_NUMBER) · employee–manager (self join) · org chart (recursive CTE) · top N per group · running total · customers without orders (NOT EXISTS) · pivot (CASE/PIVOT) · upsert (MERGE).

One clustered (narrow, unique, increasing) · non-clustered for selective filters · equality columns first, then range · INCLUDE to cover · filtered for subsets · columnstore for analytics · SARGable predicates · every index costs writes.

READ UNCOMMITTED → READ COMMITTED (default) → REPEATABLE READ → SERIALIZABLE; SNAPSHOT and RCSI use row versions (readers don't block writers).

GETDATE() SYSUTCDATETIME() DATEADD DATEDIFF EOMONTH FORMAT CAST/CONVERT/TRY_CONVERT ISNULL/COALESCE/NULLIF IIF CHOOSE LEN SUBSTRING CHARINDEX REPLACE TRIM STRING_AGG STRING_SPLIT CONCAT_WS JSON_VALUE OPENJSON @@ROWCOUNT SCOPE_IDENTITY() NEWID() GREATEST/LEAST (2022).

SET STATISTICS IO, TIME ON · actual execution plan · Query Store · sys.dm_exec_requests · sys.dm_exec_query_stats · sys.dm_db_index_usage_stats · sys.dm_db_missing_index_details · sp_WhoIsActive · Extended Events system_health for deadlocks.

Protocol (TDS) → Relational engine (parse, bind, optimise, execute, plan cache) → Storage engine (access methods, buffer pool, locks, log) → SQLOS (schedulers, workers, waits).

Page 8 KB · extent 64 KB · GAM/SGAM/PFS/IAM · heap (RID) vs clustered B+ tree (rows at leaf) · nonclustered (key + locator) · INCLUDE = covering · good clustered key: narrow, unique, static, increasing.

Statistics (200-step histogram) → cardinality estimates → cheapest plan → plan cache · SARGable predicates · parameter sniffing fixes: index, RECOMPILE, OPTIMIZE FOR, Query Store forcing, PSP (2022).

Right to left · seek vs scan · key lookup · nested loops (small outer) · merge (sorted) · hash (large unsorted, memory) · spills · implicit conversions · estimated vs actual rows.

WAL + LSN · commit = log hardened · checkpoint · recovery: analysis, redo, undo · ADR · recovery models SIMPLE/FULL/BULK_LOGGED · log backups in FULL.

Locks S/U/X/intent/schema · escalation ~5,000 locks · latches = internal · isolation RU/RC/RR/SER + RCSI/SNAPSHOT (version store) · deadlock = error 1205 → retry + same access order + short transactions.

PAGEIOLATCH (disk reads) · LCK_M (blocking) · WRITELOG (log disk) · CXPACKET (parallelism) · SOS_SCHEDULER_YIELD (CPU) · RESOURCE_SEMAPHORE (memory grants) · ASYNC_NETWORK_IO (client).

ETL: transform before load (SSIS). ELT: load raw, transform in the warehouse (ADF/Fabric + SQL/dbt/Spark).

Full (truncate + reload) · Incremental (watermark, rowversion, CDC, Change Tracking, hash) · Upsert (MERGE) · Deletes (soft delete, CDC, full compare).

Fact (measures at a grain) + Dimensions (descriptive) · Star (denormalised) vs Snowflake (normalised dims) · Surrogate keys · Conformed, role-playing, junk, degenerate dimensions.

Transaction · Periodic snapshot · Accumulating snapshot · Factless. Measures: additive, semi-additive, non-additive.

0 keep · 1 overwrite · 2 new row + ValidFrom/ValidTo/IsCurrent · 3 previous-value column · 4 history table · 6 hybrid.

Staging · audit table · error tables · Unknown member (-1) · idempotent reruns · watermark updated after success · reconciliation counts/sums · alerts.

Inmon (top-down 3NF) · Kimball (bottom-up stars) · Data Vault (hubs/links/satellites) · Data lake · Lakehouse · Medallion bronze → silver → gold.

SSIS · ADF · Fabric · Synapse · Databricks · Informatica · Talend · Airflow · dbt · Spark · Kafka.

Package (.dtsx) · Project (.ispac) · Control Flow (tasks, containers, precedence constraints) · Data Flow (sources, transformations, destinations) · Connection managers · Variables · Parameters · Event handlers · Log/SSISDB.

Execute SQL · Data Flow · Execute Package · File System · FTP · Script · Send Mail · Expression · Bulk Insert · CDC Control.

