Error map
Communications link failure com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
Java · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (9). 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 (9)
PDOException: could not find driver
The PDO driver for your database (pdo_mysql, pdo_pgsql, pdo_sqlite) isn’t installed or enabled.
MySQL ERROR 2003 (HY000): Can't connect to MySQL server on 'host:3306' (111)
The client couldn’t reach MySQL over TCP — server down, wrong host/port, firewall, or MySQL bound to localhost only.
MySQL ERROR 2013 (HY000): Lost connection to MySQL server during query
The connection dropped mid-query — server crash/restart, timeouts, or a proxy cutting long queries.
HikariPool-1 - Connection is not available, request timed out after 30000ms
The connection pool was exhausted — all connections were busy for 30 seconds.
MySQL ERROR 1049 (42000): Unknown database 'x'
The database named in the connection doesn’t exist on that server.
PDOException: SQLSTATE[HY000] [2002] Connection refused
PHP couldn’t reach the database server at the host/port in your DSN.
MySQL ERROR 2002 (HY000): Can't connect to local MySQL server through socket
The client couldn’t reach the MySQL server — it isn’t running, or the client is looking for the socket/port in the wrong place.
MySQL ERROR 1040 (08004): Too many connections
MySQL reached `max_connections` and refuses new clients.
MySQL ERROR 2006 (HY000): MySQL server has gone away
The connection to MySQL was closed — usually by a timeout or a packet larger than `max_allowed_packet`.
Two steps away (25)
PHP Fatal error: Uncaught Error: Call to undefined function
PHP can’t find the function you called — usually a missing extension, missing include, or namespace issue.
Fatal error: Uncaught Error: Call to undefined function imagecreatefromjpeg()
The GD extension (or its JPEG/WebP support) isn’t installed for the PHP version serving the site.
Class "NumberFormatter" not found / The "intl" PHP extension is required
Code uses the intl extension (NumberFormatter, Collator, IntlDateFormatter) but it isn’t installed.
Error: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
MySQL ERROR 1130 (HY000): Host 'x' is not allowed to connect to this MySQL server
No MySQL account exists for the host you’re connecting from.
SQL Server: A network-related or instance-specific error occurred while establishing a connection to SQL Server. (provider: Named Pipes Provider, error: 40 / TCP Provider, error: 26)
The client couldn’t reach the SQL Server instance — wrong server name/instance, TCP disabled, firewall, or SQL Browser not runnin…
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
Cloudflare Error 522: Connection Timed Out
Cloudflare’s TCP connection to your origin timed out — the origin didn’t answer at all.
Lock wait timeout exceeded; try restarting transaction (MySQL 1205)
A query waited too long for a row lock held by another transaction and gave up.
MongooseError: Operation `users.find()` buffering timed out after 10000ms
Mongoose queued a query waiting for a connection that never opened.
Error: P1001: Can't reach database server at `host`:`5432`
Prisma couldn’t connect to the database in DATABASE_URL.
MySQL ERROR 1045 (28000): Access denied for user
MySQL rejected the login — wrong password, wrong user/host combination, or the user doesn’t exist.
WordPress: Error Establishing a Database Connection
WordPress can’t connect to its MySQL/MariaDB database with the credentials in wp-config.php, or the database server is down.
MySQL ERROR 1046 (3D000): No database selected
A query referenced tables without a database selected (no USE and no db in the connection).
Error: connect ECONNREFUSED 127.0.0.1:5432
Nothing is listening at that host:port — the target service is down or you’re connecting to the wrong address.
PostgreSQL: could not connect to server / connection refused — Is the server running on host and accepting TCP/IP connections?
The client reached no PostgreSQL listener at that host/port — the server is down, listening elsewhere, or not accepting remote co…
Job for mysql.service failed because the control process exited with error code
The MySQL/MariaDB service failed to start — the real reason is in the MySQL error log.
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
The docker CLI can’t talk to the Docker engine — it isn’t running, or your user can’t access the socket.
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
MySQL ERROR 1114 (HY000): The table 'x' is full
MySQL couldn’t extend the table — disk full, a size limit, or a MEMORY table hitting max_heap_table_size.
MySQL ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL, or READS SQL DATA in its declaration and binary logging is enabled
Creating a stored function failed because binary logging requires it to declare its data access characteristics.
Deadlock found when trying to get lock; try restarting transaction
Two transactions waited on each other’s locks; the database killed one so the other could continue.
MySQL ERROR 1153 (08S01): Got a packet bigger than 'max_allowed_packet' bytes
A single statement or row exceeded max_allowed_packet — big BLOBs, huge INSERTs or large dump lines.
server closed the connection unexpectedly — This probably means the server terminated abnormally before or while processing the request.
The connection to PostgreSQL dropped — the server restarted/crashed, a proxy/firewall killed an idle connection, or the backend w…
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