Search the practice set
275 questions, 991 terms and 600 topics in 30 areas.
60 results for “Web Performance Budgets”
Performance Budget Enforcement
A stated limit on bundle size or a timing metric that fails a build when exceeded, which is what turns performance from a periodic project into a constraint.
Performance Budget
A stated numeric limit on a performance characteristic, enforced automatically so that regressions fail a build rather than accumulating.
Application Performance Monitoring
Instrumentation inside the application that attributes latency and errors to specific code paths, queries and dependencies.
JSON Web Token
A signed, self-contained token carrying claims, which a service can validate locally without calling the issuer.
Web Application Firewall
A filter in front of an application that inspects HTTP requests and blocks those matching known attack patterns — useful as a layer, dangerous as a substitute.
APM Transaction Tracing
Instrumentation that attributes application latency and errors to specific code paths, database queries and external calls, usually with automatic tracing.
Arrival Rate Model
Driving a load test by requests arriving per second regardless of how the system responds, rather than by a fixed number of virtual users.
Bandwidth-Delay Product
Bandwidth multiplied by round-trip time — the amount of data that must be in flight to keep a link fully utilised.
Binary Serialisation
Encoding messages compactly using a schema rather than as self-describing text, trading readability for size and parse speed.
Bloom Filter
A compact probabilistic structure that answers "is this key definitely absent, or possibly present?" — no false negatives, tunable false positives.
Bloom Filter Cache Guard
Placing a Bloom filter in front of an expensive lookup so that keys which certainly do not exist never reach it.
Burstable Instance
An instance that provides a low baseline CPU allocation and accrues credits while idle, spendable for short periods of full performance.
Cache Hit Ratio Economics
The non-linear relationship between cache hit rate and backend load, which determines whether a cache improvement is worth making.
Cache Invalidation
The problem of removing or refreshing cached data when the underlying source changes, and the reason caching is harder than it looks.
Caching Strategy
The chosen pattern for how a cache is populated, read and invalidated — cache-aside, read-through, write-through or write-behind.
Cardinality Estimation
The planner's prediction of how many rows each step of a query will produce — the input that determines every other choice it makes.
Compute Isolation Boundary
The line across which one domain's analytical workload cannot affect another's performance, cost attribution or access.
Concurrency
The number of operations in progress at once — distinct from parallelism, which is how many are literally executing simultaneously.
Connection Pool
A fixed set of reusable database connections shared by an application's requests, and one of the most common hidden capacity ceilings.
Cost Per Transaction
Infrastructure cost divided by business volume, which reveals efficiency trends that absolute spend conceals.
Covering Index
An index that contains every column a query needs, so the query is answered from the index without reading the table at all.
Cumulative Layout Shift
The extent to which visible content moves unexpectedly during load, which correlates with mis-taps and is almost entirely preventable by reserving space.
DORA Metrics
Four measures of software delivery performance — deployment frequency, lead time for change, change failure rate, and time to restore service.
Database Index
A secondary structure that lets the engine find rows without scanning, trading write cost and storage for read speed.
Denormalisation
Deliberately duplicating data across records to make reads cheap, accepting the write-time cost of keeping copies in step.
Error Budget Policy
The written agreement about what happens when the error budget is exhausted, which is what turns an SLO from a number into a control.
Google Maps and Planetary-Scale Spatial Serving
Map serving is fast because almost nothing is computed on request — the world is precomputed into a pyramid of tiles, and space is indexed onto a one-dimensional curve.
HTTP/2 Multiplexing
Carrying many concurrent request/response streams over a single TCP connection, removing the need for multiple connections per origin.
Hedged Request
Sending a duplicate of a request to a second replica after a short delay and using whichever response returns first, to cut tail latency.
Horizontal vs Vertical Scaling
Adding more machines versus making one machine bigger — and the fact that vertical is underrated for stateful tiers.
Mobile conversion is 40% below desktop. Product blames the design; analytics shows users leaving before the page is usable. How do you investigate?
Get field data before touching anything A laboratory run on a developer machine measures one configuration, usually the fastest one anyone uses. Real traffic in
You are designing APIs for a platform with a web app, a mobile app, internal service-to-service traffic and third-party partners. What do you expose, and where?
What the interviewer is testing Whether you choose per constraint or adopt one technology as an identity. The wrong answers here are all defensible sounding and
A dashboard query that took 200ms now takes 40 seconds. The table has grown to 200 million rows. Walk me through diagnosis and fix, including what you would not do.
What the interviewer is testing Whether you diagnose with evidence before changing anything, and whether you know the costs of the fixes you propose. Diagnosis,
A global SaaS product has a 200 ms p95 API budget. Users in Sydney see 900 ms against a single US-East deployment. The application team says the service responds in 40 ms. Who is right and what do you do?
Both are right, and that is the point The service does respond in 40 ms. The other 860 ms is network — and no amount of application profiling will show it, whic
A marketing site is a client-rendered single-page application. Organic traffic is poor and the team blames the search engine. What is your assessment?
The rendering choice is the problem A marketing page is identical for every visitor and highly cacheable. Rendering it in the browser pays for personalisation t
A product catalogue page does 40,000 reads per second against a database that can serve 5,000. Walk me through the caching design, including what happens at 3 AM when the cache is empty.
What the interviewer is testing Whether you can design a cache including its failure modes, rather than saying "put Redis in front of it". The base design Cache
A service's p99 latency has tripled over three months with no single obvious change. How do you investigate?
Establish the shape before touching anything Is it everything or something? Break the metric down by endpoint, tenant, region, instance and version. A tripling
A table has 14 indexes and writes have become slow. How do you decide which to remove?
The approach 1. Get usage statistics, not opinions. Every major engine reports index scan counts — PostgreSQL's pg stat user indexes , SQL Server's sys.dm db in
A team is about to launch a public GraphQL API. What must be in place before it goes live?
Query cost control — the security requirement An arbitrary query language exposed publicly means a client can construct a query that consumes unbounded resource
An executive asks why the new system "feels slower" when your dashboards show average response time improved. How do you explain it?
The average is the problem, and that is the explanation Averages hide the tail. A system where most requests got faster and the slowest ten percent got much slo
Web Performance Budgets
A number a build can fail against, rather than a performance sprint once a year.
Performance Budgets
Targets enforced in CI so regressions fail the build.
Application Performance Monitoring
Attributing latency to code paths, queries and dependencies.
Caching for Performance
Layer choice, hit ratio as a first-class metric, and cold-cache recovery.
Core Web Vitals
LCP, INP and CLS — what they measure, and the architecture that moves them.
Database Performance
Plans, indexes, contention and the pool in front of the database.
Error Budgets
Unreliability as a resource that feature velocity spends.
Network Performance
Latency floors, bandwidth-delay product, and what no code change fixes.
Network Performance Tuning
Keep-alive, compression, payload size and round-trip elimination.
Performance & Capacity
General material on performance and capacity engineering.
Performance Test Design
Workload models, warm-up, think time, and the distribution the average hides.
Performance vs Cost
Buying latency, and knowing what the last millisecond is worth.
Bottleneck Analysis
Finding the constraint, and expecting a second one behind it.
Capacity Modelling
Arithmetic before load tests, and headroom for failure as well as peak.
Concurrency
Operations in flight, and the limits that are the real capacity ceiling.
Connection Pooling
The most common hidden ceiling, and the metric nobody collects.
Cost Governance
Budgets, anomaly alerts, quotas and preventive policy.
Data Virtualisation
Querying across sources without moving data, and the performance ceiling that imposes.
Horizontal vs Vertical Scaling
Scale out for stateless, scale up first for stateful.