A point in time must be opened explicitly before being used in search requests.
The keep_alive parameter tells Elasticsearch how long it should persist.
A point in time is automatically closed when the keep_alive period has elapsed.
However, keeping points in time has a cost; close them as soon as they are no longer required for search requests.
Each search request against a PIT returns in its response a pit_id field which may be different from the identifier you originally supplied.
Always use the most recently-received PIT identifier for the next request.
If you make concurrent search requests against the same PIT, Elasticsearch can return several different pit_id values in its responses.
In that case, use any of these values for later requests, preferring more recently-received values whenever possible.