Scan/Scroll
editScan/Scroll
editThe Scan/Scroll functionality of Elasticsearch is similar to search, but different in many ways. It works by executing a search query with a search_type of scan. This initiates a "scan window" which will remain open for the duration of the scan. This allows proper, consistent pagination.
Once a scan window is open, you may start _scrolling) over that window. This returns results matching your query…but returns them in random order. This random ordering is important to performance. Deep pagination is expensive when you need to maintain a sorted, consistent order across shards. By removing this obligation, Scan/Scroll can efficiently export all the data from your index.
This is an example which can be used as a template for more advanced operations:
$client = new Elasticsearch\Client();
$params = array(
"search_type" => "scan", // use search_type=scan
"scroll" => "30s", // how long between scroll requests. should be small!
"size" => 50, // how many results *per shard* you want back
"index" => "my_index",
"body" => array(
"query" => array(
"match_all" => array()
)
)
);
$docs = $client->search($params); // Execute the search
$scroll_id = $docs['_scroll_id']; // The response will contain no results, just a _scroll_id
// Now we loop until the scroll "cursors" are exhausted
while (\true) {
// Execute a Scroll request
$response = $client->scroll(
array(
"scroll_id" => $scroll_id, //...using our previously obtained _scroll_id
"scroll" => "30s" // and the same timeout window
)
);
// Check to see if we got any search hits from the scroll
if (count($response['hits']['hits']) > 0) {
// If yes, Do Work Here
// Get new scroll_id
// Must always refresh your _scroll_id! It can change sometimes
$scroll_id = $response['_scroll_id'];
} else {
// No results, scroll cursor is empty. You've exported all the data
break;
}
}