DOCAPI-4197: Join settings.

docs/en/operations/settings/query_complexity.md

@@ -194,4 +194,55 @@ Maximum number of bytes (uncompressed data) that can be passed to a remote serve
 
 What to do when the amount of data exceeds one of the limits: 'throw' or 'break'. By default, throw.
 
+## max_rows_in_join {#settings-max_rows_in_join}
+
+Limits number of rows in the hash table that is used when joining tables.
+
+This settings applies to [SELECT ... JOIN](../../query_language/select.md#select-join) operations and [Join engine](../table_engines/join.md) functioning.
+
+ClickHouse can proceed with different actions when the limit is reached. Use the [join_overflow_mode](#settings-join_overflow_mode) settings to choose the action.
+
+Possible values:
+
+- Positive integers.
+- 0. Memory control is disabled.
+
+Default value: 0.
+
+## max_bytes_in_join {#settings-max_bytes_in_join}
+
+Limits number of bytes in the hash table that is used when joining tables.
+
+This settings applies to [SELECT ... JOIN](../../query_language/select.md#select-join) operations and the [Join table engine](../table_engines/join.md) functioning.
+
+ClickHouse can proceed with different actions when the limit is reached. Use the [join_overflow_mode](#settings-join_overflow_mode) settings to choose the action.
+
+Possible values:
+
+- Positive integers.
+- 0. Memory control is disabled.
+
+Default value: 0.
+
+## join_overflow_mode {#settings-join_overflow_mode}
+
+Defines an action that ClickHouse performs, when the corresponding limit is reached.
+
+Controlled limits:
+
+- [max_bytes_in_join](#settings-max_bytes_in_join)
+- [max_rows_in_join](#settings-max_rows_in_join)
+
+Possible values:
+
+- `THROW` — ClickHouse throws an exception and breaks operation.
+- `BREAK` — ClickHouse breaks operation and doesn't throw an exception.
+
+Default value: `THROW`.
+
+**See Also**
+
+- [SELECT ... JOIN](../../query_language/select.md#select-join)
+- [Join engine](../table_engines/join.md)
+
 [Original article](https://clickhouse.yandex/docs/en/operations/settings/query_complexity/) <!--hide-->

docs/en/query_language/select.md

@@ -428,7 +428,6 @@ Joins the data in the normal [SQL JOIN](https://en.wikipedia.org/wiki/Join_(SQL)
 !!! info "Note"
     Not related to [ARRAY JOIN](#select-array-join-clause).
 
-
 ``` sql
 SELECT <expr_list>
 FROM <left_subquery>
@@ -465,8 +464,6 @@ Be careful when using `GLOBAL`. For more information, see the section [Distribut
 
 **Usage Recommendations**
 
-All columns that are not needed for the `JOIN` are deleted from the subquery.
-
 When running a `JOIN`, there is no optimization of the order of execution in relation to other stages of the query. The join (a search in the right table) is run before filtering in `WHERE` and before aggregation. In order to explicitly set the processing order, we recommend running a `JOIN` subquery with a subquery.
 
 Example:
@@ -524,6 +521,15 @@ Among the various types of `JOIN`, the most efficient is `ANY LEFT JOIN`, then `
 
 If you need a `JOIN` for joining with dimension tables (these are relatively small tables that contain dimension properties, such as names for advertising campaigns), a `JOIN` might not be very convenient due to the bulky syntax and the fact that the right table is re-accessed for every query. For such cases, there is an "external dictionaries" feature that you should use instead of `JOIN`. For more information, see the section [External dictionaries](dicts/external_dicts.md).
 
+**Memory limitations**
+
+ClickHouse uses the [hash join](https://en.wikipedia.org/wiki/Hash_join) algorithm. ClickHouse takes the `<right_subquery>` and create a hash table for it in RAM. If you need to restrict join operation memory consumption use the following settings:
+
+- [max_rows_in_join](../operations/settings/query_complexity.md#settings-max_rows_in_join) — Limits number of rows in the hash table.
+- [max_bytes_in_join](../operations/settings/query_complexity.md#settings-max_bytes_in_join) — Limits size of the hash table.
+
+When one of these limits is reached, ClickHouse acts as the [join_overflow_mode](../operations/settings/query_complexity.md#settings-join_overflow_mode) setting instructs.
+
 #### Processing of Empty or NULL Cells
 
 While joining tables, the empty cells may appear. The setting [join_use_nulls](../operations/settings/settings.md#settings-join_use_nulls) define how ClickHouse fills these cells.