Hi, I noticed that since PostgreSQL 12, Tid scan increments value of
pg_stat_all_tables.seq_scan. (but not seq_tup_read)
The following is an example.
CREATE TABLE t (c int);
INSERT INTO t SELECT 1;
SET enable_seqscan to off;
(v12 -)
=# EXPLAIN ANALYZE SELECT * FROM t WHERE ctid = '(0,1)';
QUERY PLAN
-------------------------------------------------------------------------------------------
Tid Scan on t (cost=0.00..4.01 rows=1 width=4) (actual
time=0.034..0.035 rows=1 loops=1)
TID Cond: (ctid = '(0,1)'::tid)
Planning Time: 0.341 ms
Execution Time: 0.059 ms
(4 rows)
=# SELECT seq_scan, seq_tup_read FROM pg_stat_user_tables WHERE relname = 't';
seq_scan | seq_tup_read
----------+--------------
1 | 0
(1 row)
(- v11)
=# EXPLAIN ANALYZE SELECT * FROM t WHERE ctid = '(0,1)';
QUERY PLAN
-------------------------------------------------------------------------------------------
Tid Scan on t (cost=0.00..4.01 rows=1 width=4) (actual
time=0.026..0.027 rows=1 loops=1)
TID Cond: (ctid = '(0,1)'::tid)
Planning Time: 1.003 ms
Execution Time: 0.068 ms
(4 rows)
postgres=# SELECT seq_scan, seq_tup_read FROM pg_stat_user_tables
WHERE relname = 't';
seq_scan | seq_tup_read
----------+--------------
0 | 0
(1 row)
Exactly, this change occurred from following commit.
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=147e3722f7e531f15ba389a4d518efe8cd0bd736)
I think, from this commit, TidListEval() came to call
table_beginscan() , so this increments would be happen.
I'm not sure this change whether intention or not, it can confuse some users.
Best regards,
--
NTT Open Source Software Center
Tatsuhito Kasahara
