MongoDB::ClientSession - MongoDB session and transaction management
version v2.2.2
my $session = $client->start_session( $options );
# use session in operations
my $result = $collection->find( { id => 1 }, { session => $session } );
# use sessions for transactions
$session->start_transaction;
...
if ( $ok ) {
$session->commit_transaction;
}
else {
$session->abort_transaction;
}
This class encapsulates an active session for use with the current client.
Sessions support is new with MongoDB 3.6, and can be used in replica set and
sharded MongoDB clusters.
If you specifically apply a session to an operation, then the operation will be
performed with that session id. If you do not provide a session for an
operation, and the server supports sessions, then an implicit session will be
created and used for this operation.
The only exception to this is for unacknowledged writes - the driver will not
provide an implicit session for this, and if you provide a session then the
driver will raise an error.
During cursors, if a session is not provided then an implicit session will be
created which is then used for the lifetime of the cursor. If you provide a
session, then note that ending the session and then continuing to use the
cursor will raise an error.
NOTE: Per threads documentation, use of Perl threads is discouraged by the
maintainers of Perl and the MongoDB Perl driver does not test or provide support
for use with threads.
Sessions are NOT thread safe, and should only be used by one thread at a time.
Using a session across multiple threads is unsupported and unexpected issues
and errors may occur. Note that the driver does not check for multi-threaded
use.
A session may be associated with at most one open transaction (on MongoDB
4.0+). For detailed instructions on how to use transactions with drivers,
see the MongoDB manual page:
Transactions.
The client this session was created using. Sessions may only be used
with the client that created them.
Stores the last received $clusterTime for the client session. This is an
opaque value, to set it use the the advance_cluster_time manpage function.
Options provided for this particular session. Available options include:
-
causalConsistency - If true, will enable causalConsistency for this session. For more information, see MongoDB documentation on Causal Consistency. Note that causalConsistency does not apply for unacknowledged writes. Defaults to true.
-
defaultTransactionOptions - Options to use by default for transactions created with this session. If when creating a transaction, none or only some of the transaction options are defined, these options will be used as a fallback. Defaults to inheriting from the parent client. See start_transaction for available options.
The last operation time. This is updated when an operation is performed during
this session, or when advance_operation_time is called. Used for causal
consistency.
The session id for this particular session. This should be considered
an opaque value. If end_session has been called, this returns undef.
my $cluster_time = $session->get_latest_cluster_time;
Returns the latest cluster time, when compared with this session's recorded
cluster time and the main client cluster time. If neither is defined, returns
undef.
$session->advance_cluster_time( $cluster_time );
Update the $clusterTime for this session. Stores the value in
cluster_time. If the cluster time provided is more recent than the sessions
current cluster time, then the session will be updated to this provided value.
Setting the $clusterTime with a manually crafted value may cause a server
error. It is recommended to only use $clusterTime values retrieved from
database calls.
$session->advance_operation_time( $operation_time );
Update the operation_time for this session. If the value provided is more
recent than the sessions current operation time, then the session will be
updated to this provided value.
Setting operation_time with a manually crafted value may cause a server
error. It is recommended to only use an operation_time retrieved from
another session or directly from a database call.
$session->start_transaction;
$session->start_transaction( $options );
Start a transaction in this session. If a transaction is already in
progress or if the driver can detect that the client is connected to a
topology that does not support transactions, this method will throw an
error.
A hash reference of options may be provided. Valid keys include:
-
readConcern - The read concern to use for the first command in this transaction. If not defined here or in the defaultTransactionOptions in options, will inherit from the parent client.
-
writeConcern - The write concern to use for committing or aborting this transaction. As per readConcern, if not defined here then the value defined in defaultTransactionOptions will be used, or the parent client if not defined.
-
readPreference - The read preference to use for all read operations in this transaction. If not defined, then will inherit from defaultTransactionOptions or from the parent client. This value will override all other read preferences set in any subsequent commands inside this transaction.
-
maxCommitTimeMS - The maxCommitTimeMS specifies a cumulative time limit in milliseconds for processing operations on the cursor. MongoDB interrupts the operation at the earliest following interrupt point.
$session->commit_transaction;
Commit the current transaction. This will use the writeConcern set on this
transaction.
If called when no transaction is in progress, then this method will throw
an error.
If the commit operation encounters an error, an error is thrown. If the
error is a transient commit error, the error object will have a label
containing ``UnknownTransactionCommitResult'' as an element and the commit
operation can be retried. This can be checked via the has_error_label:
LOOP: {
eval {
$session->commit_transaction;
};
if ( my $error = $@ ) {
if ( $error->has_error_label("UnknownTransactionCommitResult") ) {
redo LOOP;
}
else {
die $error;
}
}
}
$session->abort_transaction;
Aborts the current transaction. If no transaction is in progress, then this
method will throw an error. Otherwise, this method will suppress all other
errors (including network and database errors).
$session->end_session;
Close this particular session and release the session ID for reuse or
recycling. If a transaction is in progress, it will be aborted. Has no
effect after calling for the first time.
This will be called automatically by the object destructor.
$session->with_transaction($callback, $options);
Execute a callback in a transaction.
This method starts a transaction on this session, executes $callback, and
then commits the transaction, returning the return value of the $callback.
The $callback will be executed at least once.
If the $callback throws an error, the transaction will be aborted. If less
than 120 seconds have passed since calling with_transaction, and the error
has a TransientTransactionError label, the transaction will be restarted and
the callback will be executed again. Otherwise, the error will be thrown.
If the $callback succeeds, then the transaction will be committed. If an
error is thrown from committing the transaction, and it is less than 120
seconds since calling with_transaction, then:
-
If the error has a
TransientTransactionError label, the transaction will be restarted.
-
If the error has an
UnknownTransactionCommitResult label, and is not a MaxTimeMSExpired error, then the commit will be retried.
If the $callback aborts or commits the transaction, no other actions are
taken and the return value of the $callback is returned.
The callback is called with the first (and only) argument being the session,
after starting the transaction:
$session->with_transaction( sub {
# this is the same session as used for with_transaction
my $cb_session = shift;
...
}, $options);
To pass arbitrary arguments to the $callback, wrap your callback in a coderef:
$session->with_transaction(sub { $callback->($session, $foo, ...) }, $options);
Warning: you must either use the provided session within the callback, or
otherwise pass the session in use to the callback. You must pass the
$session as an option to all database operations that need to be included
in the transaction.
Warning: The $callback can be called multiple times, so it is recommended
to make it idempotent.
A hash reference of options may be provided. these are the same as for
start_transaction.
This software is Copyright (c) 2020 by MongoDB, Inc.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
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