• Non-blocking: Derived Column, Data Conversion, Conditional Split, Lookup, Multicast, Row Count, Copy Column, Audit.
• Semi-blocking: Merge, Merge Join, Union All, Pivot/Unpivot.
• Fully blocking: Sort, Aggregate, Fuzzy Lookup/Grouping.

Full (default, fastest) · Partial · No cache · Cache Connection Manager. Case/space/type sensitive.

Error output: Fail / Ignore / Redirect row · OnError event handler · MaximumErrorCount · Propagate=False · checkpoints · audit table.

Project model → SSISDB → folder → environments (DEV/QA/PROD) → parameter mapping → SQL Agent job → reports. dtexec /ISServer ... /Env n /Par ....

SQL source with filters · no Sort/Aggregate on big data · no OLE DB Command · full-cache lookups · fast load + table lock · buffer tuning · parallel tasks · staging + MERGE · incremental.

Report Designer/Report Builder → RDL → Report Server (service) + ReportServer & ReportServerTempDB → web portal (/Reports) & web service (/ReportServer) → renderers → delivery.

Tablix = Table (dynamic rows) · Matrix (dynamic rows + columns) · List (free-form) · Chart · Gauge · Map · Sparkline · Data bar · Indicator.

Single/multi-value · cascading (child dataset uses parent) · default =Today() · hidden/internal · SP multi-value via Join + STRING_SPLIT.

Drill-down (toggle visibility) · Drill-through (Action → Go to report) · Subreport · Interactive sort · Document map · Bookmarks · Go to URL.

Standard vs data-driven subscriptions (Enterprise) · SQL Agent required · caching · snapshots · shared dataset cache · ExecutionLog3 (DataRetrieval / Processing / Rendering).

Folder/item roles: Browser, Content Manager, Publisher, Report Builder, My Reports · System Administrator/User · back up the encryption key · row-level via User!UserID.

SSRS 2022 = last SSRS · Power BI Report Server for on-prem going forward · paginated reports in Power BI Service.

HTTP.sys (kernel, queue, cache, TLS) → WAS/W3SVC → w3wp.exe (app pool) → integrated pipeline modules → handler (static / ASP.NET / AspNetCoreModuleV2) → logging → response.

CLR v4.0 (Framework) / No Managed Code (Core) · Integrated pipeline · ApplicationPoolIdentity · AlwaysRunning + idle 0 for warm apps · recycle off-peak · rapid-fail → 503.

Hosting Bundle · dotnet publish · web.config aspNetCore (inprocess) · stdout log for 500.30 · app_offline.htm for deploys · one in-process app per pool.

applicationHost.config (server) · web.config (site/app) · bindings + SNI certificates · Windows auth for intranet · URL Rewrite (HTTPS, SPA fallback) · ARR reverse proxy/farms · compression · FREB tracing.

401 auth · 403.14 no default doc · 404.3 MIME · 500.19 config · 500.21 handler · 500.30/502.5 Core startup · 502.3 backend timeout · 503 pool stopped.

Merge = true history, safe for shared branches. Rebase = linear history, rewrites ids — only on your own branches. Squash merge = one commit per PR on main.

GitFlow (develop/release/hotfix, versioned releases) · GitHub Flow (main + short branches) · Trunk-based (daily merges + feature flags).

Never commit secrets (rotate if you do) · --force-with-lease, never --force on shared branches · protect main with PR + CI policies · small PRs, frequent syncs · tag every release.

FROM · WORKDIR · COPY (prefer) / ADD · RUN · ENV / ARG · EXPOSE · USER · HEALTHCHECK · ENTRYPOINT (exec form) + CMD (default args) · multi-stage COPY --from=build.

Images: sdk / aspnet / runtime / runtime-deps · .NET 8+: port 8080, non-root app user · dotnet publish -t:PublishContainer · chiseled images.

Created → Running → Paused → Exited → Removed · stop = SIGTERM then SIGKILL (10 s) · restart policies: no / on-failure / always / unless-stopped.

0 ok · 1 app error · 137 SIGKILL/OOM · 139 segfault · 143 SIGTERM.

Multi-stage · small pinned base · non-root · no secrets in layers · .dockerignore · cache-friendly order · scan images · logs to stdout · health checks · immutable tags.

Control plane: API server · etcd · scheduler · controller manager · cloud controller. Nodes: kubelet · kube-proxy · container runtime.

