42P04 — Duplicate database

At a glance

42P04 (duplicate_database) means a database-management path found the requested name already in the cluster. It is a cluster-level name check, not a relation collision in the current database, and the CREATE and RENAME callers have different surrounding guards.

Meaning

In createdb, get_database_oid(dbname, true) checks the proposed database name and raises ERROR database "%s" already exists. RenameDatabase performs the same check against newname, after looking up the old database, checking ownership, and checking the CREATEDB privilege. The %s therefore names the requested database in CREATE or the new name in RENAME.

The utility dispatcher calls PreventInTransactionBlock(isTopLevel, "CREATE DATABASE") before it enters createdb. A CREATE DATABASE attempted inside an explicit transaction is therefore a separate transaction-block failure, not evidence that 42P04 was emitted. The RENAME path has its own old-name, owner, privilege, and new-name checks.

Diagnosis

Verify the target cluster and exact name in pg_database, including identifier folding and the possibility that another migration won a race. For CREATE, inspect the proposed name and template/owner prerequisites separately. For RENAME, inspect both old and new names plus ownership and CREATEDB; do not diagnose a missing old database or a privilege failure as 42P04.

Response

If the existing database is intended, make orchestration idempotent and inspect it rather than repeating CREATE DATABASE. Otherwise choose an unused name. Run CREATE DATABASE at top level, outside an explicit transaction block. For RENAME, choose an unused new name only after verifying the old database, ownership, CREATEDB, active sessions, dependencies, and cluster identity. If a RENAME ERROR occurs inside an explicit transaction, issue ROLLBACK before the next command, or ROLLBACK TO a savepoint created before the rename when the outer transaction must be retained. Drop or rename is not a generic repair for every 42P04.

Messages

The selected groups are explicit ERROR with database "%s" already exists: createdb supplies the requested name and RenameDatabase supplies the new name. The dispatcher’s PreventInTransactionBlock guard is source evidence for CREATE DATABASE’s separate transaction restriction, not another 42P04 message.

Versions

From 7.4 through 18.6 and 19beta3; that catalogue range is not a precise introduction claim. The selected CREATE, RENAME, and dispatcher guards are fixed 18.6 source paths; no runtime case was run.

Related

• 42P07
• 42P06
• 42710

Sources

• src.errcodes.42P04.18.6 — src/backend/utils/errcodes.txt line 379, fixed at 724edf9bde9d356724ad384a2e196edc3c9f80f7; SHA-256 6e8de346643ba84aa3c9c6a73360acfc7b2dfb89162c06c08ce9bf5bcd5bbcba (source).

• src.call.42P04.465a77b5605c341bc91f6990 — src/backend/commands/dbcommands.c lines 1393-1395, fixed at 724edf9bde9d356724ad384a2e196edc3c9f80f7; SHA-256 64b77d2197dce16eb1ad19d8168382459d621a03df0b00be157f7db39ca22acf (source).

• src.call.42P04.b0d1644def83c14a7504fec4 — src/backend/commands/dbcommands.c lines 1949-1951, fixed at 724edf9bde9d356724ad384a2e196edc3c9f80f7; SHA-256 64b77d2197dce16eb1ad19d8168382459d621a03df0b00be157f7db39ca22acf (source).

• src.call.42P04.create-tx-guard — src/backend/tcop/utility.c lines 769-773, fixed at 724edf9bde9d356724ad384a2e196edc3c9f80f7; SHA-256 7aae5d07628b6debf8456d1d4ea96f28912232192e56ea25773b4c4b61235a00 (source).

• src.calls.REL_18_6.42P04 — resolved core call groups; SHA-256 9ee8a0e81d8f0825c5c1ae45583439859a26e602bdd4ce2f2a62aa278867ccbf.

• authored evidence — source claims, message roles, and runtime boundary.