Open jefft opened 7 years ago
Hi Jeff,
Thanks for sharing the test cases, the where clause should get pushed down for every iteration. We will try and investigate this issue asap and revert back on this thread...
-- Ahsan
Let me add to this. I have noted the same behavior on Postgres 9.6. It is not restricted to for loops, but simple invocations also cause this. For instance, the following function returns quickly 5 times, but on the 6th time and subsequently runs slowly.
CREATE OR REPLACE function ess.get_mysql_max_prid(_min_prid bigint) RETURNS bigint AS $$
DECLARE
max_prid bigint;
BEGIN
IF _min_prid IS NOT NULL THEN
RAISE NOTICE 'prid is %',_min_prid;
max_prid := max(prid) FROM mysql_extservice_all WHERE prid >= _min_prid;
ELSE
RAISE NOTICE 'min_prid is null';
SELECT max(prid) FROM mysql_extservice_all INTO max_prid;
END IF;
RETURN max_prid;
END;
$$ language 'plpgsql';
Immediately after creation, the following all return in less that 1 second
ess=> select * from ess.get_mysql_max_prid(6328025);
NOTICE: prid is 6328025
get_mysql_max_prid
--------------------
6348494
(1 row)
ess=> select * from ess.get_mysql_max_prid(6328025);
NOTICE: prid is 6328025
get_mysql_max_prid
--------------------
6348495
(1 row)
ess=> select * from ess.get_mysql_max_prid(6328025);
NOTICE: prid is 6328025
get_mysql_max_prid
--------------------
6348498
(1 row)
ess=> select * from ess.get_mysql_max_prid(6328025);
NOTICE: prid is 6328025
get_mysql_max_prid
--------------------
6348500
(1 row)
ess=> select * from ess.get_mysql_max_prid(6328025);
NOTICE: prid is 6328025
get_mysql_max_prid
--------------------
6348509
(1 row)
Eventually, returns, but takes approximately 40 seconds. All subsequent invocations also take this long. Re-defining the stored procedure resets the behavior to working 5 times quickly.
ess=> select * from ess.get_mysql_max_prid(6328025);
NOTICE: prid is 6328025
--------------------
6348513
(1 row)
@waTeim @jefft Giant kudos for figuring out this behavior! 🎆
I just ended up using materialized views and only issuing simple SELECT
statements with mysql_fdw
because it was so buggy with pushing quals down causing queries to sporadically fail (JOIN
s were very problematic).
This is a huge issue and needs to be fixed. I pity the fool using mysql_fdw
in production without catching this in development!
This is an important issue, we will try and fix this on priority...
On Sun, Jan 8, 2017 at 4:30 AM, Jeffrey notifications@github.com wrote:
@waTeim https://github.com/waTeim @jefft https://github.com/jefft Giant kudos for figuring out this behavior! 🎆
I just ended up using MATERIALIZED VIEWS and only issuing simple SELECT statements with mysql_fdw because it was so buggy with pushing quals down causing queries to sporadically fail.
This is a huge issue and needs to be fixed. I pity the fool using mysql_fdw in production without catching this in development!
— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/EnterpriseDB/mysql_fdw/issues/118#issuecomment-271117676, or mute the thread https://github.com/notifications/unsubscribe-auth/AHmqpLtKg_H5E9u7hxDCA_HX9_jxIdgfks5rQCAfgaJpZM4KEly9 .
-- Ahsan Hadi Snr Director Product Development EnterpriseDB Corporation The Enterprise Postgres Company
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Hi, We are finally getting around to looking at this issue. It seems that the planner stops pushing down the where clause after a certain number of iterations. The same behaviour is reproducible with postgres_fdw using a postgres foreign server. We will continue to look at this problem and keep your posted...
@jefft Push down support after 5 calls is supported now, can you please check.
@jefft: Can you check or close this issue? I reviewed the fix and it looks like the test cases cover the reported issue.
