Search::Elasticsearch::Client::7_0::Scroll - A helper module for scrolled searches
version 7.717
use Search::Elasticsearch; my $es = Search::Elasticsearch->new; my $scroll = $es->scroll_helper( index => 'my_index', body => { query => {...}, size => 1000, sort => '_doc' } ); say "Total hits: ". $scroll->total; while (my $doc = $scroll->next) { # do something }
A scrolled search is a search that allows you to keep pulling results until there are no more matching results, much like a cursor in an SQL database.
Unlike paginating through results (with the from parameter in search()), scrolled searches take a snapshot of the current state of the index. Even if you keep adding new documents to the index or updating existing documents, a scrolled search will only see the index as it was when the search began.
from
This module is a helper utility that wraps the functionality of the search() and scroll() methods to make them easier to use.
This class does Search::Elasticsearch::Client::7_0::Role::Scroll and Search::Elasticsearch::Role::Is_Sync.
There are two primary use cases:
Perhaps you want to group your results by some field, and you don't know exactly how many results you will need in order to return 10 grouped results. With a scrolled search you can keep pulling more results until you have enough. For instance, you can search emails in a mailing list, and return results grouped by thread_id:
thread_id
my (%groups,@results); my $scroll = $es->scroll_helper( index => 'my_emails', type => 'email', body => { query => {... some query ... }} ); my $doc; while (@results < 10 and $doc = $scroll->next) { my $thread = $doc->{_source}{thread_id}; unless ($groups{$thread}) { $groups{$thread} = []; push @results, $groups{$thread}; } push @{$groups{$thread}},$doc; }
Often you will want to extract all (or a subset of) documents in an index. If you want to change your type mappings, you will need to reindex all of your data. Or perhaps you want to move a subset of the data in one index into a new dedicated index. In these cases, you don't care about sort order, you just want to retrieve all documents which match a query, and do something with them. For instance, to retrieve all the docs for a particular client_id:
client_id
my $scroll = $es->scroll_helper( index => 'my_index', size => 1000, body => { query => { match => { client_id => 123 } }, sort => '_doc' } ); while (my $doc = $scroll->next) { # do something }
Very often the something that you will want to do with these results involves bulk-indexing them into a new index. The easiest way to do this is to use the built-in "reindex()" in Search::Elasticsearch::Client::7_0::Direct functionality provided by Elasticsearch.
new()
use Search::Elasticsearch; my $es = Search::Elasticsearch->new(...); my $scroll = $es->scroll_helper( scroll => '1m', # optional %search_params );
The "scroll_helper()" in Search::Elasticsearch::Client::7_0::Direct method loads Search::Elasticsearch::Client::7_0::Scroll class and calls "new()", passing in any arguments.
You can specify a scroll duration (which defaults to "1m"). Any other parameters are passed directly to "search()" in Search::Elasticsearch::Client::7_0::Direct.
scroll
"1m"
The scroll duration tells Elasticearch how long it should keep the scroll alive. Note: this duration doesn't need to be long enough to process all results, just long enough to process a single batch of results. The expiry gets renewed for another scroll period every time new a new batch of results is retrieved from the cluster.
By default, the scroll_id is passed as the body to the scroll request.
scroll_id
body
The scroll request uses GET by default. To use POST instead, set send_get_body_as to POST.
GET
POST
next()
$doc = $scroll->next; @docs = $scroll->next($num);
The next() method returns the next result, or the next $num results (pulling more results if required). If all results have been exhausted, it returns an empty list.
$num
drain_buffer()
@docs = $scroll->drain_buffer;
The drain_buffer() method returns all of the documents currently in the buffer, without fetching any more from the cluster.
refill_buffer()
$total = $scroll->refill_buffer;
The refill_buffer() method fetches the next batch of results from the cluster, stores them in the buffer, and returns the total number of docs currently in the buffer.
buffer_size()
$total = $scroll->buffer_size;
The buffer_size() method returns the total number of docs currently in the buffer.
finish()
$scroll->finish;
The finish() method clears out the buffer, sets "is_finished()" to true and tries to clear the scroll_id on Elasticsearch. This API is only supported since v0.90.6, but the call to clear_scroll is wrapped in an eval so the finish() method can be safely called with any version of Elasticsearch.
true
clear_scroll
eval
When the $scroll instance goes out of scope, "finish()" is called automatically if required.
$scroll
is_finished()
$bool = $scroll->is_finished;
A flag which returns true if all results have been processed or "finish()" has been called.
The information from the original search is returned via the following accessors:
total
The total number of documents that matched your query.
max_score
The maximum score of any documents in your query.
aggregations
Any aggregations that were specified, or undef
undef
facets
Any facets that were specified, or undef
suggest
Any suggestions that were specified, or undef
took
How long the original search took, in milliseconds
took_total
How long the original search plus all subsequent batches took, in milliseconds.
"search()" in Search::Elasticsearch::Client::7_0::Direct
"scroll()" in Search::Elasticsearch::Client::7_0::Direct
"reindex()" in Search::Elasticsearch::Client::7_0::Direct
Enrico Zimuel <enrico.zimuel@elastic.co>
This software is Copyright (c) 2022 by Elasticsearch BV.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
To install Search::Elasticsearch::Client::7_0, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Search::Elasticsearch::Client::7_0
CPAN shell
perl -MCPAN -e shell install Search::Elasticsearch::Client::7_0
For more information on module installation, please visit the detailed CPAN module installation guide.