InitTempTableNamespace.md

InitTempTableNamespace

Location

src/backend/catalog/namespace.c:4390-4511

Overview

Initializes the temporary table namespace on first use in a backend, creating both temp and toast namespaces with proper permissions and cleanup.

Definition

static void
InitTempTableNamespace(void)

Detailed Description

InitTempTableNamespace performs the complex initialization of PostgreSQL's temporary table namespace system for a backend process. The function handles multiple critical aspects:

Permission and State Validation:

• Verifies the current user has ACL_CREATE_TEMP privileges on the database
• Prevents temp table creation during Hot Standby recovery mode
• Blocks temp table creation in parallel worker processes

Namespace Creation and Management:

• Creates a uniquely named temp namespace (pg_temp_N) based on the backend's MyProcNumber
• If the namespace already exists (from a crashed previous session), cleans out existing temporary relations
• Creates a corresponding toast namespace (pg_toast_temp_N) for TOAST tables
• Sets namespace ownership to the bootstrap superuser with restrictive permissions

State Management:

• Updates global variables (myTempNamespace, myTempToastNamespace) to track the namespaces
• Marks the process as owning the namespace via MyProc->tempNamespaceId
• Records the subtransaction ID for proper cleanup handling
• Invalidates search path caches since the namespace list has changed

Parameters / Member Variables

Dependencies

• Functions called/Symbols referenced:
  • NAMEDATALEN (constant)
  • object_aclcheck
  • ACL_CREATE_TEMP
  • get_database_name
  • RecoveryInProgress
  • IsParallelWorker
  • get_namespace_oid
  • NamespaceCreate
  • CommandCounterIncrement
  • RemoveTempRelations
  • InvalidSubTransactionId
  • GetCurrentSubTransactionId
• Called from (representative examples):
  • AccessTempTableNamespace

Notes and Other Information

• This is a static function only accessible within namespace.c
• Uses BOOTSTRAP_SUPERUSERID as the owner to ensure security isolation between backends
• The namespace naming scheme (pg_temp_N) ensures uniqueness across concurrent backends
• Command counter increments ensure namespace visibility within the same transaction
• Critical for transaction cleanup via AtEOXact_Namespace through the recorded subtransaction ID
• Implements lazy initialization - namespaces are only created when actually needed
• Handles crash recovery by cleaning up leftover temporary relations from previous sessions

Simplified Source

static void
InitTempTableNamespace(void) {
    char namespaceName[NAMEDATALEN];
    Oid namespaceId;
    Oid toastspaceId;

    Assert(!OidIsValid(myTempNamespace));

    // Check permissions for creating temp tables
    if (object_aclcheck(DatabaseRelationId, MyDatabaseId, GetUserId(), ACL_CREATE_TEMP) != ACLCHECK_OK)
        ereport(ERROR, (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                errmsg("permission denied to create temporary tables")));

    // Prevent temp tables during recovery or parallel operations
    if (RecoveryInProgress())
        ereport(ERROR, (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
                errmsg("cannot create temporary tables during recovery")));

    if (IsParallelWorker())
        ereport(ERROR, (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
                errmsg("cannot create temporary tables during parallel operation")));

    // Create namespace name: pg_temp_N
    snprintf(namespaceName, sizeof(namespaceName), "pg_temp_%d", MyProcNumber);

    // Check if namespace exists
    namespaceId = get_namespace_oid(namespaceName, true);
    if (!OidIsValid(namespaceId)) {
        // Create new temp namespace owned by superuser
        namespaceId = NamespaceCreate(namespaceName, BOOTSTRAP_SUPERUSERID, true);
        CommandCounterIncrement();
    } else {
        // Clean up existing namespace from crashed session
        RemoveTempRelations(namespaceId);
    }

    // Create corresponding toast namespace: pg_toast_temp_N
    snprintf(namespaceName, sizeof(namespaceName), "pg_toast_temp_%d", MyProcNumber);
    toastspaceId = get_namespace_oid(namespaceName, true);
    if (!OidIsValid(toastspaceId)) {
        toastspaceId = NamespaceCreate(namespaceName, BOOTSTRAP_SUPERUSERID, true);
        CommandCounterIncrement();
    }

    // Set global state variables
    myTempNamespace = namespaceId;
    myTempToastNamespace = toastspaceId;
    MyProc->tempNamespaceId = namespaceId;
    myTempNamespaceSubID = GetCurrentSubTransactionId();

    // Invalidate search path caches
    baseSearchPathValid = false;
    searchPathCacheValid = false;
}