Table locking during backup

Hi,

I cannot reproduce some scenario I found in my PostgreSQL logs.

I have two connections/processes:

Process 24755 is standard pg_backup connection with:

.

BEGIN;
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ, READ ONLY

.

LOCK TABLE gm.tableabc;

.

COPY FROM gm.tableabc

Process 5969 is normal connection where I have:

LOG: proces 5969 still waiting for AccessExclusiveLock on relations
562888531 of database 16429 after 1000.066 ms

DETAILT: Process holding the lock: 24755. Wait queue: 5969

Query that is waiting (from proces 5969) is:

CREATE TEMP TABLE IF NOT EXISTS tableabc

(

Id BIGINT DEFAULT gm.top()

) INHERITS (gm.tableabc);

I cannot reproduce what pg_dump is doing that causes waiting on proces 5969
(which lock is acquired and why). When pg_dump ends lock is released and
proces 5969 continues.

I know that doing in two parallel connections:

BEGIN;

CREATE TEMP TABLE IF NOT EXISTS tableabc

(

Id BIGINT DEFAULT gm.top()

) INHERITS (gm.tableabc);

causes waiting state on second connection until the first finished, but
pg_dump connection is read only.

Could you suggest me which part of pg_dump (which query) might cause that
behaviour.

Artur Zając