from fixtures.log_helper import log from fixtures.neon_fixtures import NeonEnv, fork_at_current_lsn # # Test that the VM bit is cleared correctly at a HEAP_DELETE and # HEAP_UPDATE record. # def test_vm_bit_clear(neon_simple_env: NeonEnv): env = neon_simple_env env.neon_cli.create_branch("test_vm_bit_clear", "empty") endpoint = env.endpoints.create_start("test_vm_bit_clear") log.info("postgres is running on 'test_vm_bit_clear' branch") pg_conn = endpoint.connect() cur = pg_conn.cursor() # Install extension containing function needed for test cur.execute("CREATE EXTENSION neon_test_utils") # Create a test table for a few different scenarios and freeze it to set the VM bits. cur.execute("CREATE TABLE vmtest_delete (id integer PRIMARY KEY)") cur.execute("INSERT INTO vmtest_delete VALUES (1)") cur.execute("VACUUM FREEZE vmtest_delete") cur.execute("CREATE TABLE vmtest_hot_update (id integer PRIMARY KEY, filler text)") cur.execute("INSERT INTO vmtest_hot_update VALUES (1, 'x')") cur.execute("VACUUM FREEZE vmtest_hot_update") cur.execute("CREATE TABLE vmtest_cold_update (id integer PRIMARY KEY)") cur.execute("INSERT INTO vmtest_cold_update SELECT g FROM generate_series(1, 1000) g") cur.execute("VACUUM FREEZE vmtest_cold_update") cur.execute( "CREATE TABLE vmtest_cold_update2 (id integer PRIMARY KEY, filler text) WITH (fillfactor=100)" ) cur.execute("INSERT INTO vmtest_cold_update2 SELECT g, '' FROM generate_series(1, 1000) g") cur.execute("VACUUM FREEZE vmtest_cold_update2") # DELETE and UPDATE the rows. cur.execute("DELETE FROM vmtest_delete WHERE id = 1") cur.execute("UPDATE vmtest_hot_update SET filler='x' WHERE id = 1") cur.execute("UPDATE vmtest_cold_update SET id = 5000 WHERE id = 1") # Clear the VM bit on the last page with an INSERT. Then clear the VM bit on # the page where row 1 is (block 0), by doing an UPDATE. The UPDATE is a # cold update, and the new tuple goes to the last page, which already had # its VM bit cleared. The point is that the UPDATE *only* clears the VM bit # on the page containing the old tuple. We had a bug where we got the old # and new pages mixed up, and that only shows up when one of the bits is # cleared, but not the other one. cur.execute("INSERT INTO vmtest_cold_update2 VALUES (9999, 'x')") # Clears the VM bit on the old page cur.execute("UPDATE vmtest_cold_update2 SET id = 5000, filler=repeat('x', 200) WHERE id = 1") # Branch at this point, to test that later fork_at_current_lsn(env, endpoint, "test_vm_bit_clear_new", "test_vm_bit_clear") # Clear the buffer cache, to force the VM page to be re-fetched from # the page server cur.execute("SELECT clear_buffer_cache()") # Check that an index-only scan doesn't see the deleted row. If the # clearing of the VM bit was not replayed correctly, this would incorrectly # return deleted row. cur.execute( """ set enable_seqscan=off; set enable_indexscan=on; set enable_bitmapscan=off; """ ) cur.execute("SELECT id FROM vmtest_delete WHERE id = 1") assert cur.fetchall() == [] cur.execute("SELECT id FROM vmtest_hot_update WHERE id = 1") assert cur.fetchall() == [(1,)] cur.execute("SELECT id FROM vmtest_cold_update WHERE id = 1") assert cur.fetchall() == [] cur.execute("SELECT id FROM vmtest_cold_update2 WHERE id = 1") assert cur.fetchall() == [] cur.close() # Check the same thing on the branch that we created right after the DELETE # # As of this writing, the code in smgrwrite() creates a full-page image whenever # a dirty VM page is evicted. If the VM bit was not correctly cleared by the # earlier WAL record, the full-page image hides the problem. Starting a new # server at the right point-in-time avoids that full-page image. endpoint_new = env.endpoints.create_start("test_vm_bit_clear_new") log.info("postgres is running on 'test_vm_bit_clear_new' branch") pg_new_conn = endpoint_new.connect() cur_new = pg_new_conn.cursor() cur_new.execute( """ set enable_seqscan=off; set enable_indexscan=on; set enable_bitmapscan=off; """ ) cur_new.execute("SELECT id FROM vmtest_delete WHERE id = 1") assert cur_new.fetchall() == [] cur_new.execute("SELECT id FROM vmtest_hot_update WHERE id = 1") assert cur_new.fetchall() == [(1,)] cur_new.execute("SELECT id FROM vmtest_cold_update WHERE id = 1") assert cur_new.fetchall() == [] cur_new.execute("SELECT id FROM vmtest_cold_update2 WHERE id = 1") assert cur_new.fetchall() == [] # # Test that the ALL_FROZEN VM bit is cleared correctly at a HEAP_LOCK # record. # def test_vm_bit_clear_on_heap_lock(neon_simple_env: NeonEnv): env = neon_simple_env env.neon_cli.create_branch("test_vm_bit_clear_on_heap_lock", "empty") endpoint = env.endpoints.create_start( "test_vm_bit_clear_on_heap_lock", config_lines=[ "log_autovacuum_min_duration = 0", # Perform anti-wraparound vacuuming aggressively "autovacuum_naptime='1 s'", "autovacuum_freeze_max_age = 1000000", ], ) pg_conn = endpoint.connect() cur = pg_conn.cursor() # Install extension containing function needed for test cur.execute("CREATE EXTENSION neon_test_utils") cur.execute("SELECT pg_switch_wal()") # Create a test table and freeze it to set the all-frozen VM bit on all pages. cur.execute("CREATE TABLE vmtest_lock (id integer PRIMARY KEY)") cur.execute("INSERT INTO vmtest_lock SELECT g FROM generate_series(1, 50000) g") cur.execute("VACUUM FREEZE vmtest_lock") # Lock a row. This clears the all-frozen VM bit for that page. cur.execute("SELECT * FROM vmtest_lock WHERE id = 40000 FOR UPDATE") # Remember the XID. We will use it later to verify that we have consumed a lot of # XIDs after this. cur.execute("select pg_current_xact_id()") locking_xid = cur.fetchall()[0][0] # Stop and restart postgres, to clear the buffer cache. # # NOTE: clear_buffer_cache() will not do, because it evicts the dirty pages # in a "clean" way. Our neon extension will write a full-page image of the VM # page, and we want to avoid that. endpoint.stop() endpoint.start() pg_conn = endpoint.connect() cur = pg_conn.cursor() cur.execute("select xmin, xmax, * from vmtest_lock where id = 40000 ") tup = cur.fetchall() xmax_before = tup[0][1] # Consume a lot of XIDs, so that anti-wraparound autovacuum kicks # in and the clog gets truncated. We set autovacuum_freeze_max_age to a very # low value, so it doesn't take all that many XIDs for autovacuum to kick in. for i in range(1000): cur.execute( """ CREATE TEMP TABLE othertable (i int) ON COMMIT DROP; do $$ begin for i in 1..100000 loop -- Use a begin-exception block to generate a new subtransaction on each iteration begin insert into othertable values (i); exception when others then raise 'not expected %', sqlerrm; end; end loop; end; $$; """ ) cur.execute("select xmin, xmax, * from vmtest_lock where id = 40000 ") tup = cur.fetchall() log.info(f"tuple = {tup}") xmax = tup[0][1] assert xmax == xmax_before if i % 50 == 0: cur.execute("select datfrozenxid from pg_database where datname='postgres'") datfrozenxid = cur.fetchall()[0][0] if datfrozenxid > locking_xid: break cur.execute("select pg_current_xact_id()") curr_xid = cur.fetchall()[0][0] assert int(curr_xid) - int(locking_xid) >= 100000 # Now, if the VM all-frozen bit was not correctly cleared on # replay, we will try to fetch the status of the XID that was # already truncated away. # # ERROR: could not access status of transaction 1027 cur.execute("select xmin, xmax, * from vmtest_lock where id = 40000 for update") tup = cur.fetchall() log.info(f"tuple = {tup}")