| Commit message (Collapse) | Author | Age | Files | Lines |
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Currently 1,000 transactions creates 10,000 objects regardless whether
it is necessary or not.
This makes allocation on demand in transactions, now 1,000 transactions
creates required 5,000 objects only by default.
```ruby
ObjectSpace::AllocationTracer.setup(%i{path line type})
pp ObjectSpace::AllocationTracer.trace {
1_000.times { User.create }
}.select { |k, _| k[0].end_with?("transaction.rb") }
```
Before (95d038f):
```
{["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
209,
:T_HASH]=>[1000, 0, 715, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
210,
:T_OBJECT]=>[1000, 0, 715, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
210,
:T_HASH]=>[1000, 0, 715, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
80,
:T_OBJECT]=>[1000, 0, 715, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
8,
:T_ARRAY]=>[1000, 0, 715, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
81,
:T_ARRAY]=>[1000, 0, 715, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
289,
:T_STRING]=>[1000, 0, 714, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
116,
:T_ARRAY]=>[1000, 0, 714, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
120,
:T_ARRAY]=>[1000, 0, 714, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
121,
:T_HASH]=>[1000, 0, 714, 0, 1, 0]}
```
After (this change):
```
{["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
213,
:T_HASH]=>[1000, 0, 739, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
214,
:T_OBJECT]=>[1000, 0, 739, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
214,
:T_HASH]=>[1000, 0, 739, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
81,
:T_OBJECT]=>[1000, 0, 739, 0, 1, 0],
["~/rails/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb",
304,
:T_STRING]=>[1000, 0, 738, 0, 1, 0]}
```
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We sometimes say "✂️ newline after `private`" in a code review (e.g.
https://github.com/rails/rails/pull/18546#discussion_r23188776,
https://github.com/rails/rails/pull/34832#discussion_r244847195).
Now `Layout/EmptyLinesAroundAccessModifier` cop have new enforced style
`EnforcedStyle: only_before` (https://github.com/rubocop-hq/rubocop/pull/7059).
That cop and enforced style will reduce the our code review cost.
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transaction
Currently, `committed!`/`rolledback!` will only be attempted for the
first enrolled record in the transaction, that will cause some
problematic behaviors.
The first one problem, `clear_transaction_record_state` won't be called
even if the transaction is finalized except the first enrolled record.
This means that de-duplicated records in the transaction won't refer
latest state (e.g. won't happen rolling back record state).
The second one problem, the enrolled order is not always the same as the
order in which the actions actually happened, the first enrolled record
may succeed no actions (e.g. `destroy` has already succeeded on another
record during `before_destroy`), it will lose to fire any transactional
callbacks.
To avoid both problems, we should attempt `committed!`/`rolledback!` to
all enrolled records in the transaction.
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The transaction used to restore fixtures is an implementation detail
that should be abstracted away. Idealy a test should behave the same
wether or not transactional fixtures are enabled.
However since transactions have been made lazy, the fixture
transaction started leaking into tests case. e.g. consider the
following (oversimplified) test:
```ruby
class SQLSubscriber
attr_accessor :sql
def initialize
@sql = []
end
def call(*, event)
sql << event[:sql]
end
end
subscriber = SQLSubscriber.new
ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
User.connection.execute('SELECT 1', 'Generic name')
assert_equal ['SELECT 1'], subscriber.sql
```
On Rails 6 it starts to break because the `sql` array will be `['BEGIN', 'SELECT 1']`.
Several things are wrong here:
- That transaction is not generated by the tested code, so it shouldn't be visible.
- The transaction is not even closed yet, which again doesn't reflect the reality.
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Currently we sometimes find a redundant begin block in code review
(e.g. https://github.com/rails/rails/pull/33604#discussion_r209784205).
I'd like to enable `Style/RedundantBegin` cop to avoid that, since
rescue/else/ensure are allowed inside do/end blocks in Ruby 2.5
(https://bugs.ruby-lang.org/issues/12906), so we'd probably meets with
that situation than before.
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When a record with transactional callbacks is saved, it's attached to
the current transaction so that the callbacks can be run when the
transaction is committed. Records can also be added manually with
`add_transaction_record`, even if they have no transactional callbacks.
When a nested transaction is committed, its records are transferred to
the parent transaction, as transactional callbacks should only be run
when the outermost transaction is committed (the "real" transaction).
However, this currently only happens when the record has transactional
callbacks, and not when added manually with `add_transaction_record`.
If a record is added to a nested transaction, we should always attach it
to the parent transaction when the nested transaction is committed,
regardless of whether it has any transactional callbacks.
[Eugene Kenny & Ryuta Kamizono]
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If a transaction is opened and closed without any queries being run, we
can safely omit the `BEGIN` and `COMMIT` statements, as they only exist
to modify the connection's behaviour inside the transaction. This
removes the overhead of those statements when saving a record with no
changes, which makes workarounds like `save if changed?` unnecessary.
