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DOCSP-25487 update transaction docs (#5448)
* General version and term cleanup * More deprecated version info cleanup, clarified collection creation is implicit if none exists * Fixed line break * Cleaned up Transactions and Operations topic * Lingering mention of collection reqs * Indentation fixes * Fixed indentation * Internal PR feedback * Externalized common content to includes * Internal review feedback * Typo fix
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source/core/transactions-operations.txt

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@@ -18,12 +18,6 @@ For transactions:
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.. include:: /includes/extracts/transactions-operations-crud.rst
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Operations that affect the database catalog, such as creating or
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dropping a collection or an index, are not allowed in multi-document
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transactions. For example, a multi-document transaction cannot include
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an insert operation that would result in the creation of a new
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collection. See :ref:`transactions-operations-ref-restricted`.
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Operations Supported in Multi-Document Transactions
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---------------------------------------------------
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@@ -38,11 +32,11 @@ The following read/write operations are allowed in transactions:
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.. note:: Updates to Shard Key Values
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Starting in MongoDB 4.2, you can update a document's shard key value
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(unless the shard key field is the immutable ``_id`` field) by
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issuing single-document update/findAndModify
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operations either in a transaction or as a :doc:`retryable write
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</core/retryable-writes>`. For details, see :ref:`update-shard-key`.
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You can update a document's shard key value (unless the shard key
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field is the immutable ``_id`` field) by issuing single-document
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update / findAndModify operations either in a transaction or as a
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:doc:`retryable write </core/retryable-writes>`. For details, see
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:ref:`update-shard-key`.
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.. _transactions-operations-count:
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Administration Operations
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~~~~~~~~~~~~~~~~~~~~~~~~~
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Starting in MongoDB 4.4 with :ref:`feature compatibility version (fcv)
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<view-fcv>` ``"4.4"``, you can create collections and indexes inside a
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:ref:`multi-document transaction <transactions>` if the
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transaction is :red:`not` a cross-shard write transaction.
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.. include:: /includes/transactions/create-collections-indexes-in-transaction.rst
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.. _transactions-operations-ddl-explicit:
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source/core/transactions.txt

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:class: twocols
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.. meta::
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:description: For situations that require atomicity of reads and writes to multiple documents (in a single or multiple collections), MongoDB supports multi-document transactions.
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:description: For situations that require atomicity of reads and writes to multiple documents (in a single or multiple collections), MongoDB supports multi-document transactions, also called distributed transactions.
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:keywords: MongoDB, transactions, distributed transactions, MongoDB multi-document transactions, MongoDB multi-statement transactions, java transaction examples, python transaction examples, node transaction examples, php transaction examples, scala transaction examples, csharp transaction examples, perl transaction examples, ruby transaction examples
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In MongoDB, an operation on a single document is atomic. Because you can
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use embedded documents and arrays to capture relationships between data
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in a single document structure instead of normalizing across multiple
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documents and collections, this single-document atomicity obviates the
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need for multi-document transactions for many practical use cases.
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need for distributed transactions for many practical use cases.
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For situations that require atomicity of reads and writes to multiple
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documents (in a single or multiple collections), MongoDB supports
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multi-document transactions. With distributed transactions,
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distributed transactions. With distributed transactions,
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transactions can be used across multiple operations, collections,
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databases, documents, and shards.
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Transactions and Atomicity
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--------------------------
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.. note:: Distributed Transactions and Multi-Document Transactions
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.. include:: /includes/transactions/distributed-transaction-repl-shard-support.rst
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Starting in MongoDB 4.2, the two terms are synonymous. Distributed
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transactions refer to multi-document transactions on sharded
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clusters and replica sets. Multi-document transactions (whether on
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sharded clusters or replica sets) are also known as distributed
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transactions starting in MongoDB 4.2.
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For situations that require atomicity of reads and writes to multiple
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documents (in a single or multiple collections), MongoDB supports
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multi-document transactions:
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- **In version 4.0**, MongoDB supports multi-document transactions on
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replica sets.