Pod · ReplicaSet · Deployment · StatefulSet · DaemonSet · Job · CronJob · Service (ClusterIP/NodePort/LoadBalancer/ExternalName/headless) · Ingress / Gateway API · ConfigMap · Secret · PV / PVC / StorageClass · Namespace · ServiceAccount · Role/RoleBinding · NetworkPolicy · HPA · PDB · ResourceQuota.

Liveness → restart · Readiness → remove from endpoints · Startup → delay others.

Requests (scheduling) · Limits (CPU throttle, memory OOMKill) · QoS: Guaranteed / Burstable / BestEffort.

Pending · Running · Succeeded · Failed · Unknown — ImagePullBackOff · CrashLoopBackOff · OOMKilled · CreateContainerConfigError.

Rolling (default) · Recreate · Blue-green · Canary · A/B. Rollback: kubectl rollout undo / helm rollback.

az aks create/get-credentials/upgrade/nodepool add · attach ACR · Workload Identity + Key Vault CSI · Azure CNI · Container Insights · KEDA · AKS Automatic · consider Azure Container Apps for simpler needs.

Boards · Repos · Pipelines · Test Plans · Artifacts.

trigger/pr/schedules → variables/parameters/resources → stages → jobs (job / deployment) → steps (task / script / template).

UseDotNet@2 · DotNetCoreCLI@2 · PublishTestResults@2 · PublishPipelineArtifact@1 · Docker@2 · AzureWebApp@1 · AzureCLI@2 · AzureKeyVault@2 · KubernetesManifest@1 · HelmDeploy@1 · SqlAzureDacpacDeployment@1 · Cache@2 · NuGetAuthenticate@1.

${{ }} compile-time · $[ ] runtime · $( ) macro. Conditions: succeeded(), failed(), always(), eq(), and(), or(), contains().

CI (trigger) · PR (pr) · schedules (cron) · pipeline resources (on another pipeline completing) · manual.

Workload identity federation service connections · Key Vault variable groups · secret masking · branch policies · environment approvals & checks · required templates · least-privilege pipeline permissions.

Trunk-based / GitHub flow / GitFlow · rolling / blue-green (slots) / canary · build once, deploy many · IaC (Bicep/Terraform) · DORA metrics.

Storage redundancy: LRS · ZRS · GRS · RA-GRS · GZRS. Blob tiers: Hot · Cool (30d) · Cold (90d) · Archive (180d). Cosmos consistency: Strong · Bounded Staleness · Session (default) · Consistent Prefix · Eventual. Functions in-process model support ends 10 Nov 2026.

Reliability · Security · Cost Optimization · Operational Excellence · Performance Efficiency.

Managed identity + DefaultAzureCredential · Key Vault · private endpoints · autoscale · deployment slots · IaC · Application Insights · tags + budgets · zones/multi-region for HA.

New app → Azure SQL Database · lift-and-shift with Agent/cross-DB → Managed Instance · full control/SSRS on box → SQL VM · global NoSQL → Cosmos DB · Postgres/MySQL → Flexible Server · cache → Redis.

DTU (Basic/Standard/Premium) or vCore (General Purpose, Business Critical, Hyperscale) · serverless (auto-scale, auto-pause) · elastic pools (many DBs) · Hybrid Benefit + reservations.

Private endpoint · Entra-only auth + managed identity (Authentication=Active Directory Default) · TDE · Always Encrypted · RLS · auditing · Defender for SQL.

Built-in HA (99.99 %) · zone redundancy · geo-replication · failover groups (listener endpoints) · PITR 1–35 days · LTR up to 10 years · geo-restore · retry transient faults.

Partition key (high cardinality, in queries) · RU/s (autoscale/serverless) · consistency: Strong → Bounded → Session (default) → Prefix → Eventual · change feed · point reads cheapest.

IAM (roles!) · EC2 · Elastic Beanstalk · ECS/Fargate · EKS · Lambda · S3 · EBS/EFS · RDS (SQL Server) · Aurora · DynamoDB · ElastiCache · VPC · ALB/NLB · Route 53 · CloudFront · API Gateway · SQS/SNS/EventBridge · CloudWatch · CloudTrail · KMS/Secrets Manager · Cognito.

App Service ↔ Beanstalk/App Runner · Container Apps ↔ Fargate · AKS ↔ EKS · Functions ↔ Lambda · Blob ↔ S3 · Azure SQL ↔ RDS · Cosmos DB ↔ DynamoDB · Service Bus ↔ SQS/SNS · Key Vault ↔ Secrets Manager · Monitor ↔ CloudWatch · Bicep ↔ CloudFormation/CDK.

2+ AZs · ALB + auto scaling · Multi-AZ RDS · stateless apps · queues for spikes · Route 53 failover for DR.