This implementation buffers transactions inside the transaction manager
and materializes them the next time the connection is used. For this to
work, the adapter needs to guard all connection use with a call to
`materialize_transactions`. Because of this, adapters must opt in to get
this new behaviour by implementing `supports_lazy_transactions?`.
If `raw_connection` is used to get a reference to the underlying
database connection, the behaviour is disabled and transactions are
opened eagerly, as we can't know how the connection will be used.
However when the connection is checked back into the pool, we can assume
that the application won't use the reference again and reenable lazy
transactions. This prevents a single `raw_connection` call from
disabling lazy transactions for the lifetime of the connection.
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After a real (non-savepoint) transaction has committed or rolled back,
the original persistence-related state for all records modified in that
transaction is discarded or restored, respectively.
When the model has transactional callbacks, this happens synchronously
in the `committed!` or `rolled_back!` methods; otherwise, it happens
lazily the next time the record's persistence-related state is accessed.
The synchronous code path always finalizes the state of the record, but
the lazy code path only pops one "level" from the transaction counter,
assuming it will always reach zero immediately after a real transaction.
As the test cases included here demonstrate, that isn't always the case.
By using the same logic as the synchronous code path, we ensure that the
record's state is always updated after a real transaction has finished.
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This was added in 280587588aba6ce13717cd6679e3f2b43d287443, but has been
unused since 392eeecc11a291e406db927a18b75f41b2658253.
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```
[NoMethodError]: undefined method `state' for nil:NilClass Method:[rescue in block in refresh]
```
In `within_new_transaction`, there is the possibility that
`begin_transaction` returns a `nil`. (i.e.: so `transaction = nil`)
So this method is checking `transaction` for nil in 2 spots.
Unfortunately, there is one line that is not checking `transaction` for `nil`
That line, `commit_transaction`, throws an exception for us in AR 5.0.0.1
The problem with the method is finally realized in the error checking itself.
it calls `transaction.state` (i.e.: nil.state) and that is the final exception
raised.
The actual underlying (user) issue is hidden by this line.
Solution is test transaction for nil.
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Because the deprecation message is not yet released.
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Let's say you have a nested transaction and both records are saved.
Before the outer transaction closes, a rollback is performed. Previously
the record in the outer transaction would get marked as not persisted
but the inner transaction would get persisted.
```ruby
Post.transaction do
post_one.save # will get rolled back
Post.transaction(requires_new: true) do
post_two.save # incorrectly remains marked as persisted
end
raise ActiveRecord::Rollback
end
```
To fix this the PR changes transaction handling to have the child
transaction ask the parent how the records should be marked. When
there are child transactions, it will always be a SavpointTransaction
because the stack isn't empty. From there we pass the parent_transaction
to the child SavepointTransaction where we add the children to the parent
so the parent can mark the inner transaction as rolledback and thus mark
the record as not persisted.
`update_attributes_from_transaction_state` uses the `completed?` check to
correctly mark all the transactions as rolledback and the inner record as
not persisted.
```ruby
Post.transaction do
post_one.save # will get rolled back
Post.transaction(requires_new: true) do
post_two.save # with new behavior, correctly marked as not persisted
on rollback
end
raise ActiveRecord::Rollback
end
```
Fixes #29320
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`set_state` was directly setting the transaction state instance
variable. It's better to set the state via specific methods (`rollback!`
and `commit!` respectively.
While undocumented and untested, it's possible someone is using
`set_state` in their app or gem so I've added a deprecation notice to
it.
No where in the app do we use `nullify!` but I wanted to keep existing
behavior while replacing the method with a better pattern.
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This reverts commit 3420a14590c0e6915d8b6c242887f74adb4120f9, reversing
changes made to afb66a5a598ce4ac74ad84b125a5abf046dcf5aa.
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Transactional-fixture using tests with racing threads and inter-thread
synchronisation inside transaction blocks will now deadlock... but
without this, they would just crash.
In 5.0, the threads didn't share a connection at all, so it would've
worked... but with the main thread inside the fixture transaction, they
wouldn't've been able to see each other.
So: as far as I can tell, the set of operations this "breaks" never had
a compelling use case. Meanwhile, it provides an increased level of
coherency to the operational feel of transactional fixtures.
If this does cause anyone problems, they're probably best off disabling
transactional fixtures on the affected tests, and managing transactions
themselves.
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The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.
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samphilipd/sam/properly_deallocate_prepared_statements_outside_of_transaction
Correctly deallocate prepared statements if we fail inside a transaction
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- Addresses issue #12330
Overview
========
Cached postgres prepared statements become invalidated if the schema
changes in a way that it affects the returned result.
