New Databases articles from OhSudo: practical fixes for DevOps engineers, SysAdmins and IT folks.https://ohsudo.com/en-ushttps://ohsudo.com/articles/oracle-ora-12514-listener-does-not-know-of-service/https://ohsudo.com/articles/oracle-ora-12514-listener-does-not-know-of-service/Fix Oracle ORA-12514: list the services the listener knows, use the right service name, open the PDB, register the database with the listener, and fix LOCAL_LISTENER.Sun, 15 Nov 2026 00:00:00 GMTDatabasesoraclelistenertnspdbsqlplustroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-deadlock-detected/https://ohsudo.com/articles/postgresql-deadlock-detected/Fix PostgreSQL "ERROR: deadlock detected": read which processes and rows were involved, lock rows in a consistent order, and retry on SQLSTATE 40P01.Fri, 13 Nov 2026 00:00:00 GMTDatabasespostgresqllockstransactionsdeadlocktroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-error-1146-table-doesnt-exist/https://ohsudo.com/articles/mysql-error-1146-table-doesnt-exist/Fix MySQL ERROR 1146 "Table doesn't exist": check the database you are in, the case of the name on Linux, migrations, and tables that exist on disk but not in InnoDB.Thu, 12 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbtablescase-sensitivityinnodbtroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mongodb-authentication-failed/https://ohsudo.com/articles/mongodb-authentication-failed/Fix MongoDB "Authentication failed": set authSource correctly, encode special characters in the URI, check which database holds the user, and handle Docker volumes.Wed, 11 Nov 2026 00:00:00 GMTDatabasesmongodbauthenticationmongoshdockerconnection-stringtroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/oracle-ora-01017-invalid-username-password/https://ohsudo.com/articles/oracle-ora-01017-invalid-username-password/Fix Oracle ORA-01017 "invalid username/password": case-sensitive passwords, the wrong service or PDB, expired and locked accounts, old clients, and getting in as SYSDBA.Wed, 11 Nov 2026 00:00:00 GMTDatabasesoracleauthenticationsqlpluspdbpasswordstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/sql-server-error-4060-cannot-open-database/https://ohsudo.com/articles/sql-server-error-4060-cannot-open-database/Fix SQL Server error 4060 "Cannot open database requested by the login": check the database name and state, map the login to a user, and fix logins after a restore.Wed, 11 Nov 2026 00:00:00 GMTDatabasessql-servermssqlloginsrestorepermissionstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-no-pg-hba-conf-entry-for-host/https://ohsudo.com/articles/postgresql-no-pg-hba-conf-entry-for-host/Fix PostgreSQL "FATAL: no pg_hba.conf entry for host": read the host, user and SSL in the message, add a narrow rule to pg_hba.conf, reload it, and handle Docker and SSL.Tue, 10 Nov 2026 00:00:00 GMTDatabasespostgresqlpg-hbaconnectionsssldockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/redis-oom-command-not-allowed/https://ohsudo.com/articles/redis-oom-command-not-allowed/Fix Redis "OOM command not allowed when used memory > maxmemory": read INFO memory, choose an eviction policy, find big keys, set expiry, and raise maxmemory with care.Mon, 09 Nov 2026 00:00:00 GMTDatabasesredismemorymaxmemoryevictioncachetroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-relation-does-not-exist/https://ohsudo.com/articles/postgresql-relation-does-not-exist/Fix PostgreSQL "ERROR: relation does not exist": check the schema and search_path, quoted names with capitals, which database you are in, and whether migrations have run.Sun, 08 Nov 2026 00:00:00 GMTDatabasespostgresqlsqlschemasearch-pathtroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-error-1130-host-is-not-allowed-to-connect/https://ohsudo.com/articles/mysql-error-1130-host-is-not-allowed-to-connect/Fix MySQL ERROR 1130 "Host is not allowed to connect to this MySQL server": see which accounts exist, create one for the right host and grant it access, without root.Sat, 07 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbaccountsgrantconnectionstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/elasticsearch-flood-stage-watermark-read-only/https://ohsudo.com/articles/elasticsearch-flood-stage-watermark-read-only/Fix Elasticsearch "disk usage exceeded flood-stage watermark, index has read-only-allow-delete block": free disk space, check allocation and remove the block if needed.Fri, 06 Nov 2026 00:00:00 GMTDatabaseselasticsearchopensearchdisk-spacewatermarkilmtroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-deadlock-found-when-trying-to-get-lock/https://ohsudo.com/articles/mysql-deadlock-found-when-trying-to-get-lock/Fix MySQL error 1213 "Deadlock found when trying to get lock": read SHOW ENGINE INNODB STATUS, retry the transaction, lock rows in the same order and add missing indexes.Fri, 