Fix ALTER SEQUENCE locking
In 1753b1b027035029c2a2a1649065762fafbf63f3, the pg_sequence system
catalog was introduced. This made sequence metadata changes
transactional, while the actual sequence values are still behaving
nontransactionally. This requires some refinement in how ALTER
SEQUENCE, which operates on both, locks the sequence and the catalog.
The main problems were:
- Concurrent ALTER SEQUENCE causes "tuple concurrently updated" error,
caused by updates to pg_sequence catalog.
- Sequence WAL writes and catalog updates are not protected by same
lock, which could lead to inconsistent recovery order.
- nextval() disregarding uncommitted ALTER SEQUENCE changes.
To fix, nextval() and friends now lock the sequence using
RowExclusiveLock instead of AccessShareLock. ALTER SEQUENCE locks the
sequence using ShareRowExclusiveLock. This means that nextval() and
ALTER SEQUENCE block each other, and ALTER SEQUENCE on the same sequence
blocks itself. (This was already the case previously for the OWNER TO,
RENAME, and SET SCHEMA variants.) Also, rearrange some code so that the
entire AlterSequence is protected by the lock on the sequence.
As an exception, use reduced locking for ALTER SEQUENCE ... RESTART.
Since that is basically a setval(), it does not require the full locking
of other ALTER SEQUENCE actions. So check whether we are only running a
RESTART and run with less locking if so.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reported-by: Jason Petersen <jason@citusdata.com>
Reported-by: Andres Freund <andres@anarazel.de>
2017-05-10 05:35:31 +02:00
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# Test sequence usage and concurrent sequence DDL
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setup
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{
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CREATE SEQUENCE seq1;
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}
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teardown
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{
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DROP SEQUENCE seq1;
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}
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session "s1"
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setup { BEGIN; }
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step "s1alter" { ALTER SEQUENCE seq1 MAXVALUE 10; }
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step "s1alter2" { ALTER SEQUENCE seq1 MAXVALUE 20; }
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step "s1restart" { ALTER SEQUENCE seq1 RESTART WITH 5; }
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step "s1commit" { COMMIT; }
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session "s2"
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step "s2begin" { BEGIN; }
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step "s2nv" { SELECT nextval('seq1') FROM generate_series(1, 15); }
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step "s2commit" { COMMIT; }
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permutation "s1alter" "s1commit" "s2nv"
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Make ALTER SEQUENCE, including RESTART, fully transactional.
Previously the changes to the "data" part of the sequence, i.e. the
one containing the current value, were not transactional, whereas the
definition, including minimum and maximum value were. That leads to
odd behaviour if a schema change is rolled back, with the potential
that out-of-bound sequence values can be returned.
To avoid the issue create a new relfilenode fork whenever ALTER
SEQUENCE is executed, similar to how TRUNCATE ... RESTART IDENTITY
already is already handled.
This commit also makes ALTER SEQUENCE RESTART transactional, as it
seems to be too confusing to have some forms of ALTER SEQUENCE behave
transactionally, some forms not. This way setval() and nextval() are
not transactional, but DDL is, which seems to make sense.
This commit also rolls back parts of the changes made in 3d092fe540
and f8dc1985f as they're now not needed anymore.
Author: Andres Freund
Discussion: https://postgr.es/m/20170522154227.nvafbsm62sjpbxvd@alap3.anarazel.de
Backpatch: Bug is in master/v10 only
2017-06-01 01:39:27 +02:00
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# Prior to PG10, the s2nv step would see the uncommitted s1alter
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# change, but now it waits.
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Fix ALTER SEQUENCE locking
In 1753b1b027035029c2a2a1649065762fafbf63f3, the pg_sequence system
catalog was introduced. This made sequence metadata changes
transactional, while the actual sequence values are still behaving
nontransactionally. This requires some refinement in how ALTER
SEQUENCE, which operates on both, locks the sequence and the catalog.
The main problems were:
- Concurrent ALTER SEQUENCE causes "tuple concurrently updated" error,
caused by updates to pg_sequence catalog.
