Error map
N+1 queries Performance: N+1 query problem (one query per row in a loop)
SQL · layer 5, Data
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
Cloudflare Error 524: A Timeout Occurred
Cloudflare connected to the origin, but the origin didn’t send an HTTP response within 100 seconds.
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
A lazy-loaded association was accessed after the Hibernate session/transaction closed.
Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. All pooled connections were in use and max pool size was reached.
The application’s connection pool was exhausted — all connections busy or leaked.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
HTTP 304 Not Modified
The cached copy is still valid, so the server sends no body and the client reuses its cache.
Cloudflare Error 1200: Cache connection limit
Too many requests are queued at Cloudflare for the origin — the origin is slow and connections pile up.
HTTP 103 Early Hints
An interim response that sends Link headers early so the browser can preload CSS, fonts or scripts while the server is still buil…
Cloudflare not caching: cf-cache-status DYNAMIC / BYPASS / MISS every time
Cloudflare isn’t caching the response — HTML isn’t cached by default, and cookies or Cache-Control headers from the origin preven…
org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing
An entity references another entity that hasn’t been saved yet, and no cascade is configured.
org.hibernate.exception.ConstraintViolationException: could not execute statement
The database rejected an insert/update because of a constraint (unique, foreign key, not null).
System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown
The process couldn’t allocate memory — large in-memory data, leaks, 32-bit process limits, or container memory limits.
Docker build slow: "Sending build context to Docker daemon 2.5GB" / transferring context takes forever
docker build is uploading your whole project folder — node_modules, .git, data files — before building, because there’s no (or a…
Two steps away (35)
PHP Fatal error: Maximum execution time of 30 seconds exceeded
The script ran longer than `max_execution_time` and PHP stopped it.
Cloudflare Error 522: Connection Timed Out
Cloudflare’s TCP connection to your origin timed out — the origin didn’t answer at all.
java.util.concurrent.TimeoutException
A Future.get(timeout) or async operation didn’t complete in the allowed time.
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class X and no properties discovered
Jackson can’t serialize the class — it has no public getters/fields, or it’s a Hibernate proxy, or Java 8 date types without the…
IncorrectResultSizeDataAccessException: query did not return a unique result: 2
A query expected one row but found several.
SequelizeConnectionRefusedError: connect ECONNREFUSED 127.0.0.1:5432
Sequelize couldn’t connect to the database server.
HikariPool-1 - Connection is not available, request timed out after 30000ms
The connection pool was exhausted — all connections were busy for 30 seconds.
ERROR: canceling statement due to statement timeout
A query ran longer than statement_timeout and PostgreSQL cancelled it.
ERROR: out of shared memory — HINT: You might need to increase max_locks_per_transaction.
A transaction took more locks than the lock table can hold — usually touching many tables/partitions at once.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
HTTP 502 Bad Gateway
A proxy or gateway (Nginx, load balancer, CDN) got an invalid response — or no response — from the upstream server behind it.
HTTP 301 Moved Permanently
The resource has a new permanent URL; clients and search engines should use the address in the Location header from now on.
HTTP 412 Precondition Failed
A conditional request header (If-Match, If-Unmodified-Since) didn’t match the current state of the resource.
HTTP 200 OK (but something is still wrong)
The request succeeded at the HTTP level — yet the page is blank, the data is wrong, or an error is hidden inside the response bod…
HTTP 503 Service Unavailable
The server is temporarily unable to handle the request — overloaded, in maintenance, or has no healthy backends.
Cloudflare-branded 502 Bad Gateway / 504 Gateway Timeout ("cloudflare" footer)
A plain-looking 502/504 page with “cloudflare” at the bottom comes from Cloudflare’s network itself (or an origin response it cou…
Cloudflare Error 1016: Origin DNS error
Cloudflare can’t resolve the origin hostname your DNS record points to (usually a CNAME target).
Warning: Cannot modify header information - headers already sent
You called `header()`, `setcookie()` or `session_start()` after output had already been sent to the browser.
CORS Error: No 'Access-Control-Allow-Origin' header is present
The browser blocked a cross-origin request because the server’s response didn’t include the CORS headers allowing your site’s ori…
HTTP 411 Length Required
The server refuses a request with a body but no Content-Length header.
ANR: Application Not Responding (Input dispatching timed out)
The main thread was blocked for about 5 seconds (input) or a broadcast/service took too long, so Android showed “App isn’t respon…
WordPress: Error establishing a Redis connection (object cache)
The persistent object cache drop-in (object-cache.php) can’t connect to Redis, so the whole site fails.
WooCommerce: Sorry, your session has expired. Return to shop
WooCommerce lost the customer’s cart session — usually because checkout/cart pages are cached or cookies are blocked/stripped.
sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) connection to server … failed
SQLAlchemy’s DB driver raised an operational error — connection failures, lost connections or locked SQLite databases.
sqlalchemy.exc.IntegrityError: (psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint
A database constraint (unique, foreign key, not null) rejected an insert/update made through SQLAlchemy.
MySQL ERROR 1062 (23000): Duplicate entry for key
An INSERT/UPDATE would create a duplicate value in a PRIMARY or UNIQUE key.
PostgreSQL: ERROR: duplicate key value violates unique constraint
An INSERT/UPDATE would create a duplicate in a UNIQUE or PRIMARY KEY column — or the id sequence is behind the existing data.
MySQL ERROR 1022 (23000): Can't write; duplicate key in table
An ALTER/CREATE produced a duplicate key or constraint name — often a foreign key name that already exists in the database.
Kubernetes: OOMKilled (exit code 137)
The container used more memory than its limit, and the kernel killed it.
java.lang.OutOfMemoryError: Java heap space
The JVM ran out of heap memory and garbage collection couldn’t free enough.
Blue Screen: MEMORY_MANAGEMENT (Stop code 0x0000001A)
Windows detected a severe memory-management error — commonly faulty RAM, unstable memory settings or a bad driver.
no space left on device (Docker / Linux)
The disk (or inode table) is full — Docker images, build cache, logs and volumes are common culprits.
npm ERR! code ELIFECYCLE / Command failed with exit code 1
An npm script (build, start, test, postinstall) exited with an error. ELIFECYCLE is only the wrapper — the real error is printed…
gyp ERR! build error / node-gyp rebuild failed
A dependency with native C/C++ code couldn’t compile — missing build tools, Python, or an unsupported Node version.
Map another error
Popular: 4035004000xC000007BTypeErrorCritical error404NullPointerException