06 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbinnodbdeadlocktransactionstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-incorrect-string-value-utf8mb4/https://ohsudo.com/articles/mysql-incorrect-string-value-utf8mb4/Fix MySQL error 1366 "Incorrect string value: \xF0\x9F...": utf8 only holds 3 bytes, so convert the table and connection to utf8mb4, and handle index length limits.Fri, 06 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbutf8mb4charsetemojitroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/oracle-ora-12541-no-listener/https://ohsudo.com/articles/oracle-ora-12541-no-listener/Fix Oracle ORA-12541 "TNS:no listener" (or "Cannot connect. No listener at host"): start it with lsnrctl, check the host and port, listener.ora, firewalls and Docker.Fri, 06 Nov 2026 00:00:00 GMTDatabasesoraclelistenerlsnrctltnsconnectionstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-peer-authentication-failed/https://ohsudo.com/articles/postgresql-peer-authentication-failed/Fix PostgreSQL "Peer authentication failed for user": use sudo -u postgres, connect over TCP with -h localhost, or change pg_hba.conf to scram-sha-256 and reload.Fri, 06 Nov 2026 00:00:00 GMTDatabasespostgresqlpg-hbaauthenticationpsqlubuntutroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/redis-noauth-authentication-required/https://ohsudo.com/articles/redis-noauth-authentication-required/Fix Redis "NOAUTH Authentication required" and WRONGPASS: find the password, send it from redis-cli and your client, set it in a URL, and use ACL users in Redis 6+.Fri, 06 Nov 2026 00:00:00 GMTDatabasesredisauthenticationaclredis-clidockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/sql-server-transaction-log-is-full-9002/https://ohsudo.com/articles/sql-server-transaction-log-is-full-9002/Fix SQL Server error 9002 "The transaction log for database is full": read log_reuse_wait_desc, back up the log or end the old transaction, and size the log properly.Fri, 06 Nov 2026 00:00:00 GMTDatabasessql-servermssqltransaction-logbackupdisk-spacetroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mongodb-connect-econnrefused-27017/https://ohsudo.com/articles/mongodb-connect-econnrefused-27017/Fix MongoDB "connect ECONNREFUSED 127.0.0.1:27017" and ::1:27017: start mongod, read exit code 14, check bindIp, IPv6 localhost in Node.js, and Docker service names.Thu, 05 Nov 2026 00:00:00 GMTDatabasesmongodbnodejsconnectionssystemddockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mongodb-e11000-duplicate-key-error/https://ohsudo.com/articles/mongodb-e11000-duplicate-key-error/Fix MongoDB "E11000 duplicate key error": read the index and value in the message, solve dup key null with a partial index, clean up duplicates, handle upsert races.Thu, 05 Nov 2026 00:00:00 GMTDatabasesmongodbindexesmongooseupsertmongoshtroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-cant-connect-through-socket/https://ohsudo.com/articles/mysql-cant-connect-through-socket/Fix MySQL ERROR 2002 "Can't connect to local MySQL server through socket": is the server running, where is the socket, and why localhost differs from 127.0.0.1.Thu, 05 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbconnectionssystemdsocketstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-error-1064-sql-syntax/https://ohsudo.com/articles/mysql-error-1064-sql-syntax/Fix MySQL ERROR 1064: read the "near" text, then check reserved words like rank and groups, quotes, commas, old GRANT syntax and queries written for another database.Thu, 05 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbsqlsyntaxgranttroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-error-2003-cant-connect-to-mysql-server/https://ohsudo.com/articles/mysql-error-2003-cant-connect-to-mysql-server/Fix MySQL ERROR 2003 "Can't connect to MySQL server": the number in brackets says if it's a stopped server, bind-address, a firewall or the wrong host in Docker.Thu, 05 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbbind-addressfirewalldockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/oracle-ora-00942-table-or-view-does-not-exist/https://ohsudo.com/articles/oracle-ora-00942-table-or-view-does-not-exist/Fix Oracle ORA-00942 "table or view does not exist": the table may exist. Check the schema, your privileges, quoted lowercase names, synonyms and roles inside PL/SQL.Thu, 05 Nov 2026 00:00:00 GMTDatabasesoraclesqlpermissionsschemapl-sqltroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/oracle-ora-12154-tns-could-not-resolve/https://ohsudo.com/articles/oracle-ora-12154-tns-could-not-resolve/Fix Oracle ORA-12154: the client can't find your connect identifier. Check tnsnames.ora, TNS_ADMIN and sqlnet.ora, an @ in the password, or use Easy Connect.Thu, 05 Nov 2026 00:00:00 