@ibrarahmad, @jmealo, using latest from git, instead of slow queries I now get outright breakage after the fifth query:
postgres@jturner-desktop:~$ psql -tAq testdb < slowloop.sql
NOTICE: Found user Bob
NOTICE: Found user Fred
NOTICE: Found user Sally
NOTICE: Found user Mary
NOTICE: Found user Jimmy
ERROR: failed to execute the MySQL query:
You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '?))' at line 1
CONTEXT: SQL statement "select name from users where id=x"
PL/pgSQL function test() line 6 at SQL statement
postgres@jturner-desktop:~$
In mysql.log I see:
170504 11:41:45 2 Connect root@localhost as anonymous on testdb
2 Query SET sql_mode='ANSI_QUOTES'
2 Query EXPLAIN SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 1))
2 Query SET time_zone = '+00:00'
2 Query SET sql_mode='ANSI_QUOTES'
2 Prepare SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 1))
2 Execute SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 1))
2 Close stmt
2 Query SET sql_mode='ANSI_QUOTES'
2 Query EXPLAIN SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 2))
2 Query SET time_zone = '+00:00'
2 Query SET sql_mode='ANSI_QUOTES'
2 Prepare SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 2))
2 Execute SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 2))
2 Close stmt
2 Query SET sql_mode='ANSI_QUOTES'
2 Query EXPLAIN SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 3))
2 Query SET time_zone = '+00:00'
2 Query SET sql_mode='ANSI_QUOTES'
2 Prepare SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 3))
2 Execute SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 3))
2 Close stmt
2 Query SET sql_mode='ANSI_QUOTES'
2 Query EXPLAIN SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 4))
2 Query SET time_zone = '+00:00'
2 Query SET sql_mode='ANSI_QUOTES'
2 Prepare SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 4))
2 Execute SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 4))
2 Close stmt
2 Query SET sql_mode='ANSI_QUOTES'
2 Query EXPLAIN SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 5))
2 Query SET time_zone = '+00:00'
2 Query SET sql_mode='ANSI_QUOTES'
2 Prepare SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 5))
2 Execute SELECT `name` FROM `testdb`.`users` WHERE ((`id` = 5))
2 Close stmt
2 Query SET sql_mode='ANSI_QUOTES'
2 Query EXPLAIN SELECT `name` FROM `testdb`.`users` WHERE ((`id` = ?))
2 Quit
Here is the full series of commands for replicating, tested in a clean Ubuntu 16.04.2 (full console output in transcript.txt):
apt update
apt install -y postgresql-9.5 mariadb-server mariadb-client libmysqlclient-dev postgresql-server-dev-9.5 make gcc
perl -i -pe 's/^#general_log/general_log/g' /etc/mysql/mariadb.conf.d/50-server.cnf; systemctl restart mysql # turn on mysql.log
# Change 'root' auth from socket to password so it works from psql.
echo "grant all privileges on *.* to 'root'@'localhost' identified by 'secret'" | mysql
cat <<'EOF' > ~/.my.cnf
[mysql]
user=root
password=secret
EOF
mkdir -p ~/src/github.com/EnterpriseDB
git clone https://github.com/EnterpriseDB/mysql_fdw.git ~/src/github.com/EnterpriseDB/mysql_fdw # At commit 86ad3af
cd src/github.com/EnterpriseDB/mysql_fdw/
sudo make USE_PGXS=1 install
cat <<'EOF' > /tmp/testdb_mysql.sql
DROP DATABASE if exists testdb ;
CREATE DATABASE testdb;
USE testdb;
CREATE TABLE users (
id integer,
name text,
photo blob
);
INSERT INTO `users` VALUES (1,'Bob','xxxx');
INSERT INTO `users` VALUES (2,'Fred','yyyyy');
INSERT INTO `users` VALUES (3,'Sally','zzzz');
INSERT INTO `users` VALUES (4,'Mary','qzqzqz');
INSERT INTO `users` VALUES (5,'Jimmy','abcabc');
INSERT INTO `users` VALUES (6,'User6','12345');
INSERT INTO `users` VALUES (7,'User7','12346');
INSERT INTO `users` VALUES (8,'User8','12347');
INSERT INTO `users` VALUES (9,'User9','12348');
INSERT INTO `users` VALUES (10,'User10','12349');
EOF
cat <<'EOF' > /tmp/testdb_psql.sql
CREATE DATABASE testdb;
GRANT usage ON SCHEMA PUBLIC TO postgres;
\c testdb;
CREATE EXTENSION mysql_fdw;
CREATE SERVER mysql_server FOREIGN DATA WRAPPER mysql_fdw OPTIONS (host '127.0.0.1', port '3306', use_remote_estimate 'true');
CREATE USER MAPPING FOR postgres SERVER mysql_server OPTIONS (username 'root', password 'secret');
GRANT USAGE ON FOREIGN SERVER mysql_server to postgres;
IMPORT FOREIGN SCHEMA testdb FROM SERVER mysql_server INTO public;
select * from users;
EOF
su - postgres -c psql < /tmp/testdb_psql.sql
cat <<'EOF' > /tmp/slowloop.sql
create or replace function test() returns void as $$
DECLARE
n varchar;
BEGIN
FOR x IN 1..10 LOOP
select name into n from users where id=x;
raise notice 'Found user %', n;
end loop;
return;
END
$$ LANGUAGE plpgsql;
SELECT test();
EOF
su - postgres -c 'psql testdb' < /tmp/slowloop.sql
Hi @ahsanhadi @jefft , Has this issue been fixed? I'm the fool using mysql_fdw in production without catching this issue in development!
