doc: add data_retention_num_snapshots_to_keep (#1972)

Author: BohuTANG

docs/en/sql-reference/00-sql-reference/30-table-engines/00-fuse.md

@@ -4,7 +4,7 @@ title: Fuse Engine
 
 import FunctionDescription from '@site/src/components/FunctionDescription';
 
-<FunctionDescription description="Introduced or updated: v1.2.617"/>
+<FunctionDescription description="Introduced or updated: v1.2.733"/>
 
 Databend utilizes the Fuse Engine as its default engine, offering a data management system with a user-friendly interface reminiscent of Git. Users have the ability to effortlessly query data at any given moment and effortlessly restore data to any desired point in time.
 
@@ -41,3 +41,4 @@ The following are the available Fuse Engine options:
 | row_per_block                  | `row_per_block = <n>`                               | Specifies the maximum number of rows in a file. Defaults to 1,000,000.                                                                                                                                                                                                                                                                                                                  |
 | change_tracking                | `change_tracking = True / False`                    | Setting this option to `True` in the Fuse Engine allows for tracking changes for a table.<br/>Creating a stream for a table will automatically set `change_tracking` to `True` and introduce additional hidden columns to the table as change tracking metadata. For more information, see [How Stream Works](/guides/load-data/continuous-data-pipelines/stream#how-stream-works).     |
 | data_retention_period_in_hours | `data_retention_period_in_hours = <n>`              | Specifies the number of hours to retain table data. The minimum value is 1 hour. The maximum value is defined by the `data_retention_time_in_days_max` setting in the [databend-query.toml](https://github.com/databendlabs/databend/blob/main/scripts/distribution/configs/databend-query.toml) configuration file , or defaults to 2,160 hours (90 days x 24 hours) if not specified. |
+| data_retention_num_snapshots_to_keep | `data_retention_num_snapshots_to_keep = <n>`  | Specifies the number of snapshots to retain for a table. This option works in conjunction with the `enable_auto_vacuum` setting to provide granular control over snapshot retention policies on a per-table basis. When set, only the specified number of most recent snapshots will be kept after vacuum operations. |

docs/en/sql-reference/10-sql-commands/00-ddl/01-table/90-alter-table-option.md

@@ -4,7 +4,7 @@ sidebar_position: 5
 ---
 import FunctionDescription from '@site/src/components/FunctionDescription';
 
-<FunctionDescription description="Introduced or updated: v1.2.643"/>
+<FunctionDescription description="Introduced or updated: v1.2.733"/>
 
 Sets or unsets [Fuse Engine options](../../../00-sql-reference/30-table-engines/00-fuse.md#fuse-engine-options) for a table. 
 
@@ -23,12 +23,15 @@ Please note that only the following Fuse Engine options can be unset:
 - `block_per_segment`
 - `block_size_threshold`
 - `data_retention_period_in_hours`
+- `data_retention_num_snapshots_to_keep`
 - `row_avg_depth_threshold`
 - `row_per_block`
 - `row_per_page`
 
 ## Examples
 
+### Setting Fuse Engine Options
+
 The following demonstrates how to set Fuse Engine options and verify changes with [SHOW CREATE TABLE](show-create-table.md):
 
 ```sql
@@ -59,6 +62,26 @@ Create Table: CREATE TABLE fuse_table (
 ) ENGINE=FUSE BLOCK_PER_SEGMENT='500' COMPRESSION='lz4' DATA_RETENTION_PERIOD_IN_HOURS='240' STORAGE_FORMAT='native'
 ```
 
+The following demonstrates how to use the `data_retention_num_snapshots_to_keep` option with `enable_auto_vacuum`:
+
+```sql
+-- Create a new table
+CREATE OR REPLACE TABLE t(c INT);
+
+-- Set the table to retain only the most recent snapshot
+ALTER TABLE t SET OPTIONS(data_retention_num_snapshots_to_keep = 1);
+
+-- Enable automatic vacuum to trigger snapshot cleanup
+SET enable_auto_vacuum = 1;
+
+-- After each of these operations, only one snapshot will be kept
+INSERT INTO t VALUES(1);
+INSERT INTO t VALUES(2);
+INSERT INTO t VALUES(3);
+```
+
+### Unsetting Fuse Engine Options
+
 The following demonstrates how to unset Fuse Engine options, reverting them to their default values:
 
 ```sql
@@ -70,5 +93,4 @@ SHOW CREATE TABLE fuse_table;
        Table: fuse_table
 Create Table: CREATE TABLE fuse_table (
   a INT NULL
-) ENGINE=FUSE COMPRESSION='lz4' STORAGE_FORMAT='native'
-```
+) ENGINE=FUSE COMPRESSION='lz4' STORAGE_FORMAT='native'