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- **In version 4.2**, MongoDB introduces distributed transactions,
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which adds support for multi-document transactions on sharded
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clusters and incorporates the existing support for
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multi-document transactions on replica sets.
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To use transactions on MongoDB 4.2 deployments (replica sets and
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sharded clusters), clients :red:`must` use MongoDB drivers updated for
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MongoDB 4.2.
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Multi-document transactions are atomic (i.e. provide an
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"all-or-nothing" proposition):
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Distributed transactions are atomic. They provide an "all-or-nothing"
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proposition:
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- When a transaction commits, all data changes made in the transaction
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are saved and visible outside the transaction. That is, a transaction
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---------------------------
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Distributed transactions can be used across multiple operations,
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collections, databases, documents, and, starting in MongoDB 4.2, shards.
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collections, databases, documents, and shards.
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For transactions:
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Create Collections and Indexes In a Transaction
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Starting in MongoDB 4.4, you can perform the following operations inside
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of a :ref:`multi-document transaction <transactions>` as long as
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the transaction is not a cross-shard write transaction:
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You can perform the following operations inside of a :ref:`distributed
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transaction <transactions>` as long as the transaction is not a
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cross-shard write transaction:
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- Create collections.
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- Create indexes on new empty collections created earlier in the same
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transaction.
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In MongoDB 4.2 and earlier, operations that affect the database catalog,
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such as creating or dropping a collection or an index, are
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:red:`disallowed` in transactions.
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When creating a collection inside a transaction:
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- You can :ref:`implicitly create a collection
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Transactions and Sessions
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-------------------------
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- Transactions are associated with a session; i.e. you start a
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transaction for a session.
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- Transactions are associated with a session
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- At any given time, you can have at most one open transaction for a
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session.
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``"majority"``
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``````````````
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- Read concern :readconcern:`"majority"` returns data that has been
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acknowledged by a majority of the replica set members (i.e. data
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cannot be rolled back) **if** the transaction commits with
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:ref:`write concern "majority" <transactions-write-concern>`.
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- If the transaction does not use :ref:`write concern "majority"
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<transactions-write-concern>` for the commit, the
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:readconcern:`"majority"` read concern provides **no** guarantees that
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read operations read majority-committed data.
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- If the transaction commits with :ref:`write concern "majority"
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<transactions-write-concern>`, read concern :readconcern:`"majority"`
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returns data that has been acknowledged by a majority of the replica
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set members and can't be rolled back. Otherwise, read concern
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:readconcern:`"majority"` provides no guarantees that read operations
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read majority-committed data.
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- For transactions on sharded cluster, :readconcern:`"majority"` read
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concern cannot guarantee that the data is from the same snapshot
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view across the shards. If snapshot isolation is required, use
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:ref:`transactions-read-concern-snapshot` read concern.
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- For transactions on sharded cluster, read concern
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:readconcern:`"majority"` can't guarantee that the data is from the
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same snapshot view across the shards. If snapshot isolation is
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required, use read concern :ref:`transactions-read-concern-snapshot`.
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.. _transactions-read-concern-snapshot:
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<replica-set-arbiter-configuration>`. See
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:ref:`wc-default-behavior`.
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- :writeconcern:`w: 1 <\<number\>>` in MongoDB 4.4 and earlier.
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- :writeconcern:`w: 1 <\<number\>>`
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.. seealso::
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- Write concern :writeconcern:`w: "majority" <"majority">` returns
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acknowledgement after the commit has been applied to a majority
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(M) of voting members; i.e. the commit has been applied to the
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(M) of voting members, meaning the commit has been applied to the
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primary and (M-1) voting secondaries.
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- When you commit with :writeconcern:`w: "majority" <"majority">`
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* - :binary:`~bin.mongod` and :binary:`~bin.mongos` log messages
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- Includes information on slow transactions (i.e. transactions
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- Includes information on slow transactions, which are transactions
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that exceed the :setting:`operationProfiling.slowOpThresholdMs`
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threshold) under the :data:`TXN` log component.
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