Root MFA, no keys · least-privilege policies · roles for apps · private subnets for data · security groups chain · KMS encryption · Secrets Manager · CloudTrail on · WAF on public endpoints.

Right-size · Savings Plans/RIs · Spot for batch · Graviton · serverless for spiky · S3 lifecycle · VPC endpoints · Budgets + tags.

Compute Engine · Cloud Run · GKE (Autopilot) · Cloud Run functions · Cloud Storage · Cloud SQL (SQL Server/Postgres/MySQL) · AlloyDB · Spanner · Firestore · Bigtable · Memorystore · BigQuery · Pub/Sub · Eventarc · Cloud Tasks · Load Balancing · Cloud CDN · Cloud Armor · Secret Manager · Cloud KMS · Logging/Monitoring/Trace · Cloud Build · Artifact Registry · Vertex AI.

Org → folders → projects → resources · predefined roles · service accounts for workloads · Workload Identity Federation (no keys) · org policies.

Container on Cloud Run (listen on PORT) · Cloud SQL via private IP or Auth Proxy · secrets via --set-secrets · JSON logs to stdout · Cloud Build/GitHub Actions deploy.

Sustained & committed use discounts · Spot VMs · scale to zero · budgets · BigQuery partition/cluster · lifecycle rules.

Global VPC · global load balancer with one anycast IP · strongest analytics (BigQuery) · Kubernetes origin (GKE) · per-second billing.

header > nav · main > article > section · aside · footer · one h1, headings in order · button for actions, a for navigation · labels for every input.

inline > id (1,0,0) > class/attr/pseudo-class (0,1,0) > element (0,0,1); equal → last wins; !important overrides; @layer order before specificity.

Viewport meta · mobile-first min-width queries · no fixed widths · max-width:100% images · min-width:0 on grid/flex children · overflow wrappers for tables/code · container queries for components · test 320 → 1920 px.

Alt text · labels · keyboard + visible focus · contrast 4.5:1 · lang · landmarks · ARIA only when needed · prefers-reduced-motion.

Primitives: string, number, bigint, boolean, undefined, null, symbol. Falsy: false, 0, -0, 0n, "", null, undefined, NaN. Use ===. Array.isArray, Number.isNaN, typeof null === "object".

const by default · let when reassigning · no var · TDZ for let/const · function declarations fully hoisted.

method → object · plain → undefined (strict) · new → instance · call/apply/bind → explicit · arrow → lexical.

Sync code → all microtasks (promises, queueMicrotask) → render → next macrotask (setTimeout, events, I/O).

all (fail fast) · allSettled (all outcomes) · race (first settled) · any (first success) · async/await + try/catch · AbortController.

map · filter · reduce · find · findIndex · some · every · includes · flat · flatMap · at · toSorted · Object.groupBy · sort((a,b)=>a-b) (default sort is lexicographic!).

?. · ?? · ??= · destructuring · spread/rest · template literals · classes with #private · modules · top-level await · structuredClone.

querySelector(All) · textContent (safe) vs innerHTML (XSS risk) · addEventListener · delegation with closest · bubbling vs capturing · preventDefault / stopPropagation.

string number boolean bigint symbol · T[] / Array<T> · tuple [A, B] · unknown (safe) vs any (unsafe) · never · void · literal types "a" | "b" · as const.

Interface: object contracts, extends, declaration merging. Type: unions, tuples, mapped/conditional types, & intersections.

typeof · instanceof · in · discriminant switch + never default · x is T guards · asserts x is T.

Partial Required Readonly Pick Omit Record Exclude Extract NonNullable ReturnType Parameters Awaited.

strict: true · avoid any and as · unknown for external data · validate API responses (Zod) · generate types from OpenAPI · import type for type-only imports · tsc --noEmit in CI.

V8 (JS engine) + libuv (event loop, thread pool of 4, async I/O) · your JS on one main thread · I/O non-blocking · CPU work → worker threads.

sync code → process.nextTick → promise microtasks → timers → pending → poll (I/O) → check (setImmediate) → close callbacks.

express.json() · routers per feature · middleware order matters · (err, req, res, next) error handler · Express 5 async errors · helmet, cors, rate limit, validation.

mssql ConnectionPool once · .input(name, type, value) parameters · .execute(proc) · sql.Transaction · encrypt: true (Azure) · Prisma provider = "sqlserver" · secrets in env vars.

LTS (even) versions · npm ci · NODE_ENV=production · PM2/cluster or containers · graceful SIGTERM shutdown · pino logging · monitor event-loop lag and heap.

