PostgreSQL prevents automatic vacuuming of temporary tables since they are session-specific. Manual VACUUM calls within the same session are allowed, or you can use TRUNCATE for faster cleanup without requiring maintenance.
Temporary tables in PostgreSQL are session-scoped objects that only the creating database connection can see. Because the autovacuum daemon cannot access temporary tables, attempting an automatic VACUUM or running VACUUM from outside the session that created the table results in this error. This is a safety restriction to prevent cross-session interference with temporary objects. The error typically occurs when scripts or tools attempt to maintain a temporary table without accounting for the session-visibility constraint. Unlike regular tables, temporary tables have unique maintenance requirements because their data is automatically cleaned up when the session ends.
Check if the table is defined as TEMPORARY or TEMP in your CREATE TABLE statement:
CREATE TEMPORARY TABLE my_temp_table (
id SERIAL PRIMARY KEY,
data TEXT
);You can also query the system catalog to confirm:
SELECT tablename, relpersistence
FROM pg_tables
JOIN pg_class ON pg_tables.tablename = pg_class.relname
WHERE tablename = 'my_temp_table';
-- relpersistence = 't' means temporaryIf you must vacuum the temporary table, do so from within the same session that created it:
-- From the session that created the temporary table:
VACUUM my_temp_table;
ANALYZE my_temp_table; -- optional, updates query planner statisticsDo not attempt to run this from a separate connection or administrative session.
For temporary tables where you need to regularly clear data, TRUNCATE is more efficient than DELETE followed by VACUUM:
TRUNCATE my_temp_table; -- Much faster, reclaims space immediatelyThis is particularly useful in stored procedures or applications that reuse temporary tables multiple times within a session.
For frequently-reset temporary tables, use the ON COMMIT clause to automatically clear data:
CREATE TEMPORARY TABLE my_temp_table (
id SERIAL PRIMARY KEY,
data TEXT
) ON COMMIT DELETE ROWS; -- Automatically TRUNCATE at transaction endThis eliminates the need for manual VACUUM or TRUNCATE calls and prevents dead row accumulation.
If you have scripts that VACUUM all tables, filter out temporary ones:
-- Vacuum only permanent tables
VACUUM ANALYZE
WHERE relpersistence != 't';
-- Better approach: Use SELECT query to build dynamic VACUUM list
SELECT 'VACUUM ANALYZE ' || tablename || ';'
FROM pg_tables
WHERE schemaname NOT IN ('pg_catalog', 'information_schema')
AND relpersistence != 't'; -- Exclude temporary tablesTemporary tables are automatically cleaned up when their creating session ends, so VACUUM is only necessary for long-lived sessions that repeatedly modify the same temporary table over extended periods. For short-lived temporary tables used in quick operations, VACUUM is unnecessary overhead. If orphaned temporary tables are causing XID wraparound issues, consider implementing session cleanup mechanisms or reducing the lifetime of temporary tables. Some ORMs and database connection pools may create phantom temporary tables if sessions are not properly closed; ensure your application properly closes all database connections to prevent this scenario.
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