Provided by: libsearch-elasticsearch-client-1-0-perl_5.02-1_all bug


       Search::Elasticsearch::Client::1_0::Scroll - A helper module for scrolled searches


       version 5.02


           use Search::Elasticsearch;

           my $es     = Search::Elasticsearch->new;

           my $scroll = $es->scroll_helper(
               index       => 'my_index',
               search_type => 'scan',
               size        => 500

           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.

       This module is a helper utility that wraps the functionality of the search() and scroll()
       methods to make them easier to use.

       IMPORTANT: Deep scrolling can be expensive.  See "DEEP SCROLLING" for more.

       This class does Search::Elasticsearch::Client::1_0::Role::Scroll and


       There are two primary use cases:

   Pulling enough results
       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":

           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;


   Extracting all documents
       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

           my $scroll = $es->scroll_helper(
               index       => 'my_index',
               search_type => 'scan',          # important!
               size        => 500,
               body        => {
                   query => {
                       match => {
                           client_id => 123

           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 marry a scrolled search with bulk
       indexing is to use the "reindex()" in Search::Elasticsearch::Client::1_0::Bulk method.


       Deep scrolling (and deep pagination) are very expensive in a distributed environment, and
       the reason they are expensive is that results need to be sorted in a global order.

       For example, if we have an index with 5 shards, and we request the first 10 results, each
       shard has to return its top 10, and then the requesting node (the node that is handling
       the search request) has to resort these 50 results to return a global top 10. Now, if we
       request page 1,000 (ie results 10,001 .. 10,010), then each shard has to return 10,010
       results, and the requesting node has to sort through 50,050 results just to return 10 of

       You can see how this can get very heavy very quickly. This is the reason that web search
       engines never return more than 1,000 results.

   Disable sorting for efficient scrolling
       The problem with deep scrolling is the sorting phase.  If we disable sorting, then we can
       happily scroll through millions of documents efficiently.  The way to do this is to set
       "search_type" to "scan":

           my $scroll = $es->scroll_helper(
               search_type => 'scan',
               size        => 500,

       Scanning disables sorting and will just return "size" results from each shard until there
       are no more results to return. Note: this means that, when querying an index with 5
       shards, the scrolled search will pull "size * 5" results at a time. If you have large
       documents or are memory constrained, you will need to take this into account.


           use Search::Elasticsearch;

           my $es = Search::Elasticsearch->new(...);
           my $scroll = $es->scroll_helper(
               scroll         => '1m',            # optional
               scroll_in_qs   => 0|1,             # optional

       The "scroll_helper()" in Search::Elasticsearch::Client::1_0::Direct method loads
       Search::Elasticsearch::Client::1_0::Scroll class and calls "new()", passing in any

       You can specify a "scroll" duration (which defaults to "1m") and "scroll_in_qs" (which
       defaults to "false"). Any other parameters are passed directly to "search()" in

       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.  To send it in
       the query string instead, set "scroll_in_qs" to a true value, but be aware: when querying
       very many indices, the scroll ID can become too long for intervening proxies.

       The "scroll" request uses "GET" by default.  To use "POST" instead, set send_get_body_as
       to "POST".

           $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.

           @docs = $scroll->drain_buffer;

       The "drain_buffer()" method returns all of the documents currently in the buffer, without
       fetching any more from the cluster.

           $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.

           $total = $scroll->buffer_size;

       The "buffer_size()" method returns the total number of docs currently in the buffer.


       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 v0.90.5, but the
       call to "clear_scroll" is wrapped in an "eval" so the "finish()" method can be safely
       called with any version of Elasticsearch.

       When the $scroll instance goes out of scope, "finish()" is called automatically if

           $bool = $scroll->is_finished;

       A flag which returns "true" if all results have been processed or "finish()" has been


       The information from the original search is returned via the following accessors:

       The total number of documents that matched your query.

       The maximum score of any documents in your query.

       Any aggregations that were specified, or "undef"

       Any facets that were specified, or "undef"

       Any suggestions that were specified, or "undef"

       How long the original search took, in milliseconds

       How long the original search plus all subsequent batches took, in milliseconds.


       ·   "reindex()" in Search::Elasticsearch::Client::1_0::Bulk

       ·   "search()" in Search::Elasticsearch::Client::1_0::Direct

       ·   "scroll()" in Search::Elasticsearch::Client::1_0::Direct


       Clinton Gormley <>


       This software is Copyright (c) 2017 by Elasticsearch BV.

       This is free software, licensed under:

         The Apache License, Version 2.0, January 2004

perl v5.28.1                                2018-1Search::Elasticsearch::Client::1_0::Scroll(3pm)