$(fn) DOM ready · $("css") select · $(el) wrap · $("<li>", {text}) create · chaining · implicit iteration · $.noConflict().

find · filter · not · eq · first/last · parent/parents/closest · children/siblings/next/prev · is · has.

text · html · val · attr · prop · data · addClass/removeClass/toggleClass · css · append/prepend/after/before · appendTo · remove/detach/empty · clone.

on(event, [selector], handler) · off · one · trigger · namespaces click.ns · e.preventDefault() · return false = prevent + stop.

$.ajax({url, method, data, contentType, dataType}) · $.get · $.post · $.getJSON · .load() · .done/.fail/.always/.then · $.when · ajaxStart/ajaxStop.

show/hide/toggle · fadeIn/fadeOut/fadeToggle · slideUp/slideDown/slideToggle · animate · stop · delay.

1.7 .on() · 1.9 removed .live() · 3.0 Promises/A+ · 3.5 XSS fix · 4.0 (2026) drops old IE, ES modules.

querySelector · classList · textContent · dataset · addEventListener + closest · fetch · CSS transitions.

module · controller (controller-as vm) · $scope / $rootScope · directives · components (1.5+) · filters · services · DI · routing · digest cycle.

ng-app · ng-controller · ng-model · ng-bind · ng-repeat (track by) · ng-if · ng-show/hide · ng-switch · ng-class · ng-click · ng-submit · ng-options · ng-include · ng-cloak · ng-messages.

constant (config-safe) · value · factory (returns object) · service (new) · provider ($get, configurable).

@ string · < one-way · = two-way · & callback. Component hooks: $onInit, $onChanges, $doCheck, $postLink, $onDestroy.

watchers + dirty checking · $apply (outside AngularJS) · $applyAsync · $watch / $watchCollection / deep watch · max 10 iterations · $emit up / $broadcast down / $on.

1.0 2012 · 1.5 components · 1.6 removed .success/.error · 1.8.3 last · EOL 31 Dec 2021 · migrate with ngUpgrade.

:: one-time binding · track by · fewer watchers · debounce ng-model · no heavy template filters · debugInfoEnabled(false).

ng new · ng serve · ng g c|s|p|d|g · ng build · ng test · ng add · ng update.

{{ }} · [prop] · (event) · [(ngModel)] · [class.x] · [style.x] · [attr.x].

@if / @else · @for (x of xs; track x.id) {} @empty {} · @switch / @case · @defer (on viewport) · @let.

signal() · computed() · effect() · linkedSignal() · resource() · input() · output() · model() · viewChild() · toSignal() / toObservable().

constructor → ngOnChanges → ngOnInit → ngDoCheck → ngAfterContentInit/Checked → ngAfterViewInit/Checked → ngOnDestroy.

switchMap (cancel) · mergeMap (parallel) · concatMap (sequential) · exhaustMap (ignore while busy) · debounceTime · distinctUntilChanged · catchError · retry · forkJoin · combineLatest · shareReplay · takeUntilDestroyed · BehaviorSubject.

provideRouter(routes) · loadComponent / loadChildren · guards CanActivateFn / CanMatchFn / CanDeactivateFn · ResolveFn · routerLink · <router-outlet />.

Template-driven (ngModel) vs Reactive (FormGroup, FormControl, FormArray, Validators, typed) · Signal Forms (v21, experimental).

OnPush · signals · zoneless · lazy routes · @defer · track · virtual scroll · SSR + hydration · NgOptimizedImage · no functions in templates.

2 (2016) · 9 Ivy · 14 standalone · 16 signals · 17 control flow + @defer · 19 standalone default · 20 stable signals · 21 zoneless default + Vitest · major every 6 months, 18-month support.

Components = functions returning JSX · props down, callbacks up · state triggers re-render · keys for lists · immutable updates · fragments <>...</>.

useState · useEffect (deps, cleanup) · useLayoutEffect · useRef · useMemo · useCallback · useContext · useReducer · useId · useTransition · useDeferredValue · useSyncExternalStore · React 19: use · useActionState · useFormStatus · useOptimistic · 19.2: useEffectEvent.

none = every render · [] = mount/unmount · [x] = when x changes · cleanup before re-run and on unmount · abort fetches.

Top level only · React functions only · names start with use.

Profile → colocate state → memo + stable props (or React Compiler) → virtualise lists → lazy + Suspense → transitions → TanStack Query caching → SSR/RSC.

