Support PostgreSQL 10 whose sequences do not know increment_by

[yahonda]

Summary

Addresses #28780

• Each sequence does not know increment_by or min_value since
  PostgreSQL 10. A new system catalog pg_sequences knows both. postgres/postgres@1753b1b

• Since pg_sequences does not exist PostgreSQL 9.6 or earlier version
  This commit addresses by removing increment_by or min_value

• setval 3rd argument needs to set to false only when the table has
  no rows to avoid nextval(<sequence_name>) returns 2 where 1 is
  expected.

• Replaced min_value with 1 since it is necessary only when
  the table has no rows. If someone wants to reset sequence to non 1 when table has no rows new pull requests/commits required.

[rails-bot]

r? @rafaelfranca

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[pixeltrix]

@yahonda will next_val automatically return min_value if you setval to 1?

[yahonda]

No. The value set at setval must be equal or higher than the min_value. It shows this error:
ERROR: setval: value 1 is out of bounds for sequence "test_seq_min_value_100" (100..9223372036854775807)

• PostgreSQL version

postgres=# create database test;
CREATE DATABASE
postgres=# \q
$ psql -d test
psql (10devel)
Type "help" for help.

• create a sequence with minvalue 100

CREATE SEQUENCE
test=# select nextval('test_seq_min_value_100');
 nextval
---------
     100
(1 row)

test=# select nextval('test_seq_min_value_100');
 nextval
---------
     101
(1 row)

test=# select nextval('test_seq_min_value_100');
 nextval
---------
     102
(1 row)

test=# select nextval('test_seq_min_value_100');
 nextval
---------
     103
(1 row)

test=# select nextval('test_seq_min_value_100');
 nextval
---------
     104
(1 row)

test=# select nextval('test_seq_min_value_100');
 nextval
---------
     105
(1 row)

test=# select setval('test_seq_min_value_100', 1, true);
ERROR:  setval: value 1 is out of bounds for sequence "test_seq_min_value_100" (100..9223372036854775807)
test=# select setval('test_seq_min_value_100', 1, false);
ERROR:  setval: value 1 is out of bounds for sequence "test_seq_min_value_100" (100..9223372036854775807)

[pixeltrix]

Dang - I think we need to address somehow in this PR

[yahonda]

To get the min_value we will need to retrieve it from pg_sequences starting from PostgreSQL 10.

This pull request now aims to create the same statement available for whichever PostgreSQL version.
But we may need to consider to implement if postgresql_version >= 100000 kind of approach.

activerecord_unittest=# \x
Expanded display is on.
activerecord_unittest=# select * FROM "public"."topics_id_seq";
-[ RECORD 1 ]---
last_value | 100
log_cnt    | 0
is_called  | t

activerecord_unittest=# select * from pg_sequences where schemaname = 'public' and sequencename = 'topics_id_seq';
-[ RECORD 1 ]-+--------------------
schemaname    | public
sequencename  | topics_id_seq
sequenceowner | yahonda
data_type     | bigint
start_value   | 1
min_value     | 1
max_value     | 9223372036854775807
increment_by  | 1
cycle         | f
cache_size    | 1
last_value    | 100

activerecord_unittest=#

[yahonda]

Let me update this pull request using if postgresql_version >= 100000 approach.

[pixeltrix]

Is there any discussions on this topic in the PostgreSQL community - seems like a very abrupt change for users to deal with.

[yahonda]

Here is the link to pgsql-hackers mailing list discussion for this change.

https://www.postgresql.org/message-id/flat/7842a868-0df8-6087-2332-59ba0d6a2210%402ndquadrant.com#7842a868-0df8-6087-2332-59ba0d6a2210@2ndquadrant.com

and commit.

postgres/postgres@1753b1b

[rafaelfranca]

@pixeltrix assigning to you since you already got the initial context

[pixeltrix]

@yahonda is there a way of use ALTER SEQUENCE to do what we want?

[yahonda]

alter sequence statement also requires start value is equal or higher than minvalue.

• Error message

test=#
test=# alter sequence test_seq_for_alter_sequence_min_value_100 start 1;
ERROR:  START value (1) cannot be less than MINVALUE (100)
test=#

• Test output

test=# create sequence test_seq_for_alter_sequence_min_value_100 minvalue 100;
CREATE SEQUENCE
test=# \x
Expanded display is on.
test=# select * from test_seq_for_alter_sequence_min_value_100;
-[ RECORD 1 ]---
last_value | 100
log_cnt    | 0
is_called  | f

test=# select * from pg_sequences where sequencename = 'test_seq_for_alter_sequence_min_value_100';
-[ RECORD 1 ]-+------------------------------------------
schemaname    | public
sequencename  | test_seq_for_alter_sequence_min_value_100
sequenceowner | yahonda
data_type     | bigint
start_value   | 100
min_value     | 100
max_value     | 9223372036854775807
increment_by  | 1
cycle         | f
cache_size    | 1
last_value    |

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 100

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 101

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 102

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 103

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 104

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 105

test=#
test=# alter sequence test_seq_for_alter_sequence_min_value_100 start 1;
ERROR:  START value (1) cannot be less than MINVALUE (100)
test=#

[pixeltrix]

@yahonda there's a RESTART option that can either be blank or WITH <value>

[yahonda]

Yeah, there is an interesting option. But actually restart is same as setting is_called to false at setval.

https://www.postgresql.org/docs/9.6/static/sql-altersequence.html

This is equivalent to calling the setval function with is_called = false:

test=# alter sequence test_seq_for_alter_sequence_min_value_100 restart 1;
ERROR:  RESTART value (1) cannot be less than MINVALUE (100)

What we can do is setting minvalue = 1 to override the current minvalue as follows.
There will be no differences from the current pull request implementation since it sets setval 2nd argument as 1 when the table is empty.

test=# alter sequence test_seq_for_alter_sequence_min_value_100 minvalue 1 restart 1;
ALTER SEQUENCE
test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 1

test=#

• Test

test=# \q
[yahonda@li366-176 ~]$ psql -d test
psql (10devel)
Type "help" for help.

test=# create sequence test_seq_for_alter_sequence_min_value_100 minvalue 100;
CREATE SEQUENCE
test=# \x
Expanded display is on.
test=# select * from test_seq_for_alter_sequence_min_value_100;
-[ RECORD 1 ]---
last_value | 100
log_cnt    | 0
is_called  | f

test=# select * from pg_sequences where sequencename = 'test_seq_for_alter_sequence_min_value_100';
-[ RECORD 1 ]-+------------------------------------------
schemaname    | public
sequencename  | test_seq_for_alter_sequence_min_value_100
sequenceowner | yahonda
data_type     | bigint
start_value   | 100
min_value     | 100
max_value     | 9223372036854775807
increment_by  | 1
cycle         | f
cache_size    | 1
last_value    |

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 100

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 101

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 102

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 103

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 104

test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 105

test=# alter sequence test_seq_for_alter_sequence_min_value_100 restart 1;
ERROR:  RESTART value (1) cannot be less than MINVALUE (100)
test=# alter sequence test_seq_for_alter_sequence_min_value_100 minvalue 1 restart 1;
ALTER SEQUENCE
test=# select nextval('test_seq_for_alter_sequence_min_value_100');
-[ RECORD 1 ]
nextval | 1

test=#

[pixeltrix]

I guess we have to go with a if postgresql_version >= 100000 approach then 😞

I suspect this will be the first of many such conditionals.

[yahonda]

Agreed. Let me update the commit to handle if postgresql_version >= 100000.

[yahonda]

Closing this pull request. Opened another pull request #28864 which handles min_value correctly.