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<title>Berkeley DB: env txn</title>
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<h1><i>env</i> <b>txn</b></h1>
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<p>The <i>env</i> <b>txn</b> command begins a transaction. The returned transaction
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handle is bound to a Tcl command of the form <b>env.txnX</b>, where
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X is an integer starting at 0 (for example, env0.txn0 and env0.txn1).
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It is through this Tcl command that the script accesses the transaction
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<p>The options are as follows:
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<p><dt>-nosync<dd>Do not synchronously flush the log when this transaction commits or
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prepares. This means the transaction will exhibit the ACI (atomicity,
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consistency, and isolation) properties, but not D (durability); that
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is, database integrity will be maintained, but it is possible that this
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transaction may be undone during recovery instead of being redone.
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<p>This behavior may be set for an entire Berkeley DB environment as part of
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the <b>berkdb env</b> interface.
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<p><dt>-nowait<dd>If a lock is unavailable for any Berkeley DB operation performed in the context
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of this transaction, throw a Tcl error immediately instead of blocking on
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<p><dt>-parent txnid<dd>Create the new transaction as a nested transaction, with the specified
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transaction indicated as its parent. Transactions may be nested to any
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<p><dt>-sync<dd>Synchronously flush the log when this transaction commits or prepares.
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This means the transaction will exhibit all of the ACID (atomicity,
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consistency, isolation, and durability) properties.
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<p>This behavior is the default for Berkeley DB environments unless the
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<b>-nosync</b> option was specified to the <b>berkdb env</b> interface.
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<p>The <i>env</i> <b>txn</b> command returns a transaction handle on success.
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<p>In the case of error, a Tcl error is thrown.
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