Local useState · complex useReducer · subtree Context · server data TanStack Query · global Zustand/Redux Toolkit · URL params · forms React Hook Form.

CSR · SSR + hydration · SSG/ISR · Server Components ("use server" actions, "use client" components) · Next.js App Router.

16.8 Hooks (2019) · 18 concurrent + batching (2022) · 19 Actions + RSC stable (Dec 2024) · 19.2 Activity (Oct 2025) · React Compiler 1.0 · CRA deprecated (2025).

app/ routes · page.tsx · layout.tsx · loading.tsx · error.tsx · not-found.tsx · route.ts (API) · [id] dynamic · [...slug] catch-all · (group) · _private · proxy.ts (middleware) · public/ static.

Server by default (async, DB, secrets, zero JS) · "use client" for state/events · keep client components small · import "server-only" for DB code.

Static + generateStaticParams · ISR revalidate · on-demand revalidatePath/Tag · dynamic per request · streaming Suspense · Cache Components "use cache" (16).

mssql pool on globalThis · Node runtime · env vars (no NEXT_PUBLIC_) · parameterised queries · or Prisma sqlserver · or call an ASP.NET Core API.

Vercel (git push) · output: "standalone" for Docker/Azure/IIS (reverse proxy) · output: "export" for static sites.

{{ }} · :prop · @event.prevent · v-model.trim/.number/.lazy · v-if/v-else-if/v-else · v-show · v-for="(x, i) in xs" :key="x.id" · #slot · <component :is>.

ref (.value) · reactive · computed · watch (lazy, specific) · watchEffect (immediate, auto-track) · toRefs / storeToRefs · shallowRef · readonly · nextTick.

defineProps · defineEmits · defineModel (3.4) · defineExpose · defineOptions · defineSlots · withDefaults.

setup → onBeforeMount → onMounted → onBeforeUpdate → onUpdated → onBeforeUnmount → onUnmounted (+ onErrorCaptured, onActivated/onDeactivated).

props ↓ · emits ↑ · v-model ↕ · provide/inject (deep) · Pinia (global) · template ref + defineExpose.

<Transition> · <TransitionGroup> · <KeepAlive> · <Teleport> · <Suspense> · defineAsyncComponent.

Vite · Vue Router 4 (guards: beforeEach, beforeEnter, onBeforeRouteLeave) · Pinia · VueUse · Vitest + Vue Test Utils · Nuxt 4.

2.0 (2016) · 2.7 (2022) · Vue 2 EOL 31 Dec 2023 · 3.0 (2020) · 3.2 script setup · 3.4 defineModel · 3.5 props destructure, useTemplateRef · 3.6 Vapor Mode (in development).

Many unit → some API/integration → few UI. Automate regression, smoke, data-driven, API contracts; keep exploratory and usability manual.

POM/components · driver factory · config per env · explicit waits only · data via API · independent tests · parallel-safe · screenshots/traces on failure · reports · CI categories (smoke/regression).

Condition waits · stable locators · own data per test · mock unstable dependencies · quarantine + fix · retries only as a visible, temporary measure.

0 field devices · 1 PLC/DCS control · 2 SCADA/HMI · 3 MES/historian · 4 ERP. DMZ between 3 and 4.

Scan: inputs → program → outputs → housekeeping. Languages: LD, FBD, ST, SFC (IL deprecated). Timers TON/TOF/TP; counters CTU/CTD; edges R_TRIG/F_TRIG.

Digital 24 V (PNP/NPN) · 4–20 mA (live zero, broken-wire detection) · 0–10 V · scaling (raw−rMin)/(rMax−rMin)×(eMax−eMin)+eMin.

Coils FC01/05/15 · discrete inputs FC02 · input registers FC04 · holding registers FC03/06/16 · TCP port 502 · two registers per float — check word order · no security.

Nodes + information model · read/write/subscribe/methods/history/alarms · certificates + encryption · opc.tcp://host:4840 · PubSub over MQTT · companion specs.

E-stop NC and on safety PLC/hard-wired · SIL/PL · IEC 62443 zones & conduits · no internet to PLCs · audited writes only.

Industry 4.0 = CPS + IIoT + cloud/edge + analytics/AI · IT/OT convergence · vertical (sensor→ERP) and horizontal (supply chain) integration · Industry 5.0 = human-centric, resilient, sustainable.

ISA-95: 0 field · 1 PLC · 2 SCADA/HMI · 3 MES/historian · 4 ERP. ERP plans (days), MES executes (minutes), PLC controls (ms).