GMTDatabasesoracletnsnamessqlplusconnectionstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-sorry-too-many-clients-already/https://ohsudo.com/articles/postgresql-sorry-too-many-clients-already/Fix PostgreSQL "FATAL: sorry, too many clients already": see who holds the connections, end the idle ones, size your pools, and add PgBouncer before raising the limit.Thu, 05 Nov 2026 00:00:00 GMTDatabasespostgresqlconnectionspgbouncermax-connectionsperformancetroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/sql-server-login-failed-for-user-18456/https://ohsudo.com/articles/sql-server-login-failed-for-user-18456/Fix SQL Server error 18456 "Login failed for user": find the real reason in the log by its state, then fix the password, mixed mode, a disabled login or the database.Thu, 05 Nov 2026 00:00:00 GMTDatabasessql-servermssqlauthenticationssmssqlcmdtroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/sql-server-network-related-instance-specific-error/https://ohsudo.com/articles/sql-server-network-related-instance-specific-error/Fix SQL Server "A network-related or instance-specific error occurred": check the service, TCP/IP, the instance name, SQL Browser, port 1433 and the Windows firewall.Thu, 05 Nov 2026 00:00:00 GMTDatabasessql-servermssqlwindows-serverfirewallconnectionstroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-error-1040-too-many-connections/https://ohsudo.com/articles/mysql-error-1040-too-many-connections/Fix MySQL and MariaDB "Too many connections": log in with the reserved admin connection, find idle and stuck connections, then fix pools, timeouts or max_connections.Mon, 02 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbconnectionsconnection-poolperformancetroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-column-must-appear-in-group-by/https://ohsudo.com/articles/postgresql-column-must-appear-in-group-by/Fix the GROUP BY error in PostgreSQL: understand why it happens, then aggregate the column, group by it or by the primary key, or pick one row per group with DISTINCT ON.Mon, 02 Nov 2026 00:00:00 GMTDatabasespostgresqlsqlgroup-byaggregatesmysqltroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-connection-refused/https://ohsudo.com/articles/postgresql-connection-refused/Fix PostgreSQL "connection refused": check that it runs, read why it did not start, then fix listen_addresses, the port, the firewall or Docker.Mon, 02 Nov 2026 00:00:00 GMTDatabasespostgresqlconnectionssystemdnetworkingdockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-invalid-input-syntax-for-type-integer/https://ohsudo.com/articles/postgresql-invalid-input-syntax-for-type-integer/Fix "invalid input syntax for type integer": find empty strings and text where a number is expected, convert with NULLIF and pg_input_is_valid, import clean data.Mon, 02 Nov 2026 00:00:00 GMTDatabasespostgresqlsqltypescastingcsvimporttroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-password-authentication-failed/https://ohsudo.com/articles/postgresql-password-authentication-failed/Fix PostgreSQL "password authentication failed" and "Peer authentication failed": read the server log, check pg_hba.conf, reset the password, and handle Docker.Mon, 02 Nov 2026 00:00:00 GMTDatabasespostgresqlauthenticationpg_hbadockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/redis-misconf-unable-to-persist-to-disk/https://ohsudo.com/articles/redis-misconf-unable-to-persist-to-disk/Fix Redis MISCONF "unable to persist to disk": read the log, then fix disk space, folder permissions or fork memory — and check the instance was not attacked.Mon, 02 Nov 2026 00:00:00 GMTDatabasesredisvalkeypersistencerdbmemorysecuritytroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/mysql-error-1045-access-denied/https://ohsudo.com/articles/mysql-error-1045-access-denied/Fix MySQL "ERROR 1045 Access denied for user": check the user@host account, the password, socket vs TCP, option files, and Docker init passwords.Sun, 01 Nov 2026 00:00:00 GMTDatabasesmysqlmariadbauthenticationusersdockertroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-duplicate-key-value-violates-unique-constraint/https://ohsudo.com/articles/postgresql-duplicate-key-value-violates-unique-constraint/Fix "duplicate key value violates unique constraint" in PostgreSQL: tell a real duplicate from a sequence that is out of sync, and fix both safely.Sun, 01 Nov 2026 00:00:00 GMTDatabasespostgresqlsequencesunique-constraintupserttroubleshootingcontact@ohsudo.com (OhSudo)https://ohsudo.com/articles/postgresql-permission-denied-for-table/https://ohsudo.com/articles/postgresql-permission-denied-for-table/Fix "ERROR: permission denied for table" in PostgreSQL: check what a role can do, grant the right privileges, and fix the schema, sequence and future-table cases.Sun, 01 Nov 2026 00:00:00 GMTDatabasespostgresqlpermissionsgranttroubleshootingcontact@ohsudo.com (OhSudo)