add text

docs/en/operations/settings/settings.md

@@ -2592,4 +2592,58 @@ Possible values:
 
 Default value: `16`.
 
+## optimize_on_insert {#optimize-on-insert}
+
+Enables or disables data transformation before the insertion, as if merge was done on this block (according to table engine).
+
+Possible values:
+
+-   0 — Disabled.
+-   1 — Enabled.
+
+Default value: 1.
+
+**Example**
+
+The difference between enabled and disabled:
+
+Query:
+
+```sql
+SET optimize_on_insert = 1;
+
+CREATE TABLE test1 (`FirstTable` UInt32) ENGINE = ReplacingMergeTree ORDER BY FirstTable;
+
+INSERT INTO test1 SELECT number % 2 FROM numbers(5);
+
+SELECT * FROM test1;
+
+SET optimize_on_insert = 0;
+
+CREATE TABLE test2 (`SecondTable` UInt32) ENGINE = ReplacingMergeTree ORDER BY SecondTable;
+
+INSERT INTO test2 SELECT number % 2 FROM numbers(5);
+
+SELECT * FROM test2;
+```
+
+Result:
+
+``` text
+┌─FirstTable─┐
+│          0 │
+│          1 │
+└────────────┘
+
+┌─SecondTable─┐
+│           0 │
+│           0 │
+│           0 │
+│           1 │
+│           1 │
+└─────────────┘
+```
+
+Note that this setting influences [Materialized view](../../sql-reference/statements/create/view.md#materialized) and [MaterializeMySQL](../../engines/database-engines/materialize-mysql.md) behaviour.
+
 [Original article](https://clickhouse.tech/docs/en/operations/settings/settings/) <!-- hide -->