I use postgres12.6 & mysql_fdw 2.5.5
This is my table definition: database diagram
--PG
CREATE TABLE DDTINTO_MASTER (
AC_DATE int NOT NULL DEFAULT 0,
AC_NO varchar(12) NOT NULL DEFAULT '',
CCY varchar(3) NOT NULL DEFAULT '',
QUALIFIER char(1) NOT NULL DEFAULT '',
DEP decimal(16, 2) NOT NULL DEFAULT 0.00
....
TS TIMESTAMP WITHOUT TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP
) PARTITION BY RANGE (AC_DATE);
CREATE TABLE ddtinto_201909 PARTITION OF DDTINTO_MASTER FOR VALUES FROM (10000101) TO (20191001);
CREATE TABLE ddtinto_201910 PARTITION OF DDTINTO_MASTER FOR VALUES FROM (20191001) TO (20191101);
...
CREATE INDEX ddtinto_pk on DDTINTO_MASTER (ac_no, ccy, qualifier, ac_date);
CREATE VIEW DDTINTO AS
SELECT * FROM DDTINTO_CURRENT
UNION ALL
SELECT * FROM DDTINTO_MASTER;
--MySQL
create view view_ddtinto_current
as
select * from ddtinto
where ac_date >= 20210401;
Sometimes , FDW can push all where clauses to MySQL, sometimes can only push part of the where caluses. Here is the latter's explain plan, Remote query lack 2 where clauses: ac_no and ccy
2021-06-04 00:22:10.311 CST [2695] LOG: duration: 928091.882 ms execute S_8: SELECT TRIM(AC_NO) AC_NO
, TRIM(CCY) CCY
, AC_DATE
, DEP
, QUALIFIER
FROM DDTINTO
WHERE QUALIFIER IN ('A', 'C')
and AC_NO = $1
and CCY = $2
and AC_DATE >= $3
and AC_DATE <= $4
ORDER BY AC_DATE DESC
limit $5
2021-06-04 00:22:10.311 CST [2695] DETAIL: parameters: $1 = '889005309160', $2 = 'HKD', $3 = '20210306', $4 = '20210604', $5 = '180'
2021-06-04 00:22:10.312 CST [2695] LOG: duration: 928091.872 ms plan:
Query Text: SELECT TRIM(AC_NO) AC_NO
, TRIM(CCY) CCY
, AC_DATE
, DEP
, QUALIFIER
FROM DDTINTO
WHERE QUALIFIER IN ('A', 'C')
and AC_NO = $1
and CCY = $2
and AC_DATE >= $3
and AC_DATE <= $4
ORDER BY AC_DATE DESC
limit $5
Limit (cost=1273.68..1273.94 rows=102 width=94) (actual time=928091.796..928091.825 rows=88 loops=1)
Output: (btrim((ddtinto_current.ac_no)::text)), (btrim((ddtinto_current.ccy)::text)), ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Buffers: shared hit=64
-> Sort (cost=1273.68..1276.23 rows=1020 width=94) (actual time=928091.794..928091.806 rows=88 loops=1)
Output: (btrim((ddtinto_current.ac_no)::text)), (btrim((ddtinto_current.ccy)::text)), ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Sort Key: ddtinto_current.ac_date DESC
Sort Method: quicksort Memory: 31kB
Buffers: shared hit=64
-> Result (cost=25.00..1222.71 rows=1020 width=94) (actual time=231239.514..928091.626 rows=88 loops=1)
Output: btrim((ddtinto_current.ac_no)::text), btrim((ddtinto_current.ccy)::text), ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Buffers: shared hit=64
-> Append (cost=25.00..1207.41 rows=1020 width=87) (actual time=231239.509..928091.454 rows=88 loops=1)
Buffers: shared hit=64
Subplans Removed: 18
-> Foreign Scan on public.ddtinto_current (cost=25.00..1025.00 rows=1000 width=88) (actual time=231239.507..928091.234 rows=33 loops=1)
Output: ddtinto_current.ac_no, ddtinto_current.ccy, ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Filter: (((ddtinto_current.ac_no)::text = ($1)::text) AND ((ddtinto_current.ccy)::text = ($2)::text))
Rows Removed by Filter: 34667775
Remote server startup cost: 25
Remote query: SELECT `ac_date`, `ac_no`, `ccy`, `qualifier`, `dep` FROM `ocbs387`.`view_ddtinto_current` WHERE (`qualifier` IN ('A', 'C')) AND ((`ac_date` >= ?)) AND ((`ac_date` <= ?))