- Sequence WAL writes and catalog updates are not protected by same
lock, which could lead to inconsistent recovery order.
- nextval() disregarding uncommitted ALTER SEQUENCE changes.
To fix, nextval() and friends now lock the sequence using
RowExclusiveLock instead of AccessShareLock. ALTER SEQUENCE locks the
sequence using ShareRowExclusiveLock. This means that nextval() and
ALTER SEQUENCE block each other, and ALTER SEQUENCE on the same sequence
blocks itself. (This was already the case previously for the OWNER TO,
RENAME, and SET SCHEMA variants.) Also, rearrange some code so that the
entire AlterSequence is protected by the lock on the sequence.
As an exception, use reduced locking for ALTER SEQUENCE ... RESTART.
Since that is basically a setval(), it does not require the full locking
of other ALTER SEQUENCE actions. So check whether we are only running a
RESTART and run with less locking if so.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reported-by: Jason Petersen <jason@citusdata.com>
Reported-by: Andres Freund <andres@anarazel.de>
2017-05-10 05:35:31 +02:00
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permutation "s1alter" "s2nv" "s1commit"
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2019-08-13 06:53:41 +02:00
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# Prior to PG10, the s2nv step would see the uncommitted s1restart
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Make ALTER SEQUENCE, including RESTART, fully transactional.
Previously the changes to the "data" part of the sequence, i.e. the
one containing the current value, were not transactional, whereas the
definition, including minimum and maximum value were. That leads to
odd behaviour if a schema change is rolled back, with the potential
that out-of-bound sequence values can be returned.
To avoid the issue create a new relfilenode fork whenever ALTER
SEQUENCE is executed, similar to how TRUNCATE ... RESTART IDENTITY
already is already handled.
This commit also makes ALTER SEQUENCE RESTART transactional, as it
seems to be too confusing to have some forms of ALTER SEQUENCE behave
transactionally, some forms not. This way setval() and nextval() are
not transactional, but DDL is, which seems to make sense.
This commit also rolls back parts of the changes made in 3d092fe540
and f8dc1985f as they're now not needed anymore.
Author: Andres Freund
Discussion: https://postgr.es/m/20170522154227.nvafbsm62sjpbxvd@alap3.anarazel.de
Backpatch: Bug is in master/v10 only
2017-06-01 01:39:27 +02:00
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# change, but now it waits.
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permutation "s1restart" "s2nv" "s1commit"
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Fix ALTER SEQUENCE locking
In 1753b1b027035029c2a2a1649065762fafbf63f3, the pg_sequence system
catalog was introduced. This made sequence metadata changes
transactional, while the actual sequence values are still behaving
nontransactionally. This requires some refinement in how ALTER
SEQUENCE, which operates on both, locks the sequence and the catalog.
The main problems were:
- Concurrent ALTER SEQUENCE causes "tuple concurrently updated" error,
caused by updates to pg_sequence catalog.
- Sequence WAL writes and catalog updates are not protected by same
lock, which could lead to inconsistent recovery order.
- nextval() disregarding uncommitted ALTER SEQUENCE changes.
To fix, nextval() and friends now lock the sequence using
RowExclusiveLock instead of AccessShareLock. ALTER SEQUENCE locks the
sequence using ShareRowExclusiveLock. This means that nextval() and
ALTER SEQUENCE block each other, and ALTER SEQUENCE on the same sequence
blocks itself. (This was already the case previously for the OWNER TO,
RENAME, and SET SCHEMA variants.) Also, rearrange some code so that the
entire AlterSequence is protected by the lock on the sequence.
As an exception, use reduced locking for ALTER SEQUENCE ... RESTART.
Since that is basically a setval(), it does not require the full locking
of other ALTER SEQUENCE actions. So check whether we are only running a
RESTART and run with less locking if so.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reported-by: Jason Petersen <jason@citusdata.com>
Reported-by: Andres Freund <andres@anarazel.de>
2017-05-10 05:35:31 +02:00
|
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|
Make ALTER SEQUENCE, including RESTART, fully transactional.