OEE = Availability × Performance × Quality · A = run/planned · P = ideal cycle × count / run · Q = good/total · six big losses · world class ≈ 85 %.

OPC UA (machine access, information model, security) · MQTT (pub/sub, QoS 0/1/2, retained, LWT) · Sparkplug B (namespace + birth/death) · Unified Namespace on an MQTT broker.

Real-time OEE & downtime · traceability/genealogy · SPC & quality · predictive maintenance · energy monitoring · digital twin & virtual commissioning · computer-vision inspection · AI assistants.

Worker Service edge (OPC UA .NET, NModbus, MQTTnet) · IoT Hub/Event Hubs · ASP.NET Core API + SignalR · SQL Server (RLS, columnstore, partitions) + time-series DB · Angular/React dashboards · Docker/K8s · OpenTelemetry.

Block · hash · Merkle root · node · consensus · mempool · confirmation · finality · fork · wallet · private/public key · address · seed phrase · gas · nonce · smart contract · EVM · ABI · token · dApp · oracle · bridge · L1/L2.

PoW (Bitcoin, mining) · PoS (Ethereum since Sep 2022, staking, slashing, 32 ETH validator, 12 s slots, ~12.8 min finality) · DPoS · BFT · PoA.

BTC: 2009, PoW, 10-min blocks, 21M cap, UTXO, halving every ~4 years. ETH: 2015, PoS, 12-s blocks, account model, smart contracts, 1 ETH = 10^18 wei, EIP-1559 fee burn.

ERC-20 fungible · ERC-721 NFT · ERC-1155 multi-token · ERC-4626 vaults · ERC-2612 permit · ERC-4337 account abstraction · EIP-712 typed signing · ERC-4361 Sign-In with Ethereum.

Optimistic rollups (Arbitrum, Optimism, Base — 7-day challenge) · ZK rollups (zkSync, Starknet, Scroll, Linea) · sidechains (Polygon PoS) · Lightning (BTC) · EIP-4844 blobs (2024).

The DAO hack 2016 · EIP-1559 2021 · The Merge 2022 · Shanghai 2023 · Dencun 2024 · Pectra May 2025 · Fusaka Dec 2025.

Solidity · Hardhat / Foundry / Remix · OpenZeppelin · ethers.js v6 / viem / wagmi · Nethereum (.NET) · MetaMask · Infura/Alchemy · Etherscan · Sepolia testnet · IPFS · The Graph · Chainlink.

Seed phrase = ownership · limit approvals · audits · reentrancy · oracle manipulation · flash loans · bridge risk · MEV · multisig + timelock admins.

public · external · internal · private (still readable on-chain) · view · pure · payable.

storage (persistent, costly) · memory (temporary) · calldata (read-only inputs, cheapest) · stack · transient (per-tx, 0.8.28).

require · revert CustomError() · assert (Panic) · try/catch for external calls · all state rolled back.

CEI + nonReentrant · msg.sender not tx.origin · access control on every admin function · SafeERC20 · no spot-price oracles · no unbounded loops · pull payments · nonces + chainid in signatures · Chainlink VRF for randomness · initializers + _disableInitializers for proxies · multisig + timelock · audits + fuzzing.

Fewer SSTOREs · cache reads · pack slots · constant/immutable · calldata · custom errors · unchecked loops · events over storage · optimizer.

Remix · Foundry (forge/cast/anvil) · Hardhat · OpenZeppelin · Slither · Echidna · Tenderly · Etherscan verify · Sepolia.

0.5 explicit locations · 0.6 virtual/override, receive/fallback · 0.8 checked math · 0.8.4 custom errors · 0.8.28 transient storage · OpenZeppelin 5.x.

UI service → interceptor (JWT) → CORS preflight → Kestrel → exception handler → routing → CORS → authN → authZ → endpoint → validation → service → EF Core / Dapper → SQL Server → DTO → JSON → UI state → render.

• Server-side paging, projection to DTOs, AsNoTracking for reads
• Index for every important WHERE + ORDER BY; read the execution plan
• No N+1, no query inside a loop, no .Result/.Wait()
• Cache reference data (IMemoryCache/HybridCache/Redis)
• UI: lazy routes, debounce + cancel, virtual scrolling, OnPush/signals or memo

• HTTPS + HSTS; JWT from a trusted IdP; policies, not only roles
• Ownership checks on every resource (no IDOR)
• Parameterised SQL only; validate all input
• CORS limited to known origins; rate limiting
• Secrets in Key Vault with Managed Identity; nothing sensitive in logs or JWT payload

Business → Frontend → API layers → Data → Security → CI/CD & hosting → My contribution + one number.

