/ 
MongoDB-v2.2.2
River stage two • 48 direct dependents • 56 total dependents
/ MongoDB::ChangeStream

NAME

MongoDB::ChangeStream - A stream providing update information for collections.

VERSION

version v2.2.2

SYNOPSIS

$stream = $collection->watch( $pipeline, $options );
while(1) {

    # This inner loop will only iterate until there are no more
    # changes available.
    while (my $change = $stream->next) {
        ...
    }
}

DESCRIPTION

This class models change stream results as returned by the "watch" in MongoDB::Collection method.

STREAM METHODS

next

$change_stream = $collection->watch(...);
$change = $change_stream->next;

Waits for the next change in the collection and returns it.

Note: This method will wait for the amount of milliseconds passed as maxAwaitTimeMS to "watch" in MongoDB::Collection or the server's default wait-time. It will not wait indefinitely.

get_resume_token

Users can inspect the _id on each ChangeDocument to use as a resume token. But since MongoDB 4.2, aggregate and getMore responses also include a postBatchResumeToken. Drivers use one or the other when automatically resuming.

This method retrieves the same resume token that would be used to automatically resume. Users intending to store the resume token should use this method to get the most up to date resume token.

For instance:

if ($local_change) {
    process_change($local_change);
}

eval {
    my $change_stream = $coll->watch([], { resumeAfter => $local_resume_token });
    while ( my $change = $change_stream->next) {
        $local_resume_token = $change_stream->get_resume_token;
        $local_change = $change;
        process_change($local_change);
    }
};
if (my $err = $@) {
    $log->error($err);
}

In this case the current change is always persisted locally, including the resume token, such that on restart the application can still process the change while ensuring that the change stream continues from the right logical time in the oplog. It is the application's responsibility to ensure that process_change is idempotent, this design merely makes a reasonable effort to process each change at least once.

SEE ALSO

The Change Streams manual section.

The Change Streams specification.

AUTHORS

  • David Golden <david@mongodb.com>

  • Rassi <rassi@mongodb.com>

  • Mike Friedman <friedo@friedo.com>

  • Kristina Chodorow <k.chodorow@gmail.com>

  • Florian Ragwitz <rafl@debian.org>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2020 by MongoDB, Inc.

This is free software, licensed under:

The Apache License, Version 2.0, January 2004