Previously the changes to the "data" part of the sequence, i.e. the
one containing the current value, were not transactional, whereas the
definition, including minimum and maximum value were. That leads to
odd behaviour if a schema change is rolled back, with the potential
that out-of-bound sequence values can be returned.
To avoid the issue create a new relfilenode fork whenever ALTER
SEQUENCE is executed, similar to how TRUNCATE ... RESTART IDENTITY
already is already handled.
This commit also makes ALTER SEQUENCE RESTART transactional, as it
seems to be too confusing to have some forms of ALTER SEQUENCE behave
transactionally, some forms not. This way setval() and nextval() are
not transactional, but DDL is, which seems to make sense.
This commit also rolls back parts of the changes made in 3d092fe540
and f8dc1985f as they're now not needed anymore.
Author: Andres Freund
Discussion: https://postgr.es/m/20170522154227.nvafbsm62sjpbxvd@alap3.anarazel.de
Backpatch: Bug is in master/v10 only
2017-06-01 01:39:27 +02:00
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# In contrast to ALTER setval() is non-transactional, so it doesn't
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# have to wait.
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Fix ALTER SEQUENCE locking
In 1753b1b027035029c2a2a1649065762fafbf63f3, the pg_sequence system
catalog was introduced. This made sequence metadata changes
transactional, while the actual sequence values are still behaving
nontransactionally. This requires some refinement in how ALTER
SEQUENCE, which operates on both, locks the sequence and the catalog.
The main problems were:
- Concurrent ALTER SEQUENCE causes "tuple concurrently updated" error,
caused by updates to pg_sequence catalog.
- Sequence WAL writes and catalog updates are not protected by same
lock, which could lead to inconsistent recovery order.
- nextval() disregarding uncommitted ALTER SEQUENCE changes.
To fix, nextval() and friends now lock the sequence using
RowExclusiveLock instead of AccessShareLock. ALTER SEQUENCE locks the
sequence using ShareRowExclusiveLock. This means that nextval() and
ALTER SEQUENCE block each other, and ALTER SEQUENCE on the same sequence
blocks itself. (This was already the case previously for the OWNER TO,
RENAME, and SET SCHEMA variants.) Also, rearrange some code so that the
entire AlterSequence is protected by the lock on the sequence.
As an exception, use reduced locking for ALTER SEQUENCE ... RESTART.
Since that is basically a setval(), it does not require the full locking
of other ALTER SEQUENCE actions. So check whether we are only running a
RESTART and run with less locking if so.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reported-by: Jason Petersen <jason@citusdata.com>
Reported-by: Andres Freund <andres@anarazel.de>
2017-05-10 05:35:31 +02:00
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permutation "s1restart" "s2nv" "s1commit"
|
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|
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Make ALTER SEQUENCE, including RESTART, fully transactional.
Previously the changes to the "data" part of the sequence, i.e. the
one containing the current value, were not transactional, whereas the
definition, including minimum and maximum value were. That leads to
odd behaviour if a schema change is rolled back, with the potential
that out-of-bound sequence values can be returned.
To avoid the issue create a new relfilenode fork whenever ALTER
SEQUENCE is executed, similar to how TRUNCATE ... RESTART IDENTITY
already is already handled.
This commit also makes ALTER SEQUENCE RESTART transactional, as it
seems to be too confusing to have some forms of ALTER SEQUENCE behave
transactionally, some forms not. This way setval() and nextval() are
not transactional, but DDL is, which seems to make sense.
This commit also rolls back parts of the changes made in 3d092fe540
and f8dc1985f as they're now not needed anymore.
Author: Andres Freund
Discussion: https://postgr.es/m/20170522154227.nvafbsm62sjpbxvd@alap3.anarazel.de
Backpatch: Bug is in master/v10 only
2017-06-01 01:39:27 +02:00
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# nextval doesn't release lock until transaction end, so s1alter2 has
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# to wait for s2commit.
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permutation "s2begin" "s2nv" "s1alter2" "s2commit" "s1commit"
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