-> Index Scan using ddtinto_202103_ac_no_ccy_qualifier_ac_date_idx on public.ddtinto_202103 (cost=0.56..9.10 rows=1 width=26) (actual time=0.051..0.089 rows=25 loops=1)
Output: ddtinto_202103.ac_no, ddtinto_202103.ccy, ddtinto_202103.ac_date, ddtinto_202103.dep, ddtinto_202103.qualifier
Index Cond: (((ddtinto_202103.ac_no)::text = ($1)::text) AND ((ddtinto_202103.ccy)::text = ($2)::text) AND (ddtinto_202103.ac_date >= $3) AND (ddtinto_202103.ac_date <= $4))
Filter: (ddtinto_202103.qualifier = ANY ('{A,C}'::bpchar[]))
Buffers: shared hit=29
-> Index Scan using ddtinto_202104_ac_no_ccy_qualifier_ac_date_idx on public.ddtinto_202104 (cost=0.56..9.08 rows=1 width=26) (actual time=0.022..0.063 rows=30 loops=1)
Output: ddtinto_202104.ac_no, ddtinto_202104.ccy, ddtinto_202104.ac_date, ddtinto_202104.dep, ddtinto_202104.qualifier
Index Cond: (((ddtinto_202104.ac_no)::text = ($1)::text) AND ((ddtinto_202104.ccy)::text = ($2)::text) AND (ddtinto_202104.ac_date >= $3) AND (ddtinto_202104.ac_date <= $4))
Filter: (ddtinto_202104.qualifier = ANY ('{A,C}'::bpchar[]))
Rows Removed by Filter: 1
Buffers: shared hit=35
Hi @MondayLiu,
The original issue reported above seems to be fixed however, I suspect some other issue by looking at your test case. I could not reproduce this exact issue at my end. It would be good if you share exact DDLs from PG and MySQL with sample data from PG and MySQL to reproduce the issue.
Moreover, can you please confirm on below points:
Thanks and Regards, Suraj Kharage
Hi @surajkharage19 , Thanks for response! After I reproduce in development! I'll new another issue. So far, only the following replies can be made:
The probability of 97/1020 leads to partial where clause pushdown.
Here is complete where clause pushdown:
2021-06-04 00:06:28.015 CST [2617] LOG: duration: 741.972 ms plan:
Query Text: SELECT TRIM(AC_NO) AC_NO
, TRIM(CCY) CCY
, AC_DATE
, DEP
, QUALIFIER
FROM DDTINTO
WHERE QUALIFIER IN ('A', 'C')
and AC_NO = $1
and CCY = $2
and AC_DATE >= $3
and AC_DATE <= $4
ORDER BY AC_DATE DESC
limit $5
Limit (cost=1366.36..1366.81 rows=180 width=93) (actual time=741.891..741.921 rows=89 loops=1)
Output: (btrim((ddtinto_current.ac_no)::text)), (btrim((ddtinto_current.ccy)::text)), ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Buffers: shared hit=22 read=43 dirtied=38
-> Sort (cost=1366.36..1369.02 rows=1065 width=93) (actual time=741.889..741.902 rows=89 loops=1)
Output: (btrim((ddtinto_current.ac_no)::text)), (btrim((ddtinto_current.ccy)::text)), ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Sort Key: ddtinto_current.ac_date DESC
Sort Method: quicksort Memory: 31kB
Buffers: shared hit=22 read=43 dirtied=38
-> Result (cost=25.00..1321.14 rows=1065 width=93) (actual time=45.109..741.696 rows=89 loops=1)
Output: btrim((ddtinto_current.ac_no)::text), btrim((ddtinto_current.ccy)::text), ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Buffers: shared hit=22 read=43 dirtied=38
-> Append (cost=25.00..1305.17 rows=1065 width=84) (actual time=45.104..741.483 rows=89 loops=1)
Buffers: shared hit=22 read=43 dirtied=38
-> Foreign Scan on public.ddtinto_current (cost=25.00..1025.00 rows=1000 width=88) (actual time=45.102..45.129 rows=33 loops=1)
Output: ddtinto_current.ac_no, ddtinto_current.ccy, ddtinto_current.ac_date, ddtinto_current.dep, ddtinto_current.qualifier
Remote server startup cost: 25
Remote query: SELECT `ac_date`, `ac_no`, `ccy`, `qualifier`, `dep` FROM `ocbs387`.`view_ddtinto_current` WHERE (`qualifier` IN ('A', 'C')) AND ((`ac_date` >= 20210306)) AND ((`ac_date` <= 20210604)) AND ((`ac_no` = '883005072877')) AND ((`ccy` = 'HKD'))
