| Commit message (Collapse) | Author | Age | Files | Lines |
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When inserting new records, only the fields which have been changed
from the defaults will actually be included in the INSERT statement.
The other fields will be populated by the database.
This is more efficient, and also means that it will be safe to
remove database columns without getting subsequent errors in running
app processes (so long as the code in those processes doesn't
contain any references to the removed column).
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If your database supports setting the isolation level for a transaction,
you can set it like so:
Post.transaction(isolation: :serializable) do
# ...
end
Valid isolation levels are:
* `:read_uncommitted`
* `:read_committed`
* `:repeatable_read`
* `:serializable`
You should consult the documentation for your database to understand the
semantics of these different levels:
* http://www.postgresql.org/docs/9.1/static/transaction-iso.html
* https://dev.mysql.com/doc/refman/5.0/en/set-transaction.html
An `ActiveRecord::TransactionIsolationError` will be raised if:
* The adapter does not support setting the isolation level
* You are joining an existing open transaction
* You are creating a nested (savepoint) transaction
The mysql, mysql2 and postgresql adapters support setting the
transaction isolation level. However, support is disabled for mysql
versions below 5, because they are affected by a bug
(http://bugs.mysql.com/bug.php?id=39170) which means the isolation level
gets persisted outside the transaction.
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This method was first seen in 045713ee240fff815edb5962b25d668512649478,
and subsequently reimplemented in
fb2325e35855d62abd2c76ce03feaa3ca7992e4f.
According to @jeremy, this is okay to remove. He thinks it was added
because at the time we didn't have much transaction state to keep track
of, and he viewed it as a hack for us to track it internally, thinking
it was better to ask the connection for the transaction state.
Over the years we have added more and more state to track, a lot of
which is impossible to ask the connection for. So it seems that this is
just a relic of the passed and we will just track the state internally
only.
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The caller needs to have knowledge of the rollback either way, so do it
all in the caller (#transaction)
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This avoids us having to manually increment and decrement it.
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during a"
This reverts commit c24c885209ac2334dc6f798c394a821ee270bec6.
Here's the explanation I just sent to @tenderlove:
Hey,
I've been thinking about about the transaction memory leak thing that we
were discussing.
Example code:
post = nil
Post.transaction do
N.times { post = Post.create }
end
Post.transaction is going to create a real transaction and there will
also be a (savepoint) transaction inside each Post.create.
In an idea world, we'd like all but the last Post instance to be GC'd,
and for the last Post instance to receive its after_commit callback when
Post.transaction returns.
I can't see how this can work using your solution where the Post itself
holds a reference to the transaction it is in; when Post.transaction
returns, control does not switch to any of Post's instance methods, so
it can't trigger the callbacks itself.
What we really want is for the transaction itself to hold weak
references to the objects within the transaction. So those objects can
be GC'd, but if they are not GC'd then the transaction can iterate them
and execute their callbacks.
I've looked into WeakRef implementations that are available. On 1.9.3,
the stdlib weakref library is broken and we shouldn't use it.
There is a better implementation here:
https://github.com/bdurand/ref/blob/master/lib/ref/weak_reference/pure_ruby.rb
We could use that, either by pulling in the gem or just copying the code
in, but it still suffers from the limitation that it uses ObjectSpace
finalizers.
In my testing, this finalizers make GC quite expensive:
https://gist.github.com/3722432
Ruby 2.0 will have a native WeakRef implementation (via
ObjectSpace::WeakMap), hence won't be reliant on finalizers:
http://bugs.ruby-lang.org/issues/4168
So the ultimate solution will be for everyone to use Ruby 2.0, and for
us to just use ObjectSpace::WeakMap.
In the meantime, we have basically 3 options:
The first is to leave it as it is.
The second is to use a finalizer-based weakref implementation and take
the GC perf hit.
The final option is to store object ids rather than the actual objects.
Then use ObjectSpace._id2ref to deference the objects at the end of the
transaction, if they exist. This won't stop memory use growing within
the transaction, but it'll grow more slowly.
I benchmarked the performance of _id2ref this if the object does or does
not exist: https://gist.github.com/3722550
If it does exist it seems decent, but it's hugely more expensive if it
doesn't, probably because we have to do the rescue nil.
Probably most of the time the objects will exist. However the point of
doing this optimisation is to allow people to create a large number of
objects inside a transaction and have them be GC'd. So for that use
case, we'd be replacing one problem with another. I'm not sure which of
the two problems is worse.
My feeling is that we should just leave this for now and come back to it
when Ruby 2.0 is out.
I'm going to revert your commit because I can't see how it solves this.
Hope you don't mind... if I've misunderstood then let me know!
Jon
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transaction.
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Support postgresql partitioning by making INSERT RETURNING optional
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Closes #5202 and #919
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for generating SQL. This improves the code architecture generally, and solves some problems with marshalling. Adapter authors please take note: you now need to define an Adapter.visitor_for method, but it degrades gracefully with a deprecation warning for now.
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normal SQL. fixes #411, #417
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This fixes CVE-2011-0448
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database_statements
otherwise when using external ActiveRecord adapters (e.g. Oracle) database_statements might be loaded before active_support/core_ext/module/deprecation which results in NoMethodError (commit 60cf65def805995bcca184c40b44bb01d86a48aa added "deprecate" call to database_statements.rb)
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