Examples:
- adding or removing a column then doing a 'SELECT *'
- removing the foo column then doing a 'SELECT bar.foo'
In normal operation this isn't a problem, we can rescue the error,
deallocate the prepared statement and re-issue the command.
However in PostgreSQL transactions, once any command fails, the
transaction becomes 'poisoned' and any subsequent commands will raise
InFailedSQLTransaction.
This includes DEALLOCATE statements, so the default deallocation
strategy instead of removing the cached prepared statement instead
raises InFailedSQLTransaction.
Why this is bad
===============
1. InFailedSQLTransaction is a fairly cryptic error and doesn't
communicate any useful information about what has actually gone wrong.
2. In the naive implementation the prepared statement never gets
deallocated - it stays alive for the length of the session taking up
memory on the postgres server.
3. It is unsafe to retry the transaction because the bad prepared
statement is still in the cache and we would see the exact same failure
repeated.
Solution
========
If we are outside a transaction we can continue to handle these failures
gracefully in the usual way.
Inside a transaction instead of issuing a DEALLOCATE command that will
certainly fail, we now raise
ActiveRecord::PreparedStatementCacheExpired.
This can be handled further up the stack, notably inside
TransactionManager#within_new_transaction. Here we can make sure to
first rollback the transaction, then safely issue DEALLOCATE statements
to invalidate the rest of the cached prepared statements.
This also allows the user (or some gem) the opportunity to catch this error and
voluntarily retry the transaction if a schema change causes the prepared
statement cache to become invalidated.
Because the outdated statement has been deallocated, we can expect the
transaction to succeed on the second try.
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When a `before_commit` callback raises, the database is rolled back but
AR's record of the current transaction is not, leaving the connection in
a perpetually broken state that affects all future users of the
connection: subsequent requests, jobs, etc. They'll think a transaction
is active when none is, so they won't BEGIN on their own. This manifests
as missing `after_commit` callbacks and broken ROLLBACKs.
This happens because `before_commit` callbacks fire before the current
transaction is popped from the stack, but the exception-handling path
they hit assumes that the current transaction was already popped. So the
database ROLLBACK is issued, but the transaction stack is left intact.
Common cause: deadlocked `#touch`, which is now implemented with
`before_commit` callbacks.
What's next:
* We shouldn't allow active transaction state when checking in or out
from the connection pool. Verify that conns are clean.
* Closer review of txn manager sad paths. Are we missing other spots
where we'd end up with incorrect txn state? What's the worst that can
happen if txn state drifts? How can we guarantee it doesn't and
contain the fallout if it does?
Thanks for @tomafro for expert diagnosis!
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Fixes https://github.com/rails/rails/issues/22819
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This reverts commit 393e65b4170608593ad82377a9eadc918e85698d and
ec51c3fedd16b561d096dcc1a6705fdc02ab7666
We don't want the records to hold hard references to transactions
because they point at records that have callbacks.
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this lets us keep singleton instances of "state" values and precalculate
return values of things like `finalized?` and `completed?`.
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this way we don't have to mutate a state object, we can just change the
state of the txn
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As far as I can tell nobody is setting this variable.
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[fixes #18903]
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the transaction object shouldn't know so much about active record
objects, so let's push the conditionals in to the instance.
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after_commit callbacks run after committing a transaction whose parent
is not `joinable?`: un-nested transactions, transactions within test
cases, and transactions in `console --sandbox`.
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It is up to the TransactionManager keep the state of current transaction, so after it commits it needs to copy any remaning record to the next current transaction
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As discussed before, those methods should receive a keyword args instead of just parameters
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Before this change any error raised inside a transaction callback
are rescued and printed in the logs.
Now these errors are not rescue anymore and just bubble up,
as the other callbacks.
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Data corruption risk: Roll back open transactions when the running thread is killed.
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Currently, Active Record will rescue any errors raised within
after_rollback/after_create callbacks and print them to the
logs. Next versions of rails will not rescue those errors anymore,
and just bubble them up, as the other callbacks.
This adds a opt-in flag to enable that behaviour, of not rescuing
the errors.
Example:
# For not swallow errors in after_commit/after_rollback
config.active_record.errors_in_transactional_callbacks = true
[fixes #13460]
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after_commit should not run in nested transactions, however they should
run once the outermost transaction gets committed. This patch fixes the
problem copying the records from the Savepoint to its parent. So the
RealTransaction will have all records that needs to run callbacks on it.
[fixes #16425]
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Use `commit_transaction`/`rollback_transaction` on
`within_new_transaction` method, so they make sure they `pop` the
transaction from the stack before calling the methods `commit`/`rollback`.
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Transaction class doesnt need to encapsulate the transaction state using
inheritance.
This removes all Transaction subclasses, and let the Transaction object
controls different actions based on its own state. Basically the only
actions would behave differently are `being`,`commit`,`rollback` as they
could act in a savepoint or in a real transaction.
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