MongoDB::ChangeStream - A stream providing update information for collections.
version v2.2.2
$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) {
...
}
}
This class models change stream results as returned by the
watch in the MongoDB::Collection manpage method.
$change_stream = $collection->watch(...);
$change = $change_stream->next;
Waits for the next change in the collection and returns it.
Note: This method will wait for the amount of milliseconds passed
as maxAwaitTimeMS to watch in the MongoDB::Collection manpage or the server's
default wait-time. It will not wait indefinitely.
Users can inspect the _id on each ChangeDocument to use as a
resume token. But since MongoDB 4.2, aggregate and getMore responses
also include a postBatchResumeToken. Drivers use one or the other
when automatically resuming.
This method retrieves the same resume token that would be used to
automatically resume. Users intending to store the resume token
should use this method to get the most up to date resume token.
For instance:
if ($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.
The Change Streams manual section.
The Change Streams specification.
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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