anchor.diff:  automatic slicing, use these guidelines.
   
   Query performance is most efficient when the number of `slices` is equal to the
  -number of shards in the index. If that number is large, (for example,
  -500) choose a lower number as too many `slices` will hurt performance. Setting
  +number of shards in the index. If that number is large (for example,
  +500), choose a lower number as too many `slices` will hurt performance. Setting
   `slices` higher than the number of shards generally does not improve efficiency
   and adds overhead.
   
  
positive.code: == Delete By Query API
  
  The simplest usage of `_delete_by_query` just performs a deletion on every
  document that match a query. Here is the API:
  
  [source,js]
  --------------------------------------------------
  
negative.code: shards to become available. Both work exactly how they work in the
  <<docs-bulk,Bulk API>>. As `_delete_by_query` uses scroll search, you can also specify
  the `scroll` parameter to control how long it keeps the "search context" alive,
  e.g. `?scroll=10m`. By default it's 5 minutes.
  
  `requests_per_second` can be set to any positive decimal number (`1.4`, `6`,
  `1000`, etc.) and throttles the rate at which delete by query issues batches of
  delete operations by padding each batch with a wait time. The throttling can be
  disabled by setting `requests_per_second` to `-1`.
  
  