Idempotency key · outbox pattern · correlation id · ProblemDetails · optimistic concurrency (ROWVERSION) · covering index · keyset paging · modular monolith · Managed Identity · deployment slots · feature flags · health checks.

• STAR: Situation · Task · Action (60%, "I") · Result (numbers + learning).
• Tell me about yourself: Present → Past → Future → why this role (60–90 s).
• Why us: Company → Role → You.
• Weakness: real + not fatal + what you're doing about it + proof of progress.

Biggest achievement · conflict · failure/mistake · tight deadline · disagreement with manager · leadership/mentoring · learning something fast · customer/stakeholder issue · going beyond your role · process improvement.

Badmouth employers · lie (background checks verify) · say "no questions" · give a salary number before researching · ramble beyond 2 minutes · use only "we".

Research the company · tailor examples to the JD · quantify results · ask 2–3 questions · send a thank-you email · keep your story consistent with your resume and LinkedIn.

Camera at eye level · light in front · headphones · notifications off · resume + JD + pitch notes open · join 5 minutes early · water nearby.

90-day success · team challenges · team structure · engineering practices · growth/reviews · next steps.

Context → my approach (principles) → concrete example (STAR) → result/metric → what I learned.

Roles: PO · Scrum Master · Developers. Events: Sprint · Planning · Daily (15 min) · Review · Retro. Artifacts: Product Backlog (Product Goal) · Sprint Backlog (Sprint Goal) · Increment (DoD). Scrum Guide 2020.

INVEST stories · acceptance criteria · story points + planning poker · velocity · three-point/PERT (O + 4M + P)/6 · MoSCoW · risk register · RAG status.

1:1s · SBI feedback · situational leadership (direct → coach → support → delegate) · Tuckman (form, storm, norm, perform) · psychological safety · PIP as last resort.

Definition of Done · WIP limits · change requests · ADRs · blameless post-mortems (5 Whys) · DORA metrics · tech-debt budget 15–20%.

"Here are three options and my recommendation." · "What will we drop to add this?" · "Disagree and commit." · "Let's restore service first, then find root cause." · "What does success look like for you?"

Blaming the team · hero culture · comparing individuals by velocity · hiding bad news · promising dates without the team's estimate.

Reason (1 line) → what I did (projects, certifications, freelancing, caregiving) → proof (GitHub, certificate) → ready and committed now. Never lie; keep it under 30 seconds.

Profile (role, YOE, skills, city, company type) → 3+ data sources → range (low/median/high) → walk-away, target, anchor numbers.

CTC · fixed · variable · basic · HRA · special allowance · employer PF (12% of basic) · gratuity (after 5 years) · joining bonus (clawback) · ESOP/RSU vesting · in-hand = gross − PF − professional tax − TDS · old vs new tax regime.

Monthly salary × 12 + year-end bonus (not guaranteed) · labour + health insurance · employer pension ≥ 6% · probation · work permit / Gold Card · minimum wage 2026 NT$29,500/month (verify).

Thank → ask time → compare with data → one clear justified ask → negotiate the package (bonus, buyout, review, level, remote) → get it in writing → decide.

"Based on market data for this role…" · "I'm flexible on the structure of the package…" · "Is there flexibility on the fixed component?" · "Could a joining bonus or an earlier review bridge the gap?"

Written offer first · tell manager personally · short positive email · handover plan · relieving/experience letters · final settlement · PF transfer (UAN) · return assets · no burned bridges.

TCS NQT (Ninja/Digital/Prime) · Infosys (Systems Engineer / Specialist Programmer / Digital Specialist Engineer, HackWithInfy) · Wipro Elite NLTH · Cognizant GenC tiers · Accenture cognitive + technical + coding + communication · Capgemini game-based + pseudo-code.

Customer Obsession · Ownership · Invent and Simplify · Are Right, A Lot · Learn and Be Curious · Hire and Develop the Best · Insist on the Highest Standards · Think Big · Bias for Action · Frugality · Earn Trust · Dive Deep · Have Backbone; Disagree and Commit · Deliver Results · Strive to be Earth's Best Employer · Success and Scale Bring Broad Responsibility.

Official careers pages · Glassdoor · AmbitionBox · LeetCode Discuss · GeeksforGeeks experiences · Blind · Reddit · PTT Tech_Job (Taiwan) · recruiter.

60–90 s introduction · project deep-dive with a diagram · 8–10 STAR stories · core fundamentals · coding patterns · 2–3 smart questions · researched salary range.