-> Index Scan using ddtinto_202103_ac_no_ccy_qualifier_ac_date_idx on public.ddtinto_202103 (cost=0.56..129.39 rows=31 width=26) (actual time=8.999..356.128 rows=26 loops=1)
Output: ddtinto_202103.ac_no, ddtinto_202103.ccy, ddtinto_202103.ac_date, ddtinto_202103.dep, ddtinto_202103.qualifier
Index Cond: (((ddtinto_202103.ac_no)::text = '883005072877'::text) AND ((ddtinto_202103.ccy)::text = 'HKD'::text) AND (ddtinto_202103.ac_date >= 20210306) AND (ddtinto_202103.ac_date <= 20210604))
Filter: (ddtinto_202103.qualifier = ANY ('{A,C}'::bpchar[]))
Buffers: shared hit=5 read=25 dirtied=23
-> Index Scan using ddtinto_202104_ac_no_ccy_qualifier_ac_date_idx on public.ddtinto_202104 (cost=0.56..145.46 rows=34 width=26) (actual time=30.783..340.156 rows=30 loops=1)
Output: ddtinto_202104.ac_no, ddtinto_202104.ccy, ddtinto_202104.ac_date, ddtinto_202104.dep, ddtinto_202104.qualifier
Index Cond: (((ddtinto_202104.ac_no)::text = '883005072877'::text) AND ((ddtinto_202104.ccy)::text = 'HKD'::text) AND (ddtinto_202104.ac_date >= 20210306) AND (ddtinto_202104.ac_date <= 20210604))
Filter: (ddtinto_202104.qualifier = ANY ('{A,C}'::bpchar[]))
Rows Removed by Filter: 1
Buffers: shared hit=17 read=18 dirtied=15
500 milliseconds SQL.
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PG holds historical data and MySQL holds current data.There are 80 million records in total. Two-thirds are in PG.
All 5 where caluse in SQL are required.
Thanks and Regards, Monday Liu
Thanks for sharing the information.
This issue seems occurring randomly, not following any pattern. There might be chances that the planner is doing some optimization based on parameter values. I would appreciate it if you could provide the exact test case to reproduce this issue and that will help us with further troubleshooting. Also, are you observing the same behavior when you execute the above query (with exact values) on psql?
Hi,
_TL;DR: mysqlfdw queries can become dramatically slower within PL/pgSQL FOR loops, due to the query optimizer eliminating the WHERE clause push-down.
I'm trying to import MySQL data into Postgres 9.5, using PL/pgSQL. The MySQL tables are large, and so the WHERE clause push-down is crucial -- otherwise
select * from bigtable where id=123
effectively becomesselect * from bigtable
, which takes forever.Unfortunately it seems the WHERE clause push-down is not happening after 5 iterations of a PL/pgSQL FOR loop.
For instance, say I have a MySQL table:
This is accessible from a Postgres database:
The WHERE clause push-down for plain SQL (not PL/pgSQL) queries work fine. For instance:
I can tell the WHERE clause is passing through by watching /var/log/mysql/mysql.log:
But say I run an equivalent loop in PL/pgSQL:
The /var/log/mysql/mysql.log queries are (in full):
Notice that the WHERE clause disappears after 5 queries.
Searching the web, I found other references to PL/pgSQL slowing down after 5 queries:
https://www.postgresql.org/message-id/CALgmQD9ebXKPgbK5jjbaJ9kCWtOywjjpv-X9+eN0hn5gfGJOjQ@mail.gmail.com
I don't quite understand the replies - something about query plan optimizers - but wrapping the select in an EXECUTE does indeed make it fast again:
If this is a query optimizer problem, can anything be done at the mysql_fdw layer to tell the optimizer to stop messing with it? I've tried
use_remote_estimate 'true'
but it made no difference.Thanks, Jeff
PS: the script to create the MySQL
testdb
database:and to create a